From: W2RS, Ray Soifer Subject: More on QRP EME
Hi all,
A few additional thoughts stimulated by Tom Clark's latest note:
1. Tom's comment about synchronizing the time element so that the receiving
station would know when the data bits are
supposed to start and stop, without trying to extract that from the received
signal itself, sounds very promising. I'll take his
expert opinion about the 10-20 dB, though, because I don't have enough
information here to try to derive that conclusion
myself. If there really is that much advantage, let's all try to go for it!
One question: would GPS be the most cost-effective
way of doing this, or would a VLF time standard be easier to use?
2. On the other hand, claiming approx. 3 dB gain because the multiple tones
would be transmitted at a 100% duty cycle
instead of Morse with its approx. 50% duty cycle strikes me as double-counting.
Assuming that we're all running our
transmitters at full power, we'd have to de-rate them by the same 50% duty-cycle
factor. A transmitter capable of 100 W
on Morse would only be capable of 50 W with continuous tones. Of course, those
people using the full legal limit
(1.5 kW in the USA) would benefit from the full 3 dB to the extent that their
transmitters are capable of it, but is that
really QRP?
3. Most of the discussion I have seen on Moon-Net concerns 432 MHz and above.
I've had lots of experience with
QRP EME at 144 MHz, where libration peaks frequently last as long as 3 to 5 sec
each, long enough to get quite a
lot of information through on Morse at speeds of 15-20 WPM (12-16 baud). Going
to data rates as low as 1 baud
would give up most of the value of these signal-strength enhancements, which are
typically as strong as 4-7 dB and
sometimes as much as 10 dB. In addition, as Tom has mentioned to me in private
correspondence, received
signals during libration peaks are often far more coherent than at other times,
permitting narrower bandwith
windows to be used at such times. Since the duration of libration fading is
inversely proportional to frequency,
the use of similar techniques at 432 MHz would presumably require data rates
three times as fast as at 144 MHz.
4. At both frequencies, but especially at 144 MHz, the use of ground-reflection
gain is so valuable for QRP EME
as to be virtually mandatory, at least with conventional (i.e., Morse)
transmissions. Digital signal processing would
seem to offer the possibility of filtering techniques to reduce the noise picked
up by horizon-pointing antennas,
thus enabling ground-reflection gain to be used more effectively. I'm not aware
that anyone has yet developed
such techniques, but I'd be interested in any thoughts along these lines.
5. Brian, K6STI, makes some excellent points. I, too, love to dig weak signals
out
of the noise (as well as to provide weak signals for others to dig out, hi).
But EME'ers
as a group have always been eager to embrace any technology that will help us
make QSOs, so I suspect that both approaches (assisted and unassisted) will
always be used. Where I, personally, draw the line between "real" and "unreal"
QSOs is exactly where Ed Tilton did so many years ago: if it's in real time,
it's
a real QSO -- if you have to play back the tape later to see if you have a
complete
QSO, you don't have one. So, if the computer decodes the transmission while
you're sitting there and the QSO is still in progress, it's a good one.
73, Ray,. W2RS
From: Lee, WA8YBT/6
Greetings all:
Apparently there are sentiments both for and against low-power EME. That
surprised me a little but that's OK. There is room enough for all of us in
amateur radio.
Regarding the purported 'automated' nature of low-power EME techniques: It
was not my intention that low-power EME would be any more automated than
RTTY, just slower. The use of advanced modulation techniques and
error-correction coding does not necessarily make a QSO any more
'automated' than a voice conversation via digital cellular telephone.
Tom Clark (W3IWI) brought up a good point -- that the doppler spreading on
lunar returns won't permit the use of ultra-narrowband phase-coded
waveforms. If that is the case, a combination of coherent (FFT) and
non-coherent integration would be more effective, as he suggests. (Sorry
about the slip -- I'm used to more coherent targets.)
Regarding EME traditions: There will probably always be some EMEers
preferring the brute-force approach. (Ah yes...the crackle of high
voltage...the smell of the ozone.) But after all this is 1996 and there
may be other ways to go.
73,
Lee, WA8YBT/6
blanton@ni.net
From: James R. Miller, G3RUH
Organization: None whatsoever!
Subject: Re: More on QRP EME
On Mon, 8 Apr 1996 18:32:17 EDT Ray Soifer wrote:
Where I, personally, draw the line between "real" and "unreal"
QSOs is exactly where Ed Tilton did so many years ago: if it's in real time,
it's
a real QSO -- if you have to play back the tape later to see if you have a
complete
QSO, you don't have one. So, if the computer decodes the transmission while
you're sitting there and the QSO is still in progress, it's a good one.
There's a contradiction here. Signal processing doesn't operate in real
time. It post-processes data. Sure the delay might be only a few milli-
seconds, but it's a delay nonetheless.
Now, more hairy processing takes longer; could be a second or two. How long
are you prepared to wait before you declare it "non-real time". One second?
One minute? A week-end's hacking?
From: W2RS, Ray Soifer
Subject: Still More on QRP EME
James,
True enough, all signal processing IS post-processing and thus not in real time.
As you go on to speculate, that still leaves the issue open as to what should
be,
and should not be, accepted as being a "real" QSO.
As Brian and Ian have noted, there will always be some who refuse to accept
ANY mechanical or electronic assistance. That is one reason why the European
system of MS has never been adopted in the US, as it depends upon "playing back
the tape" or its modern, computerized equivalent. We are all in amateur radio
for
fun (at least I hope so) and if anyone doesn't want to use a computer, that's
his
Hiram Percy Maxim-given right.
That being the case, we need a functional definition of "quasi-real-time" that
will still
satisfy the relative purists, such as myself, who believe that a QSO is not a
QSO
unless it is completed during one "sitting." One solution, I believe, is
suggested by
the EME QSO protocol itself, under which you do not send a signal report until
you
have copied both call signs, you do not send "roger" until you have both calls
and the signal report, and the QSO is not complete until each station has copied
"roger" from the other. I would suggest that for a QSO to be complete, this
protocol
must be completed within the time allotted for the schedule. Most EME schedules
last half an hour and those of more than an hour are quite rare. While there is
no
absolute time limit on the duration of a schedule, perhaps the definition of a
"sitting"
might be the period during which both stations have mutual lunar visibility. If
you
lose the moon before completing the QSO, you've got to start over next time. In
practice, most QSO attempts will be for far shorter periods of time, if only
because
few operators are that patient. Still, I would argue that if it takes a
weekend's hacking
to copy a signal, it shouldn't be considered a valid QSO.
73, Ray
From: Ian White, G3SEK
Subject: Re: Low-Power EME
Laura Halliday wrote:
That is true, but it's only of historical interest. The relevant
question is why people are choosing to come into EME *today*. In most
cases I think it's a natural extension of an existing interest in weak-
signal VHF/UHF DXing. EME is simply the next step, and the technology
and the DX operating interest go hand in hand.
That would be true, but only if the premise about EME being only a
"technological stunt" were true - which it ain't.
For a lot of people, it's the balance between technology and personal
operating skill that makes EME - and VHF/UHF DX in general - so
challenging and satisfying.
Sure, but the commercial objective is a box on the wall, which the end
user can install and forget. All the fun is in the development process.
In use, commercial comms equipment is not meant to be interesting or
fun; it's only meant to work and be reliable, and in that sense be as
boring as possible. Those are good and valid objectives for commercial
comms... but they don't automatically apply to amateur radio.
One of the best things about amateur radio is that each of us can follow
our own personal path. We have many choices. If you personally enjoy
developing technology that does all the operating for you, you can go
right ahead and do that. But please don't assume that is the only
worthwhile or "right" objective in amateur radio.
From: Peter Sundberg, SM2CEW
Subject: Low power EME.
Being a very active moonbouncer for 10 years I must say that I feel rather
sad when people talk about today's EME-operating as something of the past,
it's outdated to send morse code. Well, let me tell you, it is not. EME is
about the furthest you can stretch the cooperation between technology and
the human mind when it comes to "decoding" what is being sent to you by the
other operator.
No computer "gizmo" QSO will ever produce the same satisfaction as
completing a QSO by listening yourself, and decoding the message yourself.
It is basic amateur radio, and it still lives and attracts more people every
day.
I have nothing against QRP EME with one or a zillion tones being generated
at whatever baud, and decoded by computers, but don't tell me that this is
the future of EME. EME as it is being conducted now will indeed attract more
people in the long run I'm sure. Morse code would not be in use in 1996 if
it wasn't the superior way to communicate in weak signal amateur
communications.
So, by all means, go ahead and experiment with new ways to communicate, but
don't expect us all to convert as soon as it has been done. In this regard I
am proud to be old fashioned, even at 39 years of age! (Ham for 25 years)
Moonbounce is about people talking to people, be it via the moon!
73 de Peter Sundberg, SM2CEW.
Peter Sundberg, SM2CEW
From:
From: Kent O'Dell, K2KQM
Subject: Re: Low Power EME
The ongoing discussion of the possibilities of low power EME the last couple
of days has been very thought provoking. It has caused me consider the journey
I have taken to get to the point I am currently at. (4x16 el and 1.5 KW on 144
MHz) I began trying to hear then contact W5UN with first one then two yagi's
with horizon only capability. I finally put up 4 antennas with elevation
capability and upgraded my output power to 700 watts and then finally 1.5 KW.
Hearing my own echoes for the first time was a feeling that I have yet to beat
in 15 years of ham activity! W5UN, K5GW, KB8RQ and other super stations can
obviously hear much weaker stations than the average operator due to their
large arrays. Smaller stations can also copy these super stations due to their
great EIRP. I have invested in and plan on implementing one of the Texas
Instruments DSP boards into my station to help improve my receive capability.
But, the question that has hit me with the whole low power EME scenario is who
do you talk to? Your choices seem limited to the group of super stations
mentioned before. Or, someone with above average sophistication of DSP gear.
The low power EME station may be able to copy better than the average station
with the same antenna gain but this station is limited in EIRP. Tough copy if
at all for an average EME station on the band. (I realize that we are implying
another mode of modulation than CW for these folks. This would seem to shrink
the available user community even more to those capable of the "new"
modulation method.) The last question I would like to pose is I can't quite
picture in my minds eye what an echo test would be like from one of the low
power EME stations would be like. How would an operator be able to discern
what conditions are or are not. The low power idea seems remarkably like
trasitioning from a standard "stick and rudder" approach to flying an airplane
to "fly by wire". The operator is removed one or more steps from the "process"
and is not as tightly coupled to the actual operation to maintain the "feel"
one would expect. Low power EME seems easier to persue with hardware on the
microwave bands and overcoming path loss and all the other obstacles with
antenna gain in a small package. The idea is interesting but is this the most
efficient way for a newcomer to EME with limited space for antennas to get
involved with this facet of the hobby?
Kent O'Dell/KA2KQM
From: Ray Soifer, W2RS
Subject: More re low-power EME
Peter knows whereof he speaks about pulling weak signals out of
the noise. He still holds the record for being the smallest European
station (6x16el) to work me off the moon (I was running 150 W to
1x CC3219).
73, Ray
W2RS
From: Laura Holliday, VE7LDH
Subject: Re[2]: Low-Power EME
Ian,
Thank you for your comments. A couple of points, though...
You're right, of course - except that one of the concerns that has
come up on this list, and in other forums, is that new people *aren't*
coming into EME. If people are put off by the antenna farms, huge
amplifiers, etc., adding technology to make EME more accessible may be
the way to do it.
Sure, but the commercial objective is a box on the wall, which the
end user can install and forget. All the fun is in the development
process. In use, commercial comms equipment is not meant to be
interesting or fun; it's only meant to work and be reliable, and in
that sense be as boring as possible. Those are good and valid
objectives for commercial comms...but they don't automatically apply
to amateur radio.
Of course! My point was that people have taken an specialised, weak
signal mode - meteor scatter - and, by adding technology, have built
commercially useful data networks on top of those pings. Could we do
similar things with EME? I don't care if it's commercial - I just want
to play with technology, and perhaps communicate.
I find this ironic: I have always been a very loud proponent of ham
radio being a hobby that is uniquely extensible, lacking bounds, and
able to accomodate all interests, to any extent people wish to explore
them. I am not denigrating people who want to listen for signals
buried in the noise - they impress me! My challenge is to apply new
technology to solve the problem in a different way, and possibly
contribute to a new type of communication.
Others are making it very clear that theirs *is* the right objective
(e.g. "...No computer 'gizmo' QSO will ever produce the same
satisfaction as completing a QSO by listening yourself, and decoding
the message yourself..."). I find such comments unfortunate.
From: Dave Collins, K2LME
Subject: Re: Re[2]: Low-Power EME
Hi All,
I've been enjoying the discourse, and it's reached the point I can't keep my
mouth shut any longer.
I beg to differ - don't know where you saw that new people aren't joining
the EME ranks. My experience is limited to 144 MHz, but, in my 3 years
experience, I'd estimate the QRV vs QRT ratio as at least 5 to 1. Several
have changed bands, others have added bands.
The US Navy, I believe, tried such an experiment in the late 40's using EME
for data transmission from Maryland to Hawaii. Guess it didn't work well
enough. They only had a 27 meter dish, tho.
Amateur radio packet is painful enough at its current data rate. The network
is pretty much in place - it's just on the wrong frequencies for the baud
rates sometimes desired.
A 40 MHz troposcatter data system spanned most of Canada in the 50's. It
worked, but I think they used rhombics. Talk about real estate & big antennas!
Right On, Laura. The possibilities within this hobby are what have captured
me for 40 years.
New technology is always of interest. So is the use of new technology to
improve the old and necessary. Among EME enthusiasts are a number of people
doing just that. In the past several years, efforts of which I'm aware include;
Preamps - VE7BQH, WD5AGO and others: developing preamps with noise figure,
IMD, and stability far exceeding that available commercially.
Antennas - VE7BQH, SM2CEW and others: using the latest modeling software,
performance of older commercial yagi designs has been significantly (how
about 2+ db on receive?) improved. Totally new designs of cross-polarized
yagis that really work are proving themselves well worth the effort. And,
REAL (for the moment) computer-generated stacking dimensions improve
existing arrays without modification to the yagis.
Amplifiers - K1FO designed a 1500 watt dual 3CX800 amp for 432. Previously,
the usual 1500W amp used the rare 8938, which might have cost as much as
K1FO enttire amp.
W9QXP demonstrated hefty QRO designs, using newly available Svetlana tubes,
for 144 & 432 MHz.
Software - AF9Y's FFTDSP program allows most to "see" a signal before
hearing it. For those unaware, it's a display of your receiver's audio
passband, from 300-1500 Hz in 2 Hz steps vs time, such that the received
signal draws a vertical line on your PC's screen. (I've also found it useful
for de-RFI'ing my computers and getting my HF XCVR on freq re WWV.)
W5UN, W9IP & VK3UM have programs available that will auto-track the moon
using controllers capable of the necessary resolution. The 8 bit satellite
tracking stuff won't do for the better arrays.
VK3UM's software, as I understand it, even has the ability to develop array
patterns using its tracking functions and a celestial noise source.
Efluvia - EME'ers, for the most part, become system-performance intensive.
They learn to use available measurements to document system performance, and
to notice changes. There are measurement facilities available accessed by
the usual "terrestrial" and satellite operator. As a result, EME operators
frequently find problems a terrestrial operator might call "dead band".
An example: a popular high-performance long yagi sometimes suffers the
indignation of becoming a sponge. Its feedpoint is susceptible to rain! One
EME'er bit the bullet, put grease fittings on all his yagis, and pumped the
feedpoint full of silicone grease. It worked!
I've always wondered why people made phasing lines/power dividers out of
small coax. I guess K5GW did, too. I'm sure we'll see his 432 phasing
lines/power dividers of 7/8" coax published soon.
W8MQW took a $100 Texas Instruments DSP Demo Kit and turned it into what
VE7BQH considers his "best ever" (after many) audio filter. And we know what
the commercially available DSP filters cost. Yeah, it's not as readily
flexible but that will come.
Separate Category - W2RS, who makes all the 2 meter 2-yagi-or-larger
operators feel like one of the big boys!
And, W2RS, if you're not already, you should be running with F/G8MBI for a
REAL test! Mano a mano?
Last, BUT not least. I loved W3IWI's joining the fray, and particularly his
suggestion that there may be 20 db improvement available via digital processing.
Lessee now - my antenna has about 20 db of gain. Therefore, I should be able
to do what I've been doing with digital processing and NO antenna. I LOVE
IT! Especially after last night's 11 inches of W E T snow.
Sorry, Tom. But, I do look forward to your inputs. You always throw
something new and worthy into the mix. I sometimes even understand.
From: Douglass Allen, W2CRS
Subject: LOW POWER EME IS NOW!
In a message dated 96-04-10 18:02:53 EDT, W2RS wrote:
Nobody ever said that low-power EME is easy, but it's possible to work a lot
more than the few "super-stations." With 150 W and one CC32-19, I've so far
worked 37 initials on 144 MHz EME, including 11 four-yagi stations and 2
two-yagi stations.
I've also taped my (admittedly brief) echoes and played the tape at the 1992
CSVHFS
conference. With a somewhat larger (but still comparatively small) station,
one can do >a whole lo more. PA0JMV is up to something like 200 initials
with a KW and two Yagis,and another station whose call I forget (an OZ I
think) worked 61 with a KW and one Yagi.
I haven't done anything yet with polarity switching, for example, but SM5BSZ
has gotten some outstanding results with his system that switches planes in
increments45-degree.
>Good DX and 73,
Ray W2RS
Ray,
I was delighted to see your message stating that low power 144 EME is
occuring right now with conventional equipment and in real time! Perhaps,
some of those discussing the topic would be amazed at what 144 EME stations
are accomplishing.
Doug W2CRS Publisher-Editor of VHF EME REPORT.
From: Bjorn Aldorsson, SM7SJR
Subject: RE RE RE RE Low power EME
I agree with what SM2CEW wrote.
I can not see the fun (or the point in) making a computer "gizmo" EME-qso.
The whole idea to EME is the beautiful sound of weak-sigs cw!!! I don't use
more computer-aid than VK3UM-soft for printing out moon-position.
The idea of detecting a qso on the screen instead of in the loud-
speaker sounds like nothing more exciting than to see if my latest config
of JNOS-compilation will compile without any errors or not! Thanks but no
thanks.
I used to live in a flat before, and therefore no EME. Now I have moved to a
house with few neighbours. Why? Because I want to wrk EME and if the actual
situation for me doesn't allow me to wrk EME I do something about it!
And I suggest that you guys out there do the same, because EME the old
fashioned way is no1!!!
73 de SM7SJR / Bjorn.
4 x 17B2 and 1kW. Not much but on ocasion there is a qso in the log!
From: Bill Gioia, K2EK
Subject: Re: Low-Power EME
In a message dated 96-04-09 09:33:34 EDT, G3SEK@IFWTECH.DEMON.CO.UK (Ian
White, G3SEK) writes:
Laura Halliday wrote:
Couldn't the same be said for low power EME?
Speaking from the perspective of someone building towards EME capability
(albeit, at a snails pace), I agree fully with Ian's comment. In my case, the
attraction lies in the same *operator* related challenges which first
interested me in top-band DXing, QRP DXing and VHF/UHF weak signal work. EME
is just another venue for applying those operator skills and enjoying the
satisfaction of doing something uniquely difficult.
Granted, technology enters into building an EME station. Just as it does to
build a station capable of working 250+ countries on 160m or 100+ grids on
70cm... But for me, that is secondary to sitting down and using it to push
my operating skills to the limit.
Bill K2EK
From: Moritz Heintze, DL5UH
Subject: Re: Low power EME.
Peter,
I must whole heartedly agree with you, the challenge is the difficulty.
Surely,
But as yet we do not need to fear that CW / weak signal skills
are rendered obsolete by fully automated data transmission.
To my knowledge the capability of new digital transmission and error
correction to chop 10 to 20 dB off the power needed has
yet to be demonstrated.
73, Moritz, DL5UH
From: In space, no one can hear you snore. Dan Schultz, N8FGV
Subject: Re: Low power EME
I am a recent arm chair subscriber to Moon-net, being an apartment dweller
my EME ambitions must be on hold for a few more years at least. I have
been following the "Low Power EME" thread, after reading comments of the
following sort I am motivated to delurk and throw in my two cents:
I must whole heartedly agree with you, the challenge is the difficulty.
If it was a real easy thing to, like using this computer to make the contact,
I would never try it more then once! Each contact is unique, never the same
from one weekend to the next, isn't it great?!
I have a feeling that if I were to set my time machine to go back about
80 or 90 years, I would no doubt hear some ham arguing that "Those new-
fangled vacuum tube gizmo's will never produce the same satisfaction as
tuning a signal with a cat's whisker and galena crystal. Vacuum tube
receivers and continous wave transmitters make it too easy, a real ham
knows how to tweak his cat's whisker to find the sweet spot on his galena
crystal to pull in the weak signal from those kilowatt spark gap
transmitters. A real ham wants the challenge of doing it the hard way."
My own personal bias is in favor of homebrew radio equipment. I don't
see how any ham can enjoy making QSO's with a storebought radio, where
all you have to do is call up a toll-free 800 number and read off your
credit card number. A real ham ought to be able to launch a signal into
the air and pull out a reply with equipment of his own making. However,
I don't belittle others who don't share my thoughts, or accuse them of
not being true hams because they didn't know the satisfaction of
soldering together their own rig. There ought to be enough room in
amateur radio for all points of view about what constitutes "satisfaction".
The object of both forms of EME (low-power vs traditional) is to get a
message through under sub-optimium conditions. Some people prefer to do
it with full legal power and a well trained ear, and others derive equal
satisfaction by using the wonderful new silicon chips that have recently
become available to us to accomplish the same goal, using brains rather
than braun.
Is this ALWAYS going to be true, or might there not be some new technology
that might do even better as a weak signal mode? Go visit Phil Karn's web
site (http://www.qualcomm.com/people/pkarn/fecdemo) for a possible
challenge to King CW.
So, by all means, go ahead and experiment with new ways to communicate, but
don't expect us all to convert as soon as it has been done. In this regard I
am proud to be old fashioned, even at 39 years of age! (Ham for 25 years)
Moonbounce is about people talking to people, be it via the moon!
Or via computers and the moon.
I don't think that anyone here has argued that low power DSP moonbounce
was superior to conventional high power EME. The arguments about what
is or is not a legitimate QSO seem to be coming from the traditional
EME supporters. DSP assisted moonbounce was simply put forward as a
possible way for more hams to reflect a message off of the moon using
the modest equipment that they may already possess.
What? You use a computer to find the moon? Shouldn't you be doing it in
some more "traditional" way, perhaps with a slide rule, or by sighting
the moon visually? Wouldn't it be more satisfying to use your native
skill to find the moon rather than allowing a computer to do the work
for you?
You suggest that I quit my job in the Washington DC suburbs and move away
from Maryland to a state where land is cheap and they never heard of
homeowner's associations or covenants so that I can build a "traditional"
EME station? While I have entertained that thought in my dreams, there
are certain practical employment related reasons why I choose to remain
here in the urban jungle. Therefore low power EME with perhaps an oscar
class station will probably be the only option, at least until I reach
retirement age.
Dan Schultz N8FGV
From: Tom Clark, W3IMI
Subject: Do ya have to hear 'em to work 'em???
cc: ka9q@amsat.org
Since my posting last week, I'm glad to see that a lot of discussion has
been generated! Much of the philosophical comments have centered on the
age-old "you've got to hear 'em to work 'em" topic!
In response to that issue, let me ask a gedanken question of those who
espouse the "earball" philosophy: How about two deaf amateurs who work
each other off the moon with RTTY. Is that a "legal" QSO?
Let's now extend the idea from RTTY to a packet radio like mode to
address the "post processing" theme. In packet, a message is assembled
and transmitted as an entity. The receiving station gets the entire
frame and uses a CRC test for validity based on the contents of data
received. Only after the entire frame is received and the CRC test is
passed is the message presented to the user. A few seconds time pass
between the time the sender types in the message until the receiver
sees it. Does this pass the "real-time" test?
The packet analogy is the next step past RTTY. Nobody in his (or her,
for Laura's benefit) right mind wants to listen to the raucous sounds of
RTTY or packet, and even if you hear them, the brain will have a difficult
time decoding them. Some other entity (in the early days a mechanical
teleprinter, or in the modern era a computer) does the tedium of figuring
out what the bits actually mean.
Nobody seems "offended" by the idea that DSP-based filters (implemented in
software and silicon) are any less "pure" than filters that are
made with various combinations of L's,C's, quartz crystals, and slabs
of ceramic. I showed the results of using FFT spectrum scanners in the
'80s at "big dish" EME expeditions in WVA, Alaska, etc. Modern signal
processing is not magic and it is not exotic. It's in common use today.
What I have been suggesting is an extension of the RTTY/packet scheme
optimized for weak-signal work with some technology that can be easily
realized.
Let me describe what I view of a "QSO". First let's think about the data
that makes up a QSO. For many years I have adopted the definition that
a minimal QSO must consist of:
Let's take a look at the data content of this:
- Each call consists of 3 (for the rare JY1 case) to 6 letters plus
digits. If we use the Roman alphabet, there are 26 letters + 10
digits so there are 36 possible characters. Such a character can
be transmitted in 6 bits (64 states) or less (actually only ~5.2
bits are needed with sophisticated coding). Take the worst case
with 6-letter calls and no coding, we get 72 bits.
Ok, that totals 72+18+8 = 98 data bits to make a QSO that is more rigorous
than what is done today!
We have to do some more rigorous tests on the "gain" of this scheme. The
critical elements of the scheme involve:
Back-of-the-envelope estimates (like I showed at CSVHFS last summer) of
the use of time-synchronous data plus the use of coding plus the use of
frequency-domain filters matched to the signal characteristics give the
strong hint that there is at least 20 dB of "gain" possible. This may not
be of interest to the "big-gun" EMEers, but it opens up the possibility of
EME operations between OSCAR-class stations -- the folks who have only
had a hint of the possibility of working EME in the past [like with
VE3ONT(Algonquin 150'), W3IWI/K8HUH(Greenbank 140'), Arecibo, etc.).
Thanks for all the responses -- let's keep the dialogue going!
73 de Tom, W3IWI
From: Bill Boman, N0LIK
Organization: Party Line Entertainment Network
Subject: Low Power EME
Another way to look at low power EME is to do the best we can in all areas;
power,antennae,transmission lines,preamps,filters (analog or
digital),protocol,timing,coding,spread spectrum,multi-tone channel, etc.
Judge the best you can by time,money,neighbors,geography,and how good the
results are. Then we can follow the FCC rules and reduce our power output for
the particular QSO in progress.
If we sstart out with the requirements that our EME system not have an antenna,
nor a power output, norbe noticeable by the neighbors, it is obviously
impractical.
If Tom Clark and Phil Karn can come upt with ways to save 20db that's great and
if I can afford it I'll try to implement the savings. However, if I understand
the path losses associated with EME, that really wouln't mean a whole lot. My
3.2wl 432mhz yagi tests at 14dbd. This means I would need 32yagis stacked to
have ~29dbd gain. If I split Tom Clarks 20db savings between antennae and
power out, I would still need a stack of 16 of these yagis and a power out of
750w (half the planned 1500w). The
neighbors couldn't help but notice and I wouldn't have as capable a system. If
Tom and Phil could come up with a way to save 150+db then we'd
really have something. We might even get to the point were EME was a
consistently dependable mode of SSB communications as long as the moon was
LOS. It will be interesting to hear what they have to say at the July
CSVHFS conference. Forward error correction and packet methods may also
apply. As previoously stated, my goal is to get all I can and then ccut back
to suit the QSO.
I need to state that I have been reading Tom Clark and Phil Karn for some time
and wish to compliment them on being the authorities on these subjects for
amateurs. If I ever finish my system their efforts will be included as will
the antenna and amplifier work by Steve Poulishen.
I guess what I'm trying to get across is that there is no set of require-
ments that fits all (except the 'best') and for that reason it would be more
advantageous to discuss and research specifics rather than a no-system that
'meets' all requirements. Each of us must make his own
db & $ budget.
Phil Karn is proving that signal processing on a low cost Pentium PC is
doable withoout special digital processing black boxes.
Tom Clark is coming up with his Totally Accurate Clock (TAC) for extremely
accurate timing based on GPS. TAPRis about to work up some kind of
undefined kit to implement this.
Steve Poulishen has excellent antenna and amplifier designs.
Who are the authorities on transmission lines, power splitters, T/R
switching, and preamps???
BTW, is you are really looking for a small, low power system for EME
you might consider 10GHZ (small dish, lo-poweer TWT).
Inputs are welcome.. Bill Boman N0LIK CSVHFS wtb@partyline.org
From: Ray Soifer, W2RS
Subject: ESP vs. DSP
Hi,
Further to Tom's latest note, "Do You Hafta Hear 'em to Work
'em?":
I'm a little concerned that we've begun to throw figures
around (e.g., "20 dB gain") without adequately defining the
reference point. So, I thought I would take a stab at doing
that by using Tom's methodology to probe the limits of
present-day Morse EME communication. To me, any new
technology has value in direct proportion to the improvement
it would produce over that, e.g., if it takes a minimum of
100 units EIRP to complete a QSO with the best present
technology and a new system can do it with 50 units, then
the new system is 3 dB better than the present one.
Let me also be presumptuous enough to assume that my own
rather extensive QRP EME log can be used as an example of
the best that has been achieved with present technology. I
hasten to add, of course, that I was not the person who
achieved this, but rather it was accomplished by the 37
different people who dug my QRP signals out of the noise to
complete QSOs with me over the last 10 years. (I no longer
hold one end of the record for the smallest station to
complete a 144 MHz EME QSO; this is held by CO2KK and KB8RQ,
who worked in 1992 with Arne running 22 measured watts to
two 5-element yagis, EIRP about 450 W. However, analysis of
this QSO shows results fully consistent with the findings
presented here.) The W2RS log data from which these findings
are extracted were published in the Proceedings of the Tenth
AMSAT-UK Colloquium, held at the University of Surrey in
1995 and available in book form from AMSAT-UK.
Taking actual path degradation (due to lunar distance and
sky noise) into account but not polarity mismatch (i.e.,
assuming that Faraday matched the polarities at some time
during the QSO), complete QSOs were achieved on prearranged
skeds with received signals from W2RS as weak as 16 dB below
an arbitrary reference point when mutual ground gain was
utilized and -10 dB using ground gain only at W2RS.
However, when only random QSOs are considered, the best
result achieved was -4 dB. For this purpose, I
conservatively assumed that no mutual ground gain QSO could
be considered random as it may have been possible for the
receiving station to copy my direct signal on tropo and thus
to know that I was calling him before actually copying my
signal off the moon.
For each QSO, the arbitrary reference point (i.e., 0 dB) was
calculated using standard EME path calculation software,
taking into account the actual path degradation at the time
(i.e., lunar distance and sky noise) but not polarity
mismatch (i.e., assuming that Faraday produced an
approximate polarity match at the time signals were actually
copied). The noise bandwidth was assumed to be 100 Hz,
which is generally consistent with the signaling rate
employed, i.e., Morse at approximately 20 WPM. The
reference point calculation did not take ground gain into
account, so that if this is assumed to be approximately 4 dB
at each station (an assumption believed to be accurate
plus/minus 1 dB), then QSOs with no mutual ground gain
(i.e., ground gain only at W2RS) were achieved with signals
6 dB below what should have been theoretically possible
and with mutual ground gain, 8 dB below.
This result of 6 dB to 8 dB "gain" was achieved by the use
of experimentally derived operating techniques intended to
optimize the use of favorable propagation phenomena,
primarily libration fading and ionospheric scintillation
effects; these techniques were described more fully in my
paper presented to the 1992 CSVHFS Conference.
In the present context, the difference between scheduled and
random QSOs is extremely significant. In random working, it
was not possible to complete QSOs with signals weaker than
what could be accounted for by ground gain alone, but
scheduled QSOs were achieved with signals 6 dB to 8 dB below
this. Therefore, the receiving operator's prior knowledge
of the call signs enabled him to copy signals 6 dB to 8 dB
weaker than he would have been able to copy were the call
signs unknown to him. This knowledge thus enabled his
"cerebral signal processor" to narrow the effective noise
bandwidth of the channel to somewhere between 14 Hz and 25
Hz, even though the actual signal being received was
approximately 80 Hz to 100 Hz wide. This effect, I
believe, is analogous to what Tom hopes to achieve through
time synchronization of the transmitted signals.
Since my call sign contains only four characters (but the
other call sign can have up to six), we have ten possible
characters vs. Tom's 12. Then, since in 2m EME we transmit
only callsigns, Os and Rs, I calculate that we would have,
at most, 62 bits rather than Tom's 98 (Tom, check me on this
please). Those 62 bits must be transmitted in approximately
30 times 57 seconds each way, or approximately 1,710
seconds, for a data rate of 0.0363 baud. The difference
between that and the actual signaling rate of 20 WPM or 16
baud represents the redundancy employed in our "cerebral
error correction system."
Another way of looking at this redundancy would be that a
perfect system would be able to come within 1.6 dB of that
0.363 baud, or about 25 dB better than what we have been
able to achieve using ESP rather than DSP.
If we look at this in yet another way, AF9Y has demonstrated
experimentally that 2 Hz is about as far as one can usefully
narrow the receiving bandwidth to detect, but not to copy, a
2m EME signal. The difference between that 2 Hz and the
effective bandwidth of 14 to 25 Hz needed to copy a Morse
EME signal by ear and brain would represent about 7 to 12 dB
of potential improvement under actual EME conditions.
That's only about half the 20 dB potential improvement
claimed by some, but would still represent a very meaningful
amount.
OK you DSP jocks out there, let's see how much of that
potential improvement you can realize in practice!
73, Ray
From: Ian White, G3SEK
Subject: Re: Low-Power EME
Apologies for the delay in replying due to a weekend break (overnight
ferry to France; party; overnight ferry home) - not my normal lifestyle
but good training for EME contests!
I'm replying mainly to Laura, VE7LDH's thoughtful posting, but will be
taking in other people's points as well. She very accurately summed up
the whole reason for the debate:
That's exactly it - it's a matter of personal viewpoint and choice.
One viewpoint is mainly technology-oriented, and the communication is
secondary, maybe even optional. The other viewpoint cares first of all
about the nature of the communication, and is more selective about the
technology it wishes to use.
In other words it's a matter of personal viewpoint. That's absolutely
fine - the moon belongs to everyone.
The discussion seems to be splitting into three topics which really
should be kept separate:
1. How far do we want EME to go computer-assisted?
First let's try to define "computer assistance". The real dividing line
in this debate is about who or what does the "listening": is it the
operator or is it the computer?
The "traditional operators" insist on their own ears and brains being
fully involved, because we want the QSO to stretch and extend our
personal capabilities. That's why we would find it deeply unsatisfying
to just sit there and watch what the computer has decoded. This is
purely based on the kind of personal satisfaction we want to get from
EME, and from amateur radio in general.
Make no mistake: we're willing to use any technological assistance we
can lay hands on - but stopping short of the point where the technology
doesn't need the operator any more. For example, at least 10 CPUs,
ASICs, DSPs and other digital devices contribute to almost every EME QSO
that I make - but it's still myself who operates the station and makes
the QSOs. I'll take the credit, but must also accept any failures caused
by my own limitations, because that too is part of my choice.
Ray, W2RS, has summarized the kinds of techniques that EME operators
have been using to extend their capability to work smaller and smaller
stations. My own is a small station by most standards, but I want to be
able to work other stations that are smaller yet. I'll use any kind of
technology to do that, UNLESS it cuts me out of the system.
This is a good place to mention "QRP". I think the insistence on low
power is misleading, because the main limitation on EME for most people
is lack of antenna space. This is England, so I know what lack of space
means! In such circumstances, if you want to make difficult QSOs, you
build high-power amplifiers and tackle any EMC problems that arise,
because that is something you *can* do to improve your station without
moving house.
G3RUH asked a good question: how far away from real time are you willing
to stray? If the QSO is supposed to be in "real time", my personal limit
would be a few seconds. Beyond that, it no longer feels like real time
to either operator, so the whole nature of the contact has changed.
Once that line has been crossed, I don't have any problems about the
validity of scheduled, computer-assisted EME QSOs that take hours and
hours. The same applies to European-style meteor-scatter QSOs assisted
by speed-shifting. The important thing is that the distinction is
recognized on QSL cards and in contest listings and award programmes.
Forgive me if the context of that last sentence made it look as if it
was criticizing Laura, VE7LDH. It wasn't. The two sides of this debate
simply want to do things different ways, on the basis of personal
preferences. Because this is amateur radio, such choices are not open to
criticism in any form.
VE7LDH said:
I agree - the same applies to sneers and catacalls from both sides.
Let's all stop that, folks, and get on with a constructive debate.
From: Joe Lynch, N6CL
Subject: Re: Low Power EME
With all this talk about lower and lower power and increases in possible
gain, it appears that the wolf has had it right all along.
All it has to do is go out on a full moon night, bay at it, and back come its
echoes.
73 de Joe, N6CL
For remarks, typos, changes etc: Rein W6/PA0ZN
============================================================================
James R Miller E-mail: g3ruh@amsat.org
Cambridge England Stardate: 1996 Apr 09 [Tue] 0728 utc
============================================================================
As for myself, I don't see why electronic
assistance
should be automatically barred. RTTY QSOs are accepted for DXCC credit, and
how many of us can copy Baudot, ASCII or Pactor by ear?
EME operation started as a technological stunt (let's not kid
ourselves here...),
and if that's all people want it to be, it will
remain sterile and die out.
If it's to amount to anything, it needs to
be much more, and sophisticated modern technology is the key. Just
think of what commercial interests are doing with meteor scatter
packet!
73 from Ian G3SEK Editor, 'The VHF/UHF DX Book'
'In Practice' columnist for RadCom (RSGB)
Professionally:
IFW Technical Services Clear technical English - anywhere.
Now THAT is where the challenge is, and this is what makes so many operators
turn their antennas, big or small to the moon every weekend, to try and
stretch their abilities a bit further. They want the challenge.
P>
...The relevant question is why people are choosing to come into EME
*today*. In most cases I think it's a natural extension of an
existing interest in weak- signal VHF/UHF DXing. EME is simply the
next step, and the technology and the DX operating interest go hand
in hand.
Just think of what commercial interests are doing with meteor
scatter packet!
One of the best things about amateur radio is that each of us can
follow our own personal path. We have many choices. If you
personally enjoy developing technology that does all the operating
for you, you can go right ahead and do that. But please don't assume
that is the only worthwhile or "right" objective in amateur radio.
Laura Halliday VE7LDH "C'est une femme mutine, assez
lhalliday@creo.bc.ca elegante, grave et legere, ayant le
ve7ldh@amsat.org sens du confort et du plaisir
Locator: CN89mg en tout." - C. Deneuve
You're right, of course - except that one of the concerns that has
come up on this list, and in other forums, is that new people *aren't*
coming into EME. If people are put off by the antenna farms, huge
amplifiers, etc., adding technology to make EME more accessible may be
the way to do it.
Of course! My point was that people have taken an specialised, weak
signal mode - meteor scatter - and, by adding technology, have built
commercially useful data networks on top of those pings. Could we do
similar things with EME?
I find this ironic: I have always been a very loud proponent of ham
radio being a hobby that is uniquely extensible, lacking bounds, and
able to accomodate all interests, to any extent people wish to explore
them. I am not denigrating people who want to listen for signals
buried in the noise - they impress me! My challenge is to apply new
technology to solve the problem in a different way, and possibly
contribute to a new type of communication.
73, Dave K2LME Lyme CT USA k2lme@pcnet.com
w2rs@amsat.org
PA0JMV, whom you refer to above, has worked 455 grids, 91 countries, and 50
states with his two yagis! Other 2-yagi stations have also worked 50 states
and over 50 countries.
SM4BSZ, whom you refer to above, is very competitive with his innovative
four yagi station with polarity rotation and, to the best of my knowledge,
had the top score in a recent (March) EME contest competing against several
8, 16, 32, and at least one 48 yagi station.
F/G8MGI has contacted over 60 stations, including many without schedules,
with his single yagi with polarity switching. He has worked several 2-yagi
stations. Working him and a number of 2-yagi stations has been a big thrill
for me. KB6IGC with two yagis (armstrong rotation) and 325 watts, if my
memory serves me, was, for me, a very exciting contact last summer when I
worked him by schedule twice and without a schedule a third time.
I am certainly not against progress (and could do nothing about it if I
were!), but I have to admit that I find the challenge of things like EME my
main incentive for doing them. If technological advances give us the 10 dB
improvement that some of you have suggested, I don't know if there would
remain sufficient challenge for me personally to stay excited by 144 EME, at
least with my 4-yagi station. I'm also not sure I would find satisfaction in
finding out that my computer had worked another station. I want to hear and
decode the signal, at least in part, with my own ears! In fact,my greatest
thrill in EME, was hearing my own echoes the first time.
But, whatever the future holds, EME with an HT or you name it, the great
thing about this hobby is that there are an infinite number of challenges
that will always remain!
EME operation started as a technological stunt (let's not kid
ourselves here...)
.... The relevant question is why people are choosing to come into EME
*today*. In most
cases I think it's a natural extension of an existing interest in weak-
signal VHF/UHF DXing. EME is simply the next step, and the technology
and the DX operating interest go hand in hand.
No computer "gizmo" QSO will ever produce the same satisfaction as
completing a QSO by listening yourself, and decoding the message yourself.
It is basic amateur radio, and it still lives and attracts more people every
day.
Morse code would not be in use in 1996 if it wasn't the superior way to
>communicate in weak signal amateur communications.
One of the best things about amateur radio is that each of us can
follow our own personal path. We have many choices. If you
personally enjoy developing technology that does all the operating
for you, you can go right ahead and do that. But please don't assume
that is the only worthwhile or "right" objective in amateur radio.
I can not see the fun (or the point in) making a computer "gizmo" EME-qso.
The whole idea to EME is the beautiful sound of weak-sigs cw!!! I don't use
more computer-aid than VK3UM-soft for printing out moon-position.
The idea of detecting a qso on the screen instead of in the loud-
speaker sounds like nothing more exciting than to see if my latest config
of JNOS-compilation will compile without any errors or not! Thanks but no
thanks.
I used to live in a flat before, and therefore no EME. Now I have moved to a
house with few neighbours. Why? Because I want to wrk EME and if the actual
situation for me doesn't allow me to wrk EME I do something about it!
And I suggest that you guys out there do the same, because EME the old
fashioned way is no1!!!
Greenbelt, MD
n8fgv@amsat.org
- Exchange of calls of both stations
- Exchange of some unknown information both ways (usually signal
reports and/or Grid Squares and/or contest zones, etc)
- Bidirectional acknowledgement of the receipt of the calls+info
- For the unknown information, I'd propose we send signal reports
AND the 4-character 1deg by 2 deg Grid Square. An 8-level signal
report has twice the resolution of the present TMO5 and requires
3 bits. There are 180*180 = 32400 possible "FM19" like grid
squares, and this requires 15 bits (32768 states) to transmit.
So the information field takes 15+3 = 18 bits.
- I suggest 8 bits for the bidirectional "QSL" field. Each station
adds bits when it receives a crucial required piece of information
(1 bit when I copy my call from you, 1 bit for your call, 1 bit for
when I copy a non-zero signal report and one bit when I copy your
grid square), for a total of 4 bits. The other 4 bits I send are
the echo of the "QSL" bits I see from you. When I have assembled
a "1111 1111" field, I can quit transmitting, and the QSO is complete
(i.e. "1111 1111" = SK).
In my earlier note I suggested that the data would be sent at a rate of
1 Baud, i.e. one signaling element per second. Lets assume we use a 1 minute
sequence length. We can transmit 57 signal elements in that period (for
EME we have to allow for the 2.2 second round-trip travel time). Phil and I
have been suggesting a multi-tone FSK scheme, and pragmatic arguments
(like the spectral broadening of the moon echo, TX/RX frequency control
accuracy and the use of off-the-shelf radios with SSB filters) leads to
5 or 6 tone "channels" as being best.
Take the N=6 case: in the one minute sequence, I have 57*6 = 342 time/
frequency cells. Some of the 342 are not useful. We probably want to discard
the one case where no tones are on, the 6 cases where only a single tone
is on and the 15 cases where only 2 tones are on and the one case where
all 6 tones are on, and the 6 cases where 5 tones are on leaving 342-29=313
"good" sequences in which to transmit 98 bits of data. the excess ratio
313/98 = 3.19 is used for redundancy coding for error correction. Each of
the 98 data bits appears in (i.e. is spread into) the equivalent of 3.19
of the time/frequency "cells".
The entire 57 second sequence with 342 possible time/frequency cells is
received and examined in a maximum likelihood decoder to extract the 98
data bits. The decoder reconstructs the bit string and is able to flag
those bits that cannot be decoded properly based on the available data
(which may need to be filled in during the next 1-minute sequence). Phil
has been experimenting with many different decoding algorithms (Fano,
Viterbi and others) and I leave it to him to discuss the "best" to use.
The decoder should be able to "munch" the data stream in a second or so
(assuming a Pentium). Therefore -- as with my earlier "packet" analogy --
the results are available to you only slightly later than "real time".
- The use of digital data buried in the noise
- The use of frequency domain (probably FFT-based) filters to extract
every last photon from the signal
- The use of precisely timed signaling elements to avoid the need to
recover data clock (using GPS)
- The use of signal coding to optimize performance
- Use of your existing radios plus a Pentium-class computer equipped with
a "Soundblaster".
(he of the ringing ears)
w2rs@amsat.org
Could we do similar things with EME? ...
I just want to play with technology, and perhaps communicate.
2. Are computer-assisted QSOs ethical/valid?
3. What can we expect from computer assistance and how can we accomplish
it?
Earlier, I said:
One of the best things about amateur radio is that each of us can
follow our own personal path. We have many choices. If you
personally enjoy developing technology that does all the operating
for you, you can go right ahead and do that. But please don't assume
that is the only worthwhile or "right" objective in amateur radio.
Others are making it very clear that theirs *is* the right objective
(e.g. "...No computer 'gizmo' QSO will ever produce the same
satisfaction as completing a QSO by listening yourself, and decoding
the message yourself..."). I find such comments unfortunate.
73 from Ian G3SEK Editor, 'The VHF/UHF DX Book'
'In Practice' columnist for RadCom (RSGB)
Professionally:
IFW Technical Services Clear technical English - anywhere.