RE: [linrad] Tigers about to land here

[Leif Åsbrink <leif.asbrink@xxxxxxxxxxxxxxxxxx>]

Hi All,

I have got a few questions from Roger (W3SZ) that I 
think is of general interest so I send my answer here 
to the list.
 
> This is a MUD report with a few questions for Leif (the main one is:
> should I run the DC from the power supply to the RX2500 in shielded
> cable, or is the zipcord (heavy duty and color coded) I run everywhere
> else OK?  I have a very nice box to put the power supply in, and I want
> to do it right the first time ;)
The power supply cord is not critical. Use anything you have at hand
that fits to a d-sub. The RX 2500 needs three wires only but the
other units need five wires for the PC interface (to set LO frequency).

The WSE RX converters are 50 ohm building blocks. I do not know how
they will be used by others so I have only vague plans for a "control 
unit" at the present time.

A "control unit" would take care of band switching. If someone wants to
use Linrad for ALL the ham bands, there will be a need to switch in and
out several different converters. Even if I will be able to make a HF
to 70MHz converter for all HF bands in a single box it might be desireable
to switch between different antennas for different HF bands. Units for
50->70MHz and 144->70MHz will be separate boxes, one would like to
switch off those not in use since they consume about 0.5A each.
For the microwave bands converters to 144, 50 or 28 have to be switched 
in and out. One might also want to switch in preamplifiers, filters  or
attenuators.

Before the control box exists one will move the d-sub and the coaxial cables
between the HF and the 144 MHz unit by hand.

You will need four 9-pin d-sub connectors with the DC supply pins
connected to +/- 15V for all of them. Pins 2,3 and 6 should be connected 
in parallel and pin 1 for each d-sub should be routed to separate
data pins of the PC parallel port. The groups of parallelled pins 2,3 and
6 should also be routed to the PC parallel port. (details later) 
  
> 2.	Why are there 4 boxes (144>70 MHz, 70>10 MHz, 10>2.5 MHz, and
> RX2500, instead of just 1 or 2 or 3?
> 	Several people asked me this and I said I thought that it was
> for performance reasons and to maintain general utility of radio, but
> they wanted to know more than that.  They asked specifically why 70 MHz,
> and I guessed that it was because it is a common IF frequency with lots
> of parts.
The reason is that the only way to make a good oscillator I know of
is to use a crystal. With 5 X-tals in RX70 and 4 X-tals in RX10700
one gets 20 different center frequencies at 70MHz. The different
center frequencies are separated by 25kHz so the coverage is 500kHz.
There is an additional 92kHz or so for the Delta44 bandwidth.

The frequencies are selected not because any standard parts are used
but because many old receivers use 10.7MHz so one might take the wideband
output from e.g. IC202, FT221 or similar and route into the 10.7MHz input.
As a second level one might take the LO from any receiver that uses 10.7MHz
IF and use for a pair mixers to make a two channel receiver.

Many modern HF receivers use 70MHz for the first IF. One can pick the wideband
70MHz signal from any of them and route into the RX70 or one can use the 
LO from such a radio to make a two channel receiver with two standard mixers.

The frequency ratios are suitable and allow adequate suppression of mirror images.
 
> 3. Can it be used with JT44?  I said that it could, but that the
> 2nd FFT bin width would need to be set 'right', and that processing
> delay could be a problem if parameters with long processing delays were
> chosen.  I told Joe Taylor K1JT  that I thought that JT44 could be very
> interesting if fed with adaptive polarization rotation and constantly
> optimized signals such as Linrad might do.  I would think that the
> Linrad FFT2 bandwidth would need to be 2 Hz or less, since the bin width
> is about 5.4 Hz with JT44.  And since the JT44 delay may be up to 4
> seconds and eme delay is up to 2.7 seconds, we would neet to keep Linrad
> delay to less than 1.5 seconds.  As I am now running I nave a total
> delay of 3.23 as specified when I hit 'T'.  If we got into the JT44
> software, maybe we could separate out the receive and transmit times and
> provide for an adjustable offset of the receive delay.  For setting the
> FFT2 bandwidth, I guess if FFT 1 bandwidth were set at 10 Hz and FFT2
> bandwidth reduction were set at 2 powers of 2 that would give 2.5 Hz
> bandwidth for FFT2, and that is what we would want.  Is that correct?
At the moment there is no JT44 code inside Linrad. The present routines
are optimised for weak CW and it is assumed that the baseband bandwidth
fits well to the bandwidth of a CW signal.

To use Linrad for JT44 you presently need a second computer running JT44
while Linrad runs in "SSB mode". With a bandwidth of 5Hz for FFT2 and a
large number for FFT32 averaging you will see the two spectra for the two
polarisations in the high resolution graph with a sensitivity similar 
to that of JT44. Use "fixed" polarisation and set the pol parameters 
for the signal to be visible in the green spectrum only. If you allow 
enough storage time for FFT2 the new spectra will come immediately on 
screen after each change of the polarisation parameter. The time delay
will be less than 1 second because FFT2 is the only narrow filter and
you may use it with window N=1 to make the delay small if there are no
strong signals at close frequencies.

> 4.	Does it work under X Windows?  Linux people asked this (of
> course).  I said no, but let me know if you make it work under X
> windows.  Someone (I don't recall who) said he might try to do that.  I
> would think it would be very complex.
I know nothing about X-windows. I think you would need a much faster 
computer if you want to use the Delta44 at full speed. I do not think
there are any fundamental problems, Linrad uses very screen functions
and I am sure it would not be difficult to replace them by the
corresponding X-windows calls.

> 5.	Can it be rewritten in Microsoft Windows?  I said 'the source is
> available on Leif's website.  Good luck, and let us know if you
> succeed'.  I will not hold my breath until I hear back on this one from
> them ;)
I think this will be no more difficult than writing for X-windows but
I think there will be performance problems. I have a feeling Microsoft
allows other programs to use the sound channel simultaneously and maybe
that will cause problems.

> 6.	When are the other boxes coming out?  I said I do not know.
Hmmm, I do not know either. I have the first RX70 prototype running 
well now. Several major modifications were needed to bring down the
coupling between the channels so I am right now working on a new
layout. The time until the boxes come out is probably two months
for me to be happy with the designs, another 3 months to get all the
components (X-tal delivery time) plus another month for
production. No promises;-)

> 7.	Many, many times:  My machine is xxxxxxxxx.  Will it run Linrad
> OK?  I told them to all email Leif ;)  Only kidding.  I told them what
> has worked for me, and referred them to Leif's webpages.  I again
> reproduced Leif's webpages as well as mine and Bob Larkins on the CD for
> the conference.
The answer is: Any computer that has video that works with svgalib
and a sound system that is OSS compatible will work.

> 8.	What versions of Linrad will work?  Followed then by What
> version does Leif run?  I said RedHat, Suse, and Mandrake to the first,
> and check his website for the second.
What distributions of Linux will work? 
As far as I know all Linux distributions will work as long as
svgalib and OSS compatible sound works. 

73

Leif / SM5BSZ

LINRADDARNIL