FW: RE: 2 questions (Leif Åsbrink Oct 14 2002)

[Leif Åsbrink <leif.asbrink@xxxxxxxxxxxxxxxxxxxx]

-----Original Message-----
From: owner-linrad@xxxxxxxxxxxxxxxxxxxxx
[mailto:owner-linrad@xxxxxxxxxxxxxxxxxxxxx]On Behalf Of Leif Åsbrink
Sent: Monday, October 14, 2002 1:32 PM
To: linrad@xxxxxxxxxxxxxxxxxxxxx
Subject: RE: [linrad] 2 questions


Hi Roger,
 
> First, I am preparing powersupply for the WSE RX2500.  It takes +/- 15
> volts at 0.6 amps as I recall.  But I would like to have powersupply
> built now to accommodate future needs of 10.7 to 2.5 MHz converter and
> 144 70 MHz and 70 MHz to 10.7 MHz converters.
> 
> I had planned to have supply capable of +15 and -15 V at 1.5 amp each.
> Is this likely to be sufficient for the entire set of converters?  If
> not what do you recommend?

No. 1.5A will not be enough. The 70 to 10.7 is not finalized. I will receive
the first prototype PCB from Bulgaria this week and then I will investigate
the sideband noise characteristics. There is some risk that the RF amplifier
will dominate as the source of sideband noise, if that is the case I will
have to use a faster MOS-FET and that might lead to some change of the 
current needed. The present 70MHz design is ok for linearity but the
prototype does not have the right X-tals, it uses a frequency multiplier 
chain so I know nothing about what sideband noise levels can be achieved.
Each unit needs "about" 0.6 amperes. The power supply should be capable
of supplying 2.5 amperes for the complete 144 MHz receiver. In case you
want the same performance on the HF bands you may need some more unless you
mount relays to switch off the converter(s) not in use. 

> I believe the 10.7 to 2.5 MHz converter also will need other voltages.
> Is this true, or will it require just + and - 15 V and obtain the other
> voltages internally.
Only +/-15V. The "power" amplifiers operate directly on this voltage
with RC low pass filters while everything else has 78xx series regulators.

The units have carefully decoupled and filtered DC inputs so the power supply
does not have to be very good. I do not know at what voltage the units may be
damaged, but it is well above 15 volts. Feeding from +/-24 volts makes the 
units dissipate neary 30W but I do not think anything will be damaged.

The electrolytic capacitors are rated 25V, going above that is risky.

Nothing dramatic will happen if the voltage is reduced to about 13V. The IM3
performance will degrade slightly. Somewhere around 7 volts the LO will
stop oscillating.

> I would like to have both my homebrew receiver and The Time Machine
> plugged into the Delta44 with one using inputs 1 and 2 and the other
> using inputs 3 and 4, and I was hoping to be able to use the 'U' command
> to select appropriate dsp / audio devices to allow this.  Then I would
> have linrad setup in one directory to use 1 and 2 for homebrew receiver,
> and linrad set up in another directory to use 3 and 4 for The Time
> Machine.  Then I wouldn't need to keep plugging and unplugging cables.
> This is the physical laziness part.
Understandable. Channels 1 and 2 is trivial.
To run in another directory with channels 3 and 4 the easiest way is
to modify the code. You select two channels as usual in the "U" function
but in the open_audio_input routine you open with four channels
always. Then change the read statement in fft1 to read twice as many
bytes into some scratch area. Finally throw away half the data when moving
the correct number of bytes into the normal read buffer.

> But my first 8 or so guesses as to which of the MANY dsp choices
> possible to use (as listed in the 'U' command) did not give a solution
> that had inputs 3 and 4 being used so that proper output from Linrad was
> obtained. Do you know off hand if there is a combination that will allow
> inputs 3 and 4 to be used in this manner?  This is the mental laziness
> part; I thought if you knew the answer, and if the answer was that this
> will not work, then I could save myself the time spent to research all
> of the other choices.
I have no idea if you can select another of the MANY choices to do it
easier. Try OSS support - they should know.

73

Leif  /  SM5BSZ





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