[Lowfer] rx setup

[Eric Smith]

OK -- thank you!  That all makes perfect sense.  I just didn't understand 
or even know that relationship.

I appreciate you all being so patient with me, and taking the time to 
explain these rudimentary details to the uninitiated!

Thanks,
Eric



On Sun, 16 Feb 2003, Lyle Koehler wrote:

> Regarding how the Argo display relates to the signal frequency, it's a long
> story, but here is a shortened version with a couple of examples for Argo
> build 132.
> 
> Argo *always* displays the audio frequency output of the receiver. However,
> under the Argo "setup" menu, there is a calibration feature that lets you
> correct for sound card errors, and which can also be used to adjust the
> displayed frequency scale so that it's easier to relate to the RF signal
> frequency.
> In all of the examples, I will assume that the receiver and sound card are
> precisely calibrated. That's a whole art in itself, but John Andrews'
> article on the LWCA web site provides a very good procedure.
> Let's also assume that we want to monitor the 185.300 "watering hole", and
> that the receiver has a digital frequency readout and a choice of CW, USB
> and LSB modes. CW mode is optional, but the receiver *must* at least have
> "SSB" capability.
> 
> Example 1: The receiver has CW mode, and a known "BFO pitch" setting, either
> digitally displayed or at a known fixed value like 700 Hz. This is the
> preferred mode of operation, but if the BFO pitch is unknown, you probably
> should skip to example 2 or 3! The reason I prefer CW mode is that the
> receiver display agrees (usually) with the signal frequency, and on many
> receivers, the narrow IF filters are only available in CW mode. On most
> modern receivers, if you're in CW mode, with a BFO pitch of nnn Hz (the
> exact value doesn't matter as long as we know what it is), when the
> frequency display set to 185.300 kHz, a signal on 185.300 will produce an
> audio output of nnn Hz. Suppose the pitch is set to 700 Hz. I would start
> with Argo in "full band" display, and then click on 700 Hz, to center that
> frequency in the horizontal display. It might require a few additional
> clicks within the Argo screen to get the frequency scale centered exactly
> where you want it. Now "WA", which is very close to 185.300, will appear at
> approximately 700 Hz on the screen. What about "WE" on 185.3026? Here is
> where it gets confusing. If your receiver uses the equivalent of USB mode
> for CW reception, "WE" will show up at 702.6 Hz. But if the receiver uses
> "lower sideband" CW reception, he will be at 697.4 Hz. On Icom receivers and
> transceivers, the default CW mode is lower sideband, so you will have to
> learn to stand on your head to read the display. Newer Icoms, including the
> R75, have a "CW-reverse" mode that puts things right side up, but Mike
> Staines has another sneaky way of doing this. He posted his technique to the
> Lowfer reflector, and I have attached it to the end of this message. Kenwood
> and Yaesu receivers (to my knowledge) use upper sideband CW reception as the
> default, so this isn't a concern. Suppose you would like to have the Argo
> display show the frequencies centered on 185.300, or wherever the receiver
> happens to be tuned? Go into the Setup menu, under Calibration, and type in
> the BFO pitch as a negative offset (-700 in the example we've given). Then
> WA will show up at 0 Hz, and WE will be at either +2.6 or -2.6 Hz, depending
> on whether the receiver is using the upper or lower sideband.
> 
> Example 2: The receiver BFO pitch is unknown, so we use USB mode. But if you
> tune to 185.300 kHz in USB mode, the audio output frequency of the receiver
> will be 0 Hz if the signal is at 185.300. In fact, any signal close to
> 185.300 will produce an audio output that is below the frequency response of
> the receiver's filters and audio system (and the sound card). No problem;
> you just tune *below* the signal frequency until the audio output is at a
> convenient frequency. I would pick something like 184.300, so that the audio
> output would be at 1000 Hz. That makes the arithmetic easy, and 1000 Hz is
> well within the passband of the system. WA will now show up at 1000 Hz; WE
> at 1002.6. Same procedure for "tuning" Argo, as in CW mode, except that we
> now center on 1000 Hz rather than on the BFO pitch. And if you want the
> display centered on zero, you can type in a -1000 Hz offset under the setup
> calibration menu.
> 
> Example 3: For some reason you want to use LSB mode. Now you need to set the
> receiver *above* the desired signal frequency, for example at 186.300 kHz to
> receive 185.300. The audio output frequencies will be inverted, so that WA
> will appear at 1000 Hz on the Argo display but WE will appear at 997.4 Hz.
> 
> Maybe these examples will clarify what the QST articles are trying to say
> about how USB, LSB and CW reception works on modern receivers...
> 
> And by the way, if you don't see anything on the Argo screen, it's perfectly
> normal. I ran two receivers (IC-706 and IC-756PRO) all last night on two
> separate frequencies with two computers, and got nothing but a couple of
> spurious signals. LowFER reception is not for the impatient!
> 
> Lyle, K0LR
> _________________________________
> 
> Mike Staines' procedure for producing a "right side up" display with an Icom
> receiver:
> 
> "Here's what I do for my 706...
> 
> When setting up the calibration I subtract the appropriate number to get the
> display to show "negative numbers".
> 
> A simple (but real) example:
> 
> When I want to RX on 185.3 I set the radio to WWVB, CW, and Argo to 30
> second dots. Then I go to "full band view" click on the trace for WWVB. The
> 30 sec/dot trace now gives me a frequency to calibrate against. Just now the
> frequency was 645.00 Hz.
> 
> Normally, I could go into "Calibrate" and enter -45. This would show the
> carrier at 600 Hz but still inverted. So what I enter is 945.00. this is the
> 645 of the carrier PLUS an offset that would put the display at -300.00. Now
> the number *IS* negative. But the scale is "upright". Lower freq carriers
> show up lower on the scale. A carrier on 185.299 will show up on -299, etc.
> 
> Sounds complicated until you actually step through it.
> 
> Mike
> wa1ptc"
> 
> 
> 
> 
> 
> 
> 
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