[Lowfer] ARGO

[John Andrews]

Doug,

Just to split a couple of hairs:

You need a known audio frequency to calibrate the sound card sampling rate. An audio tone from a receiver that depends on a converter L.O., and one or more conversion oscillators (and maybe the BFO) doesn't qualify. 

The combination of the converter and receiver likely has a frequency offset that varies with receiver tuning. Calibration of that offset at 60 kHz may be in error at other frequencies. 

The above applies to fussy situations like WOLF and slow PSK modes, where sampling rate must be nailed to keep framing consistent, and receiver offsets nulled out.  For QRSS use, you'll likely see cal errors between bands, and they MAY be small enough to ignore. 

John, W1TAG



On Dec 31, 2012, at 2:43 PM, "Douglas D. Williams" <kb4oer at gmail.com> wrote:

> Hi Mike. My method for calibrating ARGO is very simple, and does not
> require any extra equipment. As someone else pointed out, first you have to
> know the BFO sidetone of your receiver. Most modern receivers allow you to
> vary this sidetone through some sort of menu. I happen to like to hear a
> 700Hz tone when listening to CW, so that's what I keep mine at. I tune to
> 60 kHz WWBV with the receiver set to CW mode (reverse CW for Icom
> receivers), and allow the receiver to warm up for an hour. If you are using
> an upconverter, then simply tune to the converter's LO frequency + 60 kHz,
> so in my case that would be 3.060 MHz. At this point I would set Argo to
> some relatively fast QRSS speed such as QRSS10, and center 700Hz on the
> right side scale. You may have to reduce the receiver's audio gain and
> lower Argo's sensitivity slider quite a bit because WWVB is very strong in
> the lower 48. If your total system calibration is within 20Hz or so of
> being correct, you should see a bold, thick line start scrolling across the
> screen, with thinner lines (sidebands, I guess) above and below it. What
> you want to do is go into Argo's setup menu and choose Calibration. If you
> see the bold line at, say 705Hz then you would enter 700 (if that's the
> sidetone you are using) in the Measured frequency box and 705 in the
> Displayed frequency box. That should get you within one Hz of being dead
> on. You can dial it in even more at the slower QRSS speeds by using decimal
> places in the numbers you put in the Displayed frequency box.
> 
> What you are doing is calibrating the total receive system (receiver,
> upconverter, computer sound card) to be correct on the Argo screen. Of
> course, the job is easier if the oscillators in your receiver and
> upconverter are close to the frequency they should be. If you are using an
> upconverter with one of those little 4 MHz crystals about the size of a
> child's fingernail, good luck. ;-)
> 
> At this point, many people go a step further because they like to have
> Argo's frequency scale (the one on the right) display the actual frequency
> (in Hz) that they have the receiver tuned to. This can be accomplished by
> using the Offset box in the Calibration window and typing in the frequency
> you have the receiver tuned to, minus your BFO frequency, if I remember
> correctly. I'm usually too lazy to do this, so my screen captures tend to
> just have the BFO sidetone frequency.
> 
> Well, that was a lot of typing to describe something that generally only
> takes about five minutes to do, once the receiver is warmed up. ;-)
> 
> 73, Doug KB4OER
> 
> On Mon, Dec 31, 2012 at 1:58 PM, Mike Sanders <k0az at centurytel.net> wrote:
> 
>> Stan, Charlie and Mark, Thanks very much for all your input.
>> I am going to continue to follow through with this until I get it.
>> Your help may make the difference.
>> I am also using a converter and it is introducing minus 302 hz
>> of aggravation from the LO. My first lowfer target is WMS only
>> about 170 miles South of me.
>> I have not looked through all your email info yet but will as well
>> as checking out John's write up on ARGO set up.
>> Thanks again and you will know when I get a good capture.  73
>> 
>> Happy New Year
>> Mike Sanders
>>      K0AZ
>> 
>> 
>> 
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