[Elecraft] ARRL Field Day

[Mark Petiford]

Bill's message brought a question to mind:

I am relatively new to PSK (operate mainly CW), but after receiving my KX3, started to take an interest in it.  After listening for some time, I became curious as to why some hams were giving out poor IMD reports and verbal reports of "You are splattering all over" when I wasn't always seeing the same thing.  Some folks were just downright rude with their reports.  I realize that different software packages may give different IMD measurements, but a few were grossly different.  There seems to be a lot of information about getting things set right on the transmit side, but not so much on the receive side.  Certainly, making sure the RF gain is down is important to keep all the amplifier stages linear, but little is ever mentioned about AGC.  It is similar to ALC on the transmit side, and is certainly non-linear if you are operating near or "through" the threshold (not sure I described that very well).  For those reasons, I would think that receiver
 AGC could also generate the IMD that these stations are seeing causing them to give out poor reports.  Admittedly, reducing RF gain helps to keep you from activating AGC, but seems like maybe turning AGC off before giving a signal quality report would be advisable.  Some of the comments I have heard have kept me from jumping into PSK with both feet.  They take the fun out of operating.


The website http://rsq-info.net/ has been most helpful, but I don't recall seeing any mention of AGC, so maybe I am completely off base here.  I am really a PSK novice, so any comments would be appreciated.  I haven't run any digital modes (except cw) since I sold my Model 19 TTY.  Back then, we didn't have an easy way to measure IMD or even see the sidebands that you see on a waterfall, and you almost couldn't hear the audio over the clatter of the Model 19 once you had your signal sync'd up.  We just operated.


Mark
KE6BB

  



________________________________
 From: Eric Swartz  WA6HHQ - Elecraft <eric at elecraft.com>
To: Bill Frantz <frantz at pwpconsult.com> 
Cc: elecraft reflector <elecraft at mailman.qth.net> 
Sent: Wednesday, June 26, 2013 10:16 PM
Subject: Re: [Elecraft] ARRL Field Day
 

Hi Bill,

Its much more likely they had wide band TX phase noise that was causing your problems. (Unless they were running K3s :-) There is not much on the receive side that you can do to eliminate that. 

Eric
elecraft.com
_..._



On Jun 27, 2013, at 3:37 AM, Bill Frantz <frantz at pwpconsult.com> wrote:

> The West Valley Amateur Radio Association field day operation was set up as it has been for the last few years on Mora Hill. Mora Hill is at an altitude of about 500' on the west side of the Santa Clara Valley, California. This year we were 9A SCV. We had 4 towers with various Uda-Yagi antennas for 20M, 15M, and 10M with wire antennas for 40M and 80M.
> 
> On HF we were an all K3 operation and for the second year in a row experienced no mutual interference between our transmitters. We did set up our antennas in a line, all pointed at the east coast, so the side lobe rejection helped reduce interference. I was operating the digital station for most of the event and the only indication I had of other stations in our operation was a strong track on the P3 from our CW operation.
> 
> I did get significant interference from another field day operation. They were set up perhaps 1/4 mile away in the major lobe of our antennas using 100 watts. When I turned the RF gain down low enough to prevent overload from their signal it looked like a clean PSK signal, so I think the wide-band interference was being generated in my receive chain. However, with the gain that low, I couldn't receive anyone else. :-)
> 
> The K3 I was using has 250Hz 8 pole and 2.1KHz 8 pole filters in addition to the 2.7 and FM filters. I could get the interfering station out of the passband on the 250 filter quite easily, but there was still a wide band of noise covering the entire 2KHz band of the computer waterfall. Using the notch filter didn't eliminate the noise.
> 
> In the end we had 139 digital QSOs in the log and many more CW and SSB ones. We all ended up tired and happy which means we had a good field day.
> 
> Does anyone have any ideas about how to improve reception under these conditions?
> 
> Cheers - Bill, AE6JV
> 
> ---------------------------------------------------------------------------
> Bill Frantz        |"Web security is like medicine - trying to do good for
> 408-356-8506       |an evolved body of kludges" - Mark Miller
> www.pwpconsult.com |