[Elecraft] Seeting digital RX levels - was: ARRL Field Day

[Mark Petiford]

Good tips, Bill.  I appreciate your comments.


I think I will play around with two radios and do some measurements myself just to be sure I can believe in my own signal.  There is a pretty good guide to measuring IMD on rsq-info.net.  Once I make sure my TX side is clean, I can play with my RX side to see how if I can make a good signal look bad just for my own education.  That will be fun and educational as well.


Tnx again.

Mark
KE6BB



________________________________
 From: Bill Frantz <frantz at pwpconsult.com>
To: elecraft at mailman.qth.net 
Sent: Thursday, June 27, 2013 1:03 PM
Subject: Re: [Elecraft] Seeting digital RX levels - was: ARRL Field Day
 

As far as I can tell, the sound card is the limiting factor in 
receive IMD generation when using a K3, KX3 or K2. I try to run 
my receive just below where the computer software indicates the 
digital levels are distorting, and control that level with the 
RF gain control. This procedure seems to keep all the radio 
pieces within their linear range. I can see IMD being generated 
on my waterfall when I have the RF gain too high, and it is all 
in my receive chain.

Measuring IMD on a PSK signal is not as easy as it seems. Any 
band noise may be interpreted as IMD, so the weaker the signal, 
the worse the IMD reading. Ideally IMD measurements will be 
taken with a strong signal and without any data -- so you just 
have the PSK idle "railroad tracks". I just ignore IMD 
measurements from stations I am only receiving weakly, assuming 
they are also receiving me weakly. From strong stations, I get 
good reports.

As for obnoxious, rude reports; they aren't limited to PSK. I 
answered a CQ on 80M SSB running QRP and the ham at the other 
end just said, "Get an amp!" A signal report and a comment that 
I was too weak to continue the conversation would seem to be the 
least one should expect. I'll just try to remember not to behave 
rudely myself.

Cheers - Bill, AE6JV

On 6/26/13 at 11:45 PM, rv6amark at yahoo.com (Mark Petiford) wrote:

>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.

-----------------------------------------------------------------------
Bill Frantz        |Security, like correctness, is| Periwinkle
(408)356-8506      |not an add-on feature. - Attr-| 16345 
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