Topband: Receivers, Noise Blankers and Key Clicks

[Joe Wilkowski]

This is becoming more and more interesting.  I have to agree, the IMD
products in my FT1000MP provide anomalies in the form of clicks and thumps
continuously during a contest.   So, given that information, how is one to
discern if a transmitting station that appears to have key clicks on his
signal really has them if you are listening to the signal with a device that
also contributes to the problem (below) ? This obviously could explain the
number of click cops as well.

Interestingly ,  I usually have my R4C running in the background during a
contest and I can tune over a range of signals and not hear much of the
clicking and thumping I regularly hear with the MP.  Also, once I clamp the
MP's IF down to the 250 hz filter passband, it cleans up well but is not too
effective or productive when you are on a run frequency and folks are
calling you outside of your passband.

It seems the problem is also acerbated by the following fact.  There are
significantly more stations on the air using "state of the art" rigs during
contests than in past years.  Technology improvements  have drawn the masses
to the contesting environment creating real clicks in some cases as pointed
out and analyzed on this reflector  as well as perceived clicks caused by
modern receivers as indicated by recent posts.

A grass roots revolution seems to be the only answer if we are to expect the
radio manufacturers to pay more attention to the design.

/joe

----- Original Message ----- 
From: "Tom Rauch" <w8ji at contesting.com>
To: <jimjarvis at ieee.org>; <topband at contesting.com>
Sent: Tuesday, February 03, 2004 3:39 PM
Subject: Re: Topband: Receivers, Noise Blankers and Key Clicks


> Very interesting Jim. That's another good case the ARRL publishing
> close-spaced testing.
>
> > Depending on what signals are present within the 15KHz wide
> > roofing filter, what you hear can be anything from keyclicks
> > to 'thumps and bumps' from lowpass filtered keyclicks, to
> > a 'growling' sound on ssb...to the am detected envelope of
> > your signal of interest, injected after the product detector
> > audio.  Essentially, you're interfering with youself.
>
> The symptoms sound like what the FT1000's (and other Yaesu rigs) do except
> in them it is caused by IM products in a FET amplifier left hanging off
the
> IF system.
>
> If close-spaced dynamic tests were published in QST reviews, many of these
> problems would be corrected. Manufacturers will only test the parameters
> that get headlines in reviews, so the real key is getting the ARRL to
> publish close-spaced test data and occupied bandwidth data for
transmitters.
>
> The tests would have to be at 500Hz spacing on CW, not 2kHz. One new radio
> about to be released has a ~2kHz roofing filter making it have really
> inflated 2kHz test figures, but we really need 500Hz or less spaced
> performance data for CW.
>
> 73 Tom
>
>
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