Topband: Receiver problems.

[Tom Rauch]

>We know that radio that chokes with 9+30 (good "average" strong) signal
>few kHz away will also choke with signals that are spaced further away,

I'm sure you know what you are saying, but it came out wrong. 
The above usually isn't true. Many or most receivers today have 
much worse close-spacing than wide-spacing performance.

I think what you are trying to say is we know a receiver that is poor 
at wide spacing is always useless at close spacing, so we really 
want to know how it is at close spacing. If it is no good at close 
spacing, none of us want the thing!

Manufacturers should be reminded of this at every opportunity. I 
was very disappointed to see the new MarkV has poorer close 
spaced performance than a 1000MP (and a blanker-modified 
1000D). I'm leaning more and more towards a TenTec as the radio 
that can be modified to be a good contest and Top Band radio. It 
may have flaws, but I'd bet I can correct the flaws easier than I can 
update an old Drake by changing half the circuitry.

> load positioned to produce S9+30 signal on the RX with antenna on and on
> quiet band. Send bunch of dits and see how close you can get to TX
> frequency before you start hearing hash/crud on RX.

This tests the combo, and many of the problems today are in 
transmitters. Especially on SSB. The third order on a "good" 
modern SSB transmitter is typically -25 to -30 dB below one tone. 
Third order on a Collins KWM-2 I have here is -52 dB in the same 
test!  

 Don't be surprised to
> hear hash with just PTT on, without keying. That is your friendly and
> noisy synthesizer :-)

No, that isn't from the synthesizer Yuri. Noise without an actual 
output signal is from random noises in amplifier and mixer stages, 
it is very unlikely that local oscillators contribute to that noise. 

In my FT1000D, the bulk of that noise comes from a single FET 
used to provide an ALC control point! One single 15 cent part is the 
bulk of the "no signal" noise on the transmitter! I would gladly pay a 
dollar more for a radio with a better FET at that point.

A Ten-Tec Omni 6 I had here was stone dead quiet, there is no 
reason other rigs can't be.   

Synthesizer noise is present only when transmitting. The problem 
is we have no way of knowing it is in the receiver or the transmitter 
we are listening to unless we have a known quiet receiver to listen 
on. The Ten-Tec is very good in this regard, and unfortunately one 
of the most popular rigs on the band and used in contesting is not.

All of us know about the keyclicks we hear, and I think the ARRL 
needs to test transmitter keyed bandwidth. Few of us would object 
to paying a few dollars more so we don't bother our neighbors on 
the band, but it will never happen unless reviews start publishing 
useful factual information. 

Either we all go back to split operation, or we clean up the rigs.

73, Tom W8JI
w8ji@contesting.com


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