SV: [AMPS] Mission Impossible

sm5ki sm5ki@algonet.se
Mon, 06 Mar 2000 19:31:00 +0000


Hej Peter: 

In the TS950 two-tone test in QST 1/1991 distorsion is abt 42 dB below pep
for 3rd order mods. Higher order mods are also very low. This was worst case
measurment and on most bands it should be even better. However, I cant see
how much ALC was used in this test? Maybe no ALC? This rig usually sounds
very clean. 

I think the problem is behind the microphone as 150 watts pep is avaiable
and there is a possibility that too much drive was used for the finals. One
has also to know how the ALC from the amp was connected and used etc. Did
they use clipping and did they know how to use it properly? Maybe talked to
close to the microphone which in some differential pressure electret
microphones leads to distorsion. Do you remember when the ICOM SM2 first
came out? Boerge who worked for Bruel/Kjaer quickly found out, you could not
talk close to that microphone without getting very bad speech quality. This
has of course nothing to do with splatter outside the passband.

Hej daa de Hans


----------
>Från: Peter Sundberg <sm2cew@telia.com>
>Till: measures <2@vc.net>
>Kopia: amps@contesting.com
>Ämne: RE: [AMPS] Mission Impossible
>Datum: mån 6 mar 2000 17.13
>

>
>At 07:55 2000-03-06 -0700, Rich wrote:
>>>Checking the web pages out shows these stations run FT1000MP's, FT1000D's,
>>>TS-950's, Alpha's, Henry's, you name it.
>>>
>>Peter -  'This has got to be an amplifier adjustment problem.  The radios 
>>you mentioned are fairly clean.  
>>
>>cheers.  
>
>This is what puzzles me, but there is no doubt that "fine" radios can turn
>into mean machines if they are improperly adjusted. Many of the signals
>heard over the weekend had the sound to them that you get from setting the
>bias too low. I suppose this could be in either the exciter or the
>amplifier but it must be the easiest thing to check for most amateurs. Then
>again, one would have to find out what the ZSAC should be..
>
>I have been making some test with a good friend of mine re the behaviour of
>the FT1000D when driven beyond the ALC top level. IMD products 3.5 kc away
>from from the ssb carrier frequency rises about 10 db just by letting the
>ALC needle swing a little higher than recommended. This test turned out
>equal on two FT1000D's, driving different types of amplifiers. There is no
>doubt that even the FT1000D needs full attention not to sound bad.
>
>Listening to the microphone freaks on 14178.00000 in the mornings will tell
>you that the TS950SDX will splatter, check "Your Friend's" signal out and
>you will hear quite a lot of hash down the band. And they think they have
>the best audio achievable on SSB. Well they might (if you like the sound
>and want to spend 10.000 USD on a mixer/microphone), but out of the
>passband there is trash. Trash that their friends who want to operate close
>to the frequency will have to listen for NO reason.
>
>So Rich, it could be the amps, it could be the transmitter, but I'd go as
>far as to say it is the transmitter that makes the signal sound bad in most
>cases. (Or should we say the combination, to be politically correct..)
>
>Ciao,
>
>Peter/SM2CEW
>
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