[Amps] FCC Denies Expert Linears' Request for Waiver of

Tue Jan 3 21:41:16 EST 2017

Sorry for writing too much lately, I usually am a "lurker".

Question:  I have no experience with "IMD meters" that are designed around 
measuring the IMD products of PSK AFSK inputs.  I get the idea of how they 
might work (famous last words)  but I am curious as to how they would 
compare to conventional designs using two tone tests where the audio sources 
are carefully isolated, and the measurement devices have the attenuator set 
to remain in the linear range without putting the products down into the 
noise floor.

My attempts have always resulted in: "Ok, this is better, and this is far 
worse", but I have never been satisfied that I have something like a TOI 
number that I can quote.  The premise that I can purchase something like 
this that gives accurate results with a simple AFSK input is attractive, but 
I have questions as to its accuracy.

A lot has been said here lately regarding IMD and how ALC can influence it, 
etc .  My limited experience measuring it has led me to doubt my own 
results, at least with ham radio devices.

Following advice is great.  Measuring it and seeing it with your own eyes is 
better.

What are the experts best suggestions in this regard?

Thanks.

Mark

----- Original Message ----- 
From: "Kevin" <kstover at ac0h.net>
To: <amps at contesting.com>
Sent: Tuesday, January 03, 2017 7:13 PM
Subject: Re: [Amps] FCC Denies Expert Linears' Request for Waiver of

> Jim,
>
> My TS-520 does not have a "power control" like my K3. My fathers TS-450SAT 
> does have a power control. I used to use the 520 on PSK31 and MFSK. I'd 
> tune it for maximum smoke on SSB and then feed it negative ALC voltage 
> from a 9V battery through a pot to control output power. Get it right down 
> to 25W and the IMD readings from my IMD meter would be -35 or better. I 
> did AFSK RTTY the same way.
>
> I assume the reason it worked so well was because the ALC voltage did not 
> vary with the transmitted signal. Otherwise it was a royal PITA messing 
> with the drive control, carrier control, and mic gain.
>
>
> On 1/3/2017 4:55 PM, Jim Thomson wrote:
>> Date: Tue, 3 Jan 2017 13:31:37 -0700
>> From: MU 4CX250B <4cx250b at miamioh.edu>
>> To: jim at audiosystemsgroup.com
>> Cc: "amps at contesting.com" <amps at contesting.com>
>> Subject: Re: [Amps] FCC Denies Expert Linears' Request for Waiver of
>> 15 dB Rule
>>
>> I remember that with the Drake C-Line, some ops would short the T4XC
>> ALC line, which would increase the power output to 175W. Most vacuum
>> tube transmitters I am familiar with did not have a power adjustment.
>> Even the mighty solid state Collins KWM-380 lacks a power adjustment.
>> 73,
>> Jim w8zr
>>
>> ##  I owned several new C lines.... and you wont get any 175 watts out of 
>> any of them
>> with the ALC shorted out. All that shorting out the ALC line did...was 
>> increase the talk
>> power a whole bunch on ssb.   Pep out stayed the same.  Average went way 
>> up.
>>
>> ##  For ALC between the xcvr and amplifier in question to even work 
>> correctly, the
>> time constant in the xcvrs  alc  has to match the time constant in the 
>> amps  alc circuit.
>> The drake L4B wont work with the Drake TR7.   Ditto  with a drake L7 and 
>> a drake
>> T4XC.   An  ALC  cap has to be swapped out to a different value in both 
>> those amps.
>>
>> ##  T4XC  + L4B  require no cap changes, alc is matched  for time 
>> constants....
>> ditto with TR7 +  L7.
>>
>> ##  If the amp in question doesnt have adjustable ALC,  it still wont 
>> work properly.
>> Both the L7 and L4B have adjustable alc.  There is NO power output 
>> control on the drake
>> T4X series, nor the TR3 /4 series.   The adjustable ALC on the drake amps 
>> was the only way
>> to tweak the po of the exciter.
>>
>> ## there were several of the kenwood  SS xcvrs, like the  TS-450 I 
>> believe  that had no PO control.
>> They ran flat out.... so again, if driving amp, the alc line to the amp 
>> had to be installed..and the amp had
>> to have adjustable alc.
>>
>> ##   back then using a xcvr that put out 130 watts pep, with an amp that 
>> required 100w of drive would work
>> fine, with the alc line installed and tweaked correctly.   The problems 
>> started when some bozo tried to use his
>> swan 500-700 CX to drive a SB-200,  or  8877,  then  try and rely on the 
>> alc connection between em..to keep things
>> under control.   Didnt work.
>>
>> ##  even on the older  SS xcvrs that had no PO control,  you could still 
>> control the output on ssb mode, by inserting
>> a low value of  dc voltage on the alc buss  on the back of the xcvr.  -9 
>> vdc  from a battery, through a 50k pot, tweaked
>> correctly works just fine.  Then you can dial up exactly how much pep out 
>> u want on ssb mode.   You have already
>> developed the ALC voltage.   Scream all u want, but you wont exceed 
>> say.... 65 watts, or whatever its tweaked to.
>>
>> ## another method is to use limiters and distortion cancelled clippers in 
>> the audio chain, results are the same.
>>
>> Jim   VE7RF
>>
>> _______________________________________________
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>> Amps at contesting.com
>> http://lists.contesting.com/mailman/listinfo/amps
>>
>
> -- 
> R. Kevin Stover
> AC0H
> ARRL
> FISTS #11993
> SKCC #215
> NAQCC #3441
>
>
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