>Hi Rich
>
>I have not read or seen data on the ALC overshoot problems. The ARRL
>reviews seem to politely ignore the issue.
** I see c. 20% overshoot on my TS-440S on the first syllable. Running
almost no ALC helps.
>My main interest in this area is
>too emit the cleanest possible signal. Its becoming a uphill battle to find
>a new model radio with a clean transmitter without ALC, key clicks and bad
>IMD problems.
** Without some form of ALC, excess IMD is a virtual guarantee --
unless the operator religiously rides herd on the mic gain comtrol.
>
>I have become sensitive to the problem because here in VK the bands are now
>awash with stations running these new Russians Tetrode Emtron amplifiers
>with low drive levels to achieve 400 watts output. The leading edge splatter
>and ALC overshoot is very common.
** The solution is to run just enough mic gain and adjust the drive
and/or grid-bias potential until no grid-current flows - especially on
the syllable that trips the VOX. .
>Another problem is that the RF actuated
>EBS in these amps are poorly designed, something you have mentioned in the
>past. It would not be such a bad problem if the rigs had good IMD and
>proper power control without overshoot.
** RF-actuated EBS is an idea that looks workable on paper but one which
doesn't work acceptably in practice because the EBS switches in and out
of non-linear bias during soft-syllables. Synchronizing the EBS with
the RF-relays is clearly the best approach - even though it requires two,
additional wires from the transceiver to the amplifier's RL Control
circuit. As I see it, even with a radio that had no overshoot and
pristine IMD, RF-actuated EBS would still have the problem of generating
IMD (and harsh-sounding audio) by rapidly switching in and out of
non-linear bias during soft-syllables.
>
>
>By the way hows your dummy load project coming along?
** The 50-ohm, 2 by 18 inch Type-SP resistor arrived from
Kanthal-Globar. Next step is a trip to the plumbing store for some
sewer pipe and 2 garden hose fittings for the water in and out
connections. I am going to build a 1500v-max 1000 to 1 voltage-divider
into the input to allow direct measurement of the peak RF voltage across
50-ohms with an oscilloscope. This is the only PEP measurement that I
trust after years of working in calibration labs..
>I have a 2 X 12 inch
>resistor sitting here that would probably work well. I will be waiting to
>see how your project goes.
>
** The 18-incher is probably overkill, but the new-price difference was
minimal.
cheers, Craig
>
>
>----- Original Message -----
>From: "R. Measures" <r@somis.org>
>To: "craig" <craigs99@iprimus.com.au>; " AMPS" <amps@contesting.com>
>Sent: Saturday, January 03, 2004 2:45 AM
>Subject: Re: [Amps] IMD & ALC's
>
>
>> ** Good one, Craig. One problem is trying to convince the ignorant that
>> mo' ALC is not mo' betta. Another problem is manufacturer's owners'
>> manuals which recommend using a certain level of ALC. - such as
>> mid-scale.
>> - Have you seen a study on overshoot level in various transceivers?
>>
>> >Here is a great link discussing the IMD performance of modern radios and
>> >poor ALC design. Some very interesting IMD measurements on some radios.
>> >
>> >http://antennspecialisten.se/~sm5bsz/dynrange/alc.htm
>> >
>> >Craig
>> >VK3HE
>> >
>> >_______________________________________________
>> >Amps mailing list
>> >Amps@contesting.com
>> >http://lists.contesting.com/mailman/listinfo/amps
>> >
>
>
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