I wouldn't be so fast to interpret Lee's 2 dB increase in IMD as being
*caused* by the ALC. In fact, the IMD he saw with no ALC may have been
inherent in the sound card to begin with and by slightly reducing the peaks
and increasing the average, the low-level 'grunge' that was already there
was brought up by 2 dB. Given the test apparatus, the accuracy would be a
bit suspect, but the test did show, in my interpretation, that there was no
'significant' increase in IMD as a result of using ALC. The really terrible
signals you see on the waterfall display are most likely a result of
overdriving the audio stages of the transceiver and/or RFI.
IMD on those old Collins rigs my have been low, but it came at a price.
Adjusting for inflation, a 1967 KWM-2A cost around $20,000 in today's
dollars. You could by five Orion II's for that price!
Ron N6IE
www.N6IE.com
(Formerly N6AHA)
----- Original Message -----
From: "Dr. Gerald N. Johnson" <geraldj@storm.weather.net>
To: <tentec@contesting.com>
Sent: Saturday, December 30, 2006 8:57 AM
Subject: Re: [TenTec] PSK-31 and ALC
While the intermod levels with lots of ALC aren't horrible by solid
state standards they aren't very good either. Remember the 32S-1 from
Collins did at least 10 dB better with tubes 50 years ago.
Your test do show an increase in intermod products with the increase
drive which is as I'd expect. Typically the ALC threshold is set at the
power that begins to show such increased intermod products.
--
73, Jerry, K0CQ,
All content copyright Dr. Gerald N. Johnson, electrical engineer
_______________________________________________
TenTec mailing list
TenTec@contesting.com
http://lists.contesting.com/mailman/listinfo/tentec
|