At the risk of being somewhat controversial ... why are we using ALC
these days?
I have many radios but currently use an FTDX5000 on 6m and transvert to
2m. None of my tube or solid-state amplifiers have ALC. Even on HF with
my trusty TL922 I do not use ALC.
My approach has always been to tune up the amp at full power on CW/FM,
switch to SSB, reduce drive to around 2/3rds. My 8877 on 6m produces a
very nice 1000-1100W with about 30-35W of drive. I can use plenty of
speech processing and a Heil headset with a "DX" element to create a
"wall of sound" type signal for contesting and yet the signal is narrow,
has almost no splatter and doesn't suffer overshoot or need ALC to hold
it back.
Basically I'm using the 2/3rds rule - most so-called "linear" amplifiers
are not... at best they're approaching linear for the first 2/3rds of
their output (to around 65-70% of their rated output) after this they
become increasingly RF compressors. The 1dB compression point on some
amplifiers is shocking.
I cannot see the point of (over) driving an amplifier and effectively
using ALC to "hold it back" ... it just seems to me that if you're doing
this then your amplifier isn't big enough in the first place - to this
end I have to say I'm with Mr. Measures... a 3CX3000 or 3CX5000
under-run at 1500W PEP is just going to be SO SO much nicer than a small
amp thrashed to within inches of its life ;-)
Leif, SM5BSZ, has done some work looking at an FT1000D's output and the
affects of ALC:
http://www.sm5bsz.com/dynrange/alc.htm
With solid state amplifiers things get more interesting again, since you
don't tune them up in the traditional sense. My experience with
building single and double BLF578 amps for 144MHz has shown that there's
a significant trade-off between gain, efficiency and linearity depending
which you pick to match on the load-line. Its the difference between
920W out at an apparent 73% efficiency (with poor IMD) or 800W out at
63% with good IMD... if you wan the magic kilowatt then use two of them
to get 1200W with each "loafing" at 600W.
The difference dropping from 1500W -> 1200W output is less than 1dB - a
fraction of an S-point but can make your signal 6-10 times cleaner and
reduce your electric bill.
I wonder how many people on here run their amplifiers at below the 1dB
compression point? and without ALC?
Mike G8TIC/M0VHF
On 26/07/2012 21:50, David Jordan wrote:
> Isn't this a really old concern? I remember having an FT-1000D where I
> noticed that instantaneous spike on key-down.
>
> I noticed in the menu of the Kenwood TS-480SAT you can select the response
> time of the transmit relay. I always thought that was Kenwoods approach to
> solving this concern?
>
> 73,
> Dave
> Wa3gin
>
> -----Original Message-----
> From: amps-bounces@contesting.com [mailto:amps-bounces@contesting.com] On
> Behalf Of Richard Solomon
> Sent: Thursday, July 26, 2012 4:39 PM
> To: amps@contesting.com
> Subject: Re: [Amps] Overdrive protection
>
> Not "all" of us know which they are ... is there a list somewhere of those
> rigs that exhibit this nasty problem ? Maybe if we boycott those rigs then
> the manufacturer will modify them.
>
> 73, Dick, W1KSZ
>
> _______________________________________________
> Amps mailing list
> Amps@contesting.com
> http://lists.contesting.com/mailman/listinfo/amps
_______________________________________________
Amps mailing list
Amps@contesting.com
http://lists.contesting.com/mailman/listinfo/amps
|