I have two homebrew, solid state amps with no alc. The big amp (1kW)
has no protection, uses MRF 154s, and takes 15 watts to drive to full
power. I have accidently driven it with 100 W with no damage. The
small amp (600 W) uses 4 MRF 150s in parallel pushpull. I built over
drive protection into that amp. It will not switch the amp into the
circuit if the drive is too high. This amp takes 10 watts to drive it
to full power. I have experienced over drive several times on this amp,
and so far it has faulted correctly. Having said all of this, I think
the best protection is an attenuator on the input so the exciter can put
out full output and not over drive the amp. With the Caddock film
power resitors available today, it should be easy to build a 6-dB, power
attenuator that could be inserted in the input of the amp. That would
be difficult to do on a commercial amp, however. The Quadra uses 8 MRF
150s and I believe it uses a 4-way power splitter on the input which
should offer some over drive protection with a standard 100 Watt
exciter. I believe the Ameritron uses an attenuator in its input. If
you wanted to add external protection, you could build an inline sampler
that prohibited keying of the amp if the drive was too high. You would
have to look at the hot key timing of the SDR to see if this would work
well.
Tom W0IVJ
Lux, James P wrote:
On 10/14/08 9:21 AM, "Lee A Crocker" <[EMAIL PROTECTED]> wrote:
My guess is a PTT feedback scheme would be too slow to save your bacon unless
it somehow anticipates the fault.
It would also depend on the PTT sensing logic in the software to work.
Crowbar across the RF input?
----- Original Message ----
From: Neal Campbell K3NC <[EMAIL PROTECTED]>
To: Bob McGwier <[EMAIL PROTECTED]>
Cc: Steve Nance <[EMAIL PROTECTED]>; Lee A Crocker <[EMAIL PROTECTED]>;
Flexradio <FlexRadio@flex-radio.biz>
Sent: Tuesday, October 14, 2008 12:06:56 PM
Subject: Re: [Flexradio] What would you like to see in an accessory box?
I think we have come to the same conclusion so there would be a PTT
line pass-thru and we will defeat it if the calibrated voltage is
exceeded (is exceeded t he right word for going too negative!)
Neal Campbell
www.abrohamnealsoftware.com
AIM:nealk3nc
On Oct 14, 2008, at 12:03 PM, Bob McGwier wrote:
VERY sound advice.
Bob
ARRL SDR Working Group Chair
Member: ARRL, AMSAT, AMSAT-DL, TAPR, Packrats,
NJQRP, QRP ARCI, QCWA, FRC.
"Trample the slow .... Hurdle the dead"
-----Original Message-----
From: [EMAIL PROTECTED]
[mailto:[EMAIL PROTECTED] On Behalf Of Lux, James P
Sent: Tuesday, October 14, 2008 9:04 AM
To: Lee A Crocker; Flexradio
Subject: Re: [Flexradio] What would you like to see in an accessory
box?
On 10/14/08 12:21 AM, "Lee A Crocker" <[EMAIL PROTECTED]> wrote:
I do like the idea of being able to plug the flex wire into the box
for
PSDR
connectivity independent of ddutil. I have at some times had
stability
issues
with ddutil and would like another path into the box. Also I would
like
to
see an output that would be compatable with previous X2 interfaces
Do you really think this will be fast enough to do ALC? If you are
going
to
use this to "protect" your amp it has to be virtually failsafe.
Trust not protection to a software implementation on a PC. If you're
really
worried about overdriving an amplifier, then you need a hardware input
limiter of some sort. There's just too many things that can go
wrong in the
PC environment (oops, it just hung, my protection loop froze..).
Remember
that the dttsp core has to get an input from the ALC signal, and
then go in
and adjust the gain, which then changes the levels of the signals
emerging
from the DAC.
Software is ok for this kind of thing, but you want it running in a
dedicated processor (e.g. That PIC).
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