RadioBanter - View Single Post

April 20th 06, 03:01 AM posted to rec.radio.amateur.homebrew

wrote:

On Wed, 19 Apr 2006 17:42:35 GMT, "Michael A. Terrell"
wrote:

The engineers at my last job liked the Mini Circuits ERA and similar
monolithic amps. They also liked to do most of the AGC on the front end
rather than at the IF. This sometimes included an electronic attenuator
to drop the gain by 20 dB to prevent overloading a critical stage. The
customers liked the way they worked, they ordered plenty of them at
$20,000 USD each.

I tried that once using MAR-6s and -11s for gain and 1n4007s as
pseudo PIN diodes (Pi antenuators) between stages. Produced an
excellent IF for gain, noise and intercepts but it drew near 350ma
at 9V for the IF and AGC. Definately not for the qrp/battery user.

Allison

We weren't in the QRP business. We were building hi rel equipment to
track space probes.

Well that much was obvious. However, despite the higher power needs
it's performance is stellar. I can see no reason why it would not be
very high rel.

The reciever it was used in has a overload threshold and dynamic
range far higher than anything in the ham market. Also the NF is low
giving it an excellent MDS. It was built to work weak signals
effectively without overload because I have a "kilowatt charlie" less
than 300yds away on the same band. Nominal RF comming down
the coax from him is 25-150mw! The whole reciever pulls a whopping
2A (no signal) becuase of all of the high standing currents in RF and
IF processing never mind the required 17DBM LO..

At the other end of the power spectra I've used cascode J310 FETs
to build very good IFs with far lower power needs but still good AGC
and gain.

What's hard is building filters with at least 140db of stopband
attenuation. There nothing like shielding, lots of it. Then testing,
testing, testing.

Allison

We built tubular filters in house, because we couldn't get what we
needed, when we needed it. We built the ground station and a mobile
earth station with a large mobile diesel generator for power, for the
Italian government to track their launches. They had a severe overload
problem, trying to set up the one station near the launch pad.
Engineering was going round and round about a way to reduce the signal
levels prior to the launch, that could be done quickly. My suggestion
was a chain link fence near the pad to block most of the signal, till
the rocket left the pad and was no longer pointing right at the ground
based antennas. The receivers had lots of aluminum between stages to
stop stray signals.

We used a LINEAR AGC system that was a pain to get set up, but the
dual diversity combiner required the linear 0 to 5 volt signals to steer
the combiner.

--
Service to my country? Been there, Done that, and I've got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida