AGC
 

Radio Shack used to sell two different models of wireless frequency
counters.I have a big Radio Shack catalog around here somewhere they
gave me at the store at Metrocenter Mall in 2001.The catalog does list
them in there.Has anybody ever used any frequency counters similar to
that before,are they any good?
cuhulin

AGC
 

"Michael A. Terrell" wrote in message
...
Tom Holden wrote:

"Michael A. Terrell" wrote in message
...
What do you consider "Fast" or "Slow"? The receivers we built had
seven different AGC time constants, up to 10 seconds.

.01 ms
.1 ms
1 ms
.01 second
.1 second
1 second
10 seconds

Michael, what receivers were these and why such incredibly fast AGC?
I assume these are release speeds; what were the corresponding attack
speeds?

Microdyne 700 series, and other lines like their 1100, 1400 and 2800
series. They were telemetry systems, and they were typically used in
diversity mode so you needed the fast AGC for some applications. They
had matching integration times for attack and release. I should know, I
tested hundreds of the boards on the bench while using a time interval
counter and calculating the reciprocals on the slower ranges. :(

Equal attack and release times over the entire range seems so
unconventional, at least for HF, MF, LF radios. I see the Microdyne 700 is
VHF/UHF and does not support AM. Fading at VHF/UHF line-of-sight is probably
very different than for ionospheric propagation as are the modes supported
and the fact that a human is not decoding the output.

From my readings, it seems that Fast Attack (less than 10 ms and closer to 1
ms often touted) was preferred for HF/MF/LF AM/SSB with selectable Release
speeds from a few tens of ms to over a second. After experimenting with AGC
modifications with that design objective, I'm inclined to think that the
Attack should be proportional to the Release, say, 10-20 times faster, not a
constant 10 ms. A really fast attack and really slow release combo resulted
in a single impulse of interference knocking gain down for a long time.
Equal attack and release speeds when too slow result in ear-damaging swells
of volume or unmanaged bursts of interference.

What do you think?

Any idea what the attack/release speeds are on your SW radios?

Tom

AGC
 

Tom Holden wrote:

Equal attack and release times over the entire range seems so
unconventional, at least for HF, MF, LF radios. I see the Microdyne 700 is
VHF/UHF and does not support AM. Fading at VHF/UHF line-of-sight is probably
very different than for ionospheric propagation as are the modes supported
and the fact that a human is not decoding the output.

From my readings, it seems that Fast Attack (less than 10 ms and closer to 1
ms often touted) was preferred for HF/MF/LF AM/SSB with selectable Release
speeds from a few tens of ms to over a second. After experimenting with AGC
modifications with that design objective, I'm inclined to think that the
Attack should be proportional to the Release, say, 10-20 times faster, not a
constant 10 ms. A really fast attack and really slow release combo resulted
in a single impulse of interference knocking gain down for a long time.
Equal attack and release speeds when too slow result in ear-damaging swells
of volume or unmanaged bursts of interference.

What do you think?

Any idea what the attack/release speeds are on your SW radios?

Tom


The Microdyne equipment was used all the way to KL and KU band and
for a lot of different applications including tracking space probes for
NASA. They are used mostly for long range digital data collection so
they are a very different from common receivers. One thing that was
different was that they used a fully linear AGC control system, rather
than the common logarithmic. I don't have all of the manuals. Due to
the RDAs that I signed I had to leave them all behind. All I have
manuals for is the C-band receivers they built and sold to CATV systems
and TV stations.

As far as the SW receivers at hand, I haven't tested any of them on
the bench. I lost most of my test equipment during the hurricanes over
the last few years when water got into my shop. The only receiver that
works at the moment is a DX-375 and possibly my HP 312 Frequency
Selective Voltmeter. I have a X-30 that was butchered by a hack at a TV
shop. He really messed it up trying to pick up Rush Limbaugh on SW
rather than listen to him on a local talk radio station. Another
receiver is a classic. A National NC183R that is going to be completely
restored. First, I have to finish repairing what little test equipment
that I can, and replacing the rest.


--
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