DTC hath wroth:

Jeff Liebermann wrote:
If you're thinking of impulse noise, you're mostly correct. However,
there are plenty of other sources of AM noise available. For example,
the typical VHF aircraft radio requires substantial filtering of the
magneto to avoid hash. Same with any onboard motor. If you've ever
tried to install a TV (VSB is a form of AM) in a vehicle, you'll also
find that ignition and motor noise can be a problem.

Dang it...my memory is slipping. What did Motorola call their noise
filtering circuit on their old low band Motracs. Extenders[tm]? As I recall
it was a simple noise blanker.

"Extender". It was a 2nd almost identical receiver, tuned to a nearby
empty frequency. If there was any impulse (ignition) noise, both
receivers would detect the pulses. The 2nd (Extender) receiver would
block the IF signal in the main receiver for the duration of the
pulse. This resulted in a "hole" in the receive IF and audio, but it
was far less noticeable than if the pulse were allowed to be heard.
The tricky part of the design was getting the delays nearly identical
in the two receivers. It also made the 80D/140D/Motrac/Motran radios
rather huge and heavy. Extenders were considered a "standard option"
on most Low Band (30-50Mhz) radios as this is where the ignition noise
is the worst.

The more generic term "noise blanker" applies to this scheme, as well
as a mess of others that detect in a single receiver or blank in the
IF or audio. GE decided that "extender" was a good name for their
mobile repeater, and called it a "mobile extender" or more commonly
just "extender".
http://www.mbay.net/~wb6nvh/chpradio.htm
Egads. I'm cleaning house and found a large box of 40 year old
Motrash control heads and cables. Want some junk?

There was also a scheme to eliminate ignition noise that involved
running a wire to the points on the distributor. The assumption was
that there was a substantial delay between when the points opened, and
when the spark jumped in the spark plug. This allowed the receiver to
be blanked before the noise pulse arrived, which really improved the
noise blanker performance. I was working on the design when marketing
decided that it should tilt at other windmills. Only a few prototypes
were built, were never patented or produced, and worked really quite
well. Cheaper too. That was all just fine because cars were begining
to use electronic ignition systems, which didn't have easily
accessible ignition points.


--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

Jeff Liebermann wrote:
Egads. I'm cleaning house and found a large box of 40 year old
Motrash control heads and cables. Want some junk?

Slacker...I tossed out all my old Moto stuff years ago. Last time I played
with the Motorola line was around the Micors came out. i used a few of them
for tower top UHF repeaters

DTC hath wroth:

Jeff Liebermann wrote:
Egads. I'm cleaning house and found a large box of 40 year old
Motrash control heads and cables. Want some junk?

Slacker...I tossed out all my old Moto stuff years ago. Last time I played
with the Motorola line was around the Micors came out. i used a few of them
for tower top UHF repeaters

The local hams still have ancient junk pretending to be repeaters and
such.
http://www.LearnByDestroying.com/k6bj/
I built most of it out of Micor mobiles and base stations. Since the
Micor stake pin connectors are chronically intermittent, there's a
large rubber hammer in each rack to bang on each radio to reseat the
connectors.

Since no sane person keeps such old parts around, I get to stock old
radios and pieces at my house. When the local comm shop cleaned out
their ancient Motorola parts pile, I ended up with most of their old
parts. I think it's time for a general purge, which means either eBay
or the scrap metal recyclers.

What I find amusing is that many police and fire departments rebuild
antique or vintage police cars and engines. They eventually want a
genuine Motorola twin coffin or 80D radio for the vehicle. I've
supplied about 4 of these radios (working) for various projects. The
first step is to spray the crumbling rubber insulated wiring with
clear acrylic to prevent further deterioration. Getting the radios
working is fairly easy as I have all the old test sets and some docs.
The fun part for me is watching the current crop of comm techs trying
to install the monster case in the vehicle. What do I do with all
this big fat cable is usually the first question.

--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558