[Amps] RF on audio using 374A
sub1 at rogerhalstead.com
Wed Sep 14 09:06:04 PDT 2011
On 9/14/2011 11:25 AM, Jim Brown wrote:
> On 9/14/2011 6:19 AM, Carl wrote:
>> Glad to hear it wasnt a Pin 1 problem Roger (-;
> Ah, but it most likely WAS a Pin One Problem,
As am I. It's just with the antenna imbalance every LED in the station
was close to full brilliance when I'd reach 1KW output let alone 1.5KW.
That made the pin one problem a losing proposition.
We talk about pin one problems but "I think" nearly *all* of today's
rigs are wired that way. That means conditions have to be just right for
them to work and "problems" are far more common than we realize. I was
listening to a couple of guys running SDRs the other night. They were
complementing each other on the quality of the signals and the ability
to be "right on" frequency. What happened to tuning so the other guy
sounds right? This is a family group so I can only say the one stations
quality was... welllll... not good. He had a real bad dose of RF
getting into the audio, yet instead of trying to ferret out the problem
the other station was telling how great he sounded.
"In the old days" I remember operating FD with so much RF floating
around you'd have to coordinate switching from transmit to receive
between stations to keep from getting RF burns, yet the receivers never
seemed to notice.
Now we have rigs that have capabilities and dynamic ranges we would have
never dreamed about back in those days, but even with 120 db dynamic
range they won't tolerate a little RF on the chassis just because ground
is no longer ground. By floating it they can add a few functions and we
have to sniff out the RF getting in.
My current rig, a Yaesu FTDX5000MP cost me more... More? It was almost
twice in actual dollars what my first new car cost, which was a Pontiac
Bonneville convertible. OTOH that was back in late 1961. Still, the
FTDX5000 which has a fantastic dynamic range, great digital noise
reduction, will not tolerate RF on the chassis.
NOTE: today's dollar is only a fraction of a 1961 dollar. To be a bit
more precise it's worth only 16 cents compared to that 1961 dollar which
makes that FTDX5000MP one of the cheaper rigs...Let me rephrase that...
One of the least expensive rigs I've purchased over the years. It's way
less than my old Hallicrafters ran and that station would tolerate a LOT
of rf on the chassis<:-)) Of course it also took a very strong back to
move the individual pieces. It definitely was not a station to set up
temporarily set up on a card table. IIRC RX = 76#, TX=92#, and amp = 113#
> and the choke to keep RF
> off the line was the easiest fix. Think, Carl, about HOW the RF on the
> coax shield gets into the equipment!
> The way equipment is built makes Pin One Problems more likely, AND very
> difficult to fix without a complete rebuild. So the easiest solution is
> to kill the current that excites the Pin One Problem, which is what
> Roger did.
> 73, Jim K9YC
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