Re: RF Help, Please!!!

Douglas Tourtelot wrote:

Hi David-

Do you believe that this is a small sample problem or are you looking at a recall?

Thanks.

D.

"Billy Sarokin" <bigmaho@xxxxxxxxxxx> wrote in message news:1142299736.621582.57950@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx


lol, 119 posts later a happy and successful ending!


Here's the latest... it *was* the problem I thought it was. Sure
enough, I put the receiver on the generator and the thing was clicking
like crazy. Then I sent it through service and tested it again.
Those new capacitors did the trick! It's _way_ quieter now. Service
is finishing up, and then it will be sent back -- no charge of course.

Yours...
David Thomas
Design Engineer
Lectrosonics, Inc.







Doug,
Here is David Thomas's earlier (13 Mar email which certainly made me feel better, being the owner of two 411's for my booms.)

I think I might know what this is! If it's the problem I'm thinking
of, it definitely sounds nasty, and the good news is that there's a
reliable test and an easy fix.

Recently we have become aware of a new failure mode in the IF chip
used in the 411. So far I have only witnessed the problem on two
(countem, two!) units, but on units so affected the problem was real
enough. The underlying problem is that the IF amp cannot gracefully
recover from very strong signals.

Typically we'd see the problem only in the range of 10 to 20 feet
operating distance. When a sharp null comes along due to multipath,
the RF signal strenth suddenly dips some 60 dB. A good unit rides
through that handily -- at close range, a 60 dB weaker signal is still
pretty strong. Operation should remain quiet and clean.
Unfortunately, units with this problem can't handle the sudden
weakening of the signal -- they "choke" as they revert to normal
sensitivity. The result is a nasty popping or clicking sound.

It is natural to blame the diversity system because its job is to
protect the receiver from the glitches caused by these deep nulls, and
in this case, the glitches are offensive. Oddly, the diversity system
isn't at fault -- the fix is to toughen up the IF amp so it doesn't
mind the normal fluctuations in signal strength.

We have a test set here at Lectrosonics where we can generate a
carrier with wildly and rapidly varying amplitude, simulating
multipath conditions. When the amplitude is set for the equivalent of
10 to 20 feet of range, affected units go nuts, making horrible
clicking and popping sounds. At lower (and sometimes higher) signal
levels, the symptom goes away.

I'd be happy to test your unit, and of course perform any repairs
necessary. As I said, this problem is fairly rare -- we've previously
encountered it in only two 411 units. However, I'd feel much better
to have the problem in ZERO units! The fix is to replace four
capacitors that are easy to access. Our service department swaps
these capacitors automatically in any units that come in for service,
just in case.

David Thomas
Design Engineer
Lectrosonics, Inc.



Regards,

Jim Rillie
.

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