Re:bad mixers exist


From: Robert J. Gobrick (
Date: Thu May 29 1997 - 00:52:43 EDT

Jeff, Paul and QRP-L Gang,

I've been following the thread on Jeff's "blown" SBL-1 on his Index Lab
QRP+. Having owned a QRP+ and having had it back to the factory twice back
in the early days before I returned it to the factory for it's final stay
(I was refunded my purchase) I will have to go along with Jeff's hunch that
it was a blown SBL-1 that was the problem.

For what ever reason Index Labs had a design problem which I was never able
to understand with SOME of the SBL-1 mixers and SOME of the QRP+ rigs. The
feedback that I got was that the problem was a static discharge off of my
long wire antenna that took out my first SBL-1. Index suggested at that
time that they were looking into a mini gas discharge protection circuit.
But I suspect what it really turned out to be was a timing problem in T/R
switching circuit that "allowed" some high level (5 W) RF to reach the
mixer and fry it (Larry East- is that possible). I believe this is what
happened on my second visit back to the factory since I "lost" it during a
turn-over to a station I was talking to (ever wonder why someone you talk
to on CW just disappears - hi).

Anyway WE do know that the QRP++ went to a hardier mixer (Synergy Microwave
Corp) to overcome the "dessert storm" effect but I was never comfortable
that everything was still OK. I will have to say that I have talked to
many QRP+ owners who have never had a problem and are happy campers. And I
also have to say that I have experienced the static discharge problem in
the past with other rigs - I used to wonder why I would see a little light
coming out of my turned-off Icom R-71 receiver - turned out Icom had a
little neon discharge bulb across the antenna input that would "glow"
during stormy weather.. if I only knew what that was ... Also when I was
in Newfoundland I used to hear my MFJ tuner make popping noises which I
account to the dry "ion" charged storm winds blowing across my long wire -
neat sound ..pop..pop...pop (never did want to look inside - hi)

Anyway Jeff, I think you and your friend solved your problem by replacing
the SBL-1. But I won't guarantee that the problem won't happen again -
Follow the advice that Larry East W1HUE writes in his two part QRP ARCI QRP
Quarterly article for QRP+ mods.

Also Paul, I was wondering if you guys in that nice dry climate in New
Mexico experience any of the "desert storm" static problems. When I had a
5/8 wave vertical mounted on top of my VW Van tied into my old Icom IC-27
two meter rig and after a few hours of high speed driving in the VW
(oxymoron) I would get so much de-sense to the rig that the only cure would
be to stop (easy to do in a VW) and go out and short (discharge) the Larson
whip to the Van body to start afresh.

Enough rambling - cheers 73/72 Bob N0EB

| |
| Bob Gobrick - N0EB & VO1DRB (ex WA6ERB, VE2DRB) Stillwater, MN |
| Internet: |
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