Jim
It is probably a good idea to throw away the coax switch.
The best isolation to unselected ports that you can expect would be on the
order of 30 or 40 dB
A bit of math and you see that you are jamming a lot of power into a
receiver front end that is designed for microwatts.
73
K6EXO
----- Original Message -----
From: Jim Reid <jreid@aloha.net>
To: <amps@contesting.com>
Sent: Tuesday, October 26, 1999 12:34 PM
Subject: [AMPS] RF Surge Problem
>
> Hi experienced ones,
>
> Not sure if the AMP reflector is the place for
> my questions, but don't know where else I
> could find someone who might have the experience
> to answer, hi.
>
> I had a call from the Service Center for Yaesu
> in Cerritos. I sent my FT-1000D to them just Friday;
> talk about instant service! The radio was delivered
> from Hawaii to them by Fed Ex Monday morning;
> the tech called Monday 4:30 pm PST.
>
> Anyway, he reports that for the second time, happened
> also last Summer, that I have managed to get enough
> RF into the rcvr front end to blow something called
> an RF Surge Protector. This is Yaesu P/N DSA-301LA;
> in August the invoice cost for this part was $2.52. Of
> course, it cost $90 each way from Kauai to Cerritos
> via Fed Ex, plus $75 labor to Yaesu!! Much the same
> is now recurring.
>
> I cannot find anything about an RF Surge Protector in the
> Yaesu manual for the FT-1000, nor in any of the diagrams
> in the back.
>
> Symptom I had was that the transmitter would not transmit,
> but the rcv section seemed just fine to me. Most power I
> could get out was about 12 watts on any band, and
> the vswr indicated very high, even with the radio terminated
> into a good dummy load. Certainly the high vswr is why the
> output power was so far cut back.
>
> Yaesu tech also asked if my QTH had suffered a direct/
> nearby lightening strike -- I assured him not.
>
> But something is wrong, as I am sure this same thing
> occurred a few years ago to my 950SDX, some little
> coil had opened in it, and would not xmit.
>
> I use an Alpha-Delta-4 switch with which I select between
> my Ten Tecs and Yaesu transceivers, and previously the
> 950SDX .
>
> So, if I am using the Ten Tec as the driver for the Henry
> amp, might there be some way for RF to get into the
> Yaesu, even when it is not turned ON, and has the
> A-D switch between it and the Ten Tec drive line.
> One note: I have not yet, but am today, running braid
> from my station ground system to that Alpha-Delta
> switch, was pointed out to me that that might be the
> problem. But, the A-D switches short the coax
> center conductor to the shield/ground when the
> position is not selected, right? So my center
> conductor from the Yaesu should have, at least
> been shorted to all the coax outer shields attached
> to the switch.
>
> However, I can't see how 80 or 90 watts from the Ten
> Tec, attenuated by whatever the isolation of the A-D
> coax switch might be, would be enough to blow the
> diodes protecting the Yaesu front end. Nor do I see
> how the output power of the Henry could get in there
> either.
>
> A strange situation. I can easily take the switch out,
> and just "hard wire" to which ever transceiver I would
> be using, but that does not seem necessary to me.
>
> It really seems to me that the Yaesu failed one afternoon
> while I was using it along with the Henry amplifier. But
> again, I cannot imagine how RF could get into the Yaesu
> and damage it when it is acting as the driver for the amp.
> I suppose the Yaesu might quit driving and open the rcvr
> while the Henry is still outputting energy? But how would
> that get back around into the input line to the Henry which
> is coming from the Yaesu driver?? Also, this "accident"
> may have happened while I was fiddling with the rig
> Processor and Drive/ALC knobs; could something
> backfire while driving the linear and adjusting these
> to blow out the Surge Protector?
>
> I guess I don't understand the Yaesu circuit anyway, as
> if the diodes are blown in series with the output FETs,
> how could they get blown by something coming in the
> rcv line without hurting the rcvr operation, which seems
> fine to me??
>
> Anyway, wondered if this was something anyone else
> has experienced using a linear? This could even
> have occurred while I was tuning up into the Bird load,
> I suppose. As I understand, you are to tune up using
> pretty high power, then back the drive back such that
> you actually will output only 1500 watts peak on SSB;
> this method is supposed to get you max linearity and
> lowest IMD products. So I have been tuning up at
> around 3kW into the Bird load. And separately,
> using the MFJ-250B gadget, to set up the
> antenna/antenna tuner to provide the 50 ohm load to the
> linear; certainly seems to work FB for me. Except maybe
> has caused my Yaesu problem??
>
> Any ideas, or maybe some electrical surge did get
> on my transmission line somehow....static, who knows!
>
> Does anyone sell an external "RF Surge Protector" which
> would go out, and I could fix/replace without another
> $257.52 cost incident? Must be some gadget like that
> to protect these expensive rigs.
>
> 73, Jim, KH7M
>
>
>
>
>
>
>
>
> --
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>
>
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