[1000mp] Single band (80 meters) high swr problem

[Dan Kovatch]

Paul, this sounds like you're getting RF into the MP causing the foldback. I
would try a choke or bead balun between the mp and the amp. I have used
these to keep RF from getting back into  radios and fubaring things up.
There is(was) a documented 15 meter problem from Yaesu and this is detailed
on VA3CRs MP website-but no mention of it ever affecting other bands. The
fix involved adding some copper foil tape to insure a better ground and
changing some small inductors (If I remember right) I did only the grounding
and it fixed my MP on 15. I had lowered output when barefoot and full output
into  an Alpha 76pa (go figure!)
Good luck

Dan
W8CAR
Dan Kovatch
zone 4 and 8/ohio/EN81oj
www.geocities.com/w8car
www.geocities.com/w8car/classics
----- Original Message ----- 
From: <paule@sfu.ca>
To: <1000mp@mailman.qth.net>
Cc: <ve7sv@rac.ca>; <dale.green@aircanada.ca>
Sent: Monday, December 29, 2003 2:47 PM
Subject: [1000mp] Single band (80 meters) high swr problem


> This is a followup to my initial query regarding odd behavior on 80
meters.
>
> The problem is this. On 80 meters only (all other bands are fine) when
> transmitting into an alpha 86a amp, without the internal tuner engaged,
> there is a high swr indication that causes a power foldback which does not
> allow the amp to be driven to full output.
>
> Some additional data points since my first posting.
>
> The problem is the same with both antenna ports A & B on the MP.
>
> The rig seems ok in the ssb portion of the band, but the swr
> problem gets worse the lower in the band I go.
>
> Transmitting into a dummy load results in a flat swr and full output.
>
> The problem exists with two different alpha 86a's, both of which work
> fine with other rigs, and show no input swr problems with those rigs.
>
> It looks to me like there is an out-of-band radiation problem with the
> mp causing the high swr/low output problem.
>
> Unfortunately, I don't have a spectrum analyzer to determine exact
> frequency of the spurious radiation.
>
> Placing an ICE bandpass filter inbetween the rig and the amp allows
> full output.
>
> Employing the internal antenna tuner allows the reactance to be tuned
> out, resulting in full output.
>
> While the later two situations provide bandaide solutions, they are
> not dealing with the real problem which I would like to be able to
> fix.
>
> I suspect that playing with the line length between the rig/amp
> my bring the swr down, but again, this appears to be just a coverup
> for the real problem.
>
> Any other suggestions as to what I should look for.
>
> Have there been known failures of the bandpass filters? If so how
> difficult are they to repair?
>
> Thanks in advance.
>
> cheers, Paul - VA7NT ex VE7CQK - email: paule@sfu.ca
> "Those who hear not the music. . . think the dancers mad."
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