[Yaesu] Single band (80 meters) high swr problem

Sat, 3 Jan 2004 12:05:13 -0500

Gee Guys...  We do not have any of those problems running QRP...  I guess
there is more than one advantage to QRP.

Happy - Healthy New Year

Jerry
W3CDE

----- Original Message ----- 
From: "Jim White, K4OJ" <[email protected]>
To: <[email protected]>
Sent: Friday, January 02, 2004 11:30 PM
Subject: Re: [Yaesu] Single band (80 meters) high swr problem

> First off, I think most manufacturers discourage the usage of the
> internal tuner when you are driving an amp - the input circuitry of the
> amp should already be looking like a nice 50 ohm load to your rig - and
> attempting to use the tuner to treat the amp as an antenna system means
> you are asking for troubles!
>
>
> Try this:
>
>
> a) WITHOUT THE AMP CONNECTED TO IT
>
> ...hook output of the transceiver into a 50 ohm dummy load.
>
> See if it is flat across ALL the bands... or about the same very low swr
> on all the bands (seeking to eliminate xcvr as having the problem). NOTE
> YOU SHOULD NOT BE USING THE INTERNAL TUNER!!!!!!
>
> You are going into a 50 ohm dummy load and absolutely no tuner
> enhancement should be needed whatsoever!
>
>
>
> b) after doing this and assuming you find everything is fine (note -
> again the AMP  IS   NOT   JUST   TURNED   OFF   BUT OUT OF THE LINE
> ALTOGETHER!)... put the amp back in the line but do not turn it on, i.e.
> if the t/r relay in the amp is not energized since it is shut off and
> that xcvr rf should be just passing through the amp on its way to the
> dummy load again.
>
>
>
> c) IF things still seem fine, ensure that the SWR readings are still
> flat on ALL of the bands, they should vary very little from those with
> the amp not being in between the rig and the dummy load... YOU ARE
> verifying the amp is transparent when turned off...
>
>
>
> d) if you turn on the amp and then realize problems, my guess is that it
> is some sort of input circuit problem, but it could be something else....
>
> If it is only one band that is a mess, open up the amp (no power of
> course) and check the path of the RF for that band... frequently a
> switch contact that changes the point where you tap into a coil is
> bad... sometimes the lower frequencies will use coils in series so if it
> is an 80 meter problem I would suspect 160 is also screwed up.
>
>
>
> If none of your problems have reared their ugly heads... the rig and
> xcvr are fine - it is an antenna issue, perhaps a bad coax switch wafer
> and while you are in the 80 meter position it may be trying to run both
> the 40 and 80 meter antennas since the wafer is out of alignment or
> somesuch... if you have splices in the feedline try moving the dummy
> load away from the rig a splice at a time to see where things go bad
>
>
>
> GL
>
> Jim, K4OJ
>
> ...hot off a day of this kind of stuff including rediscovering my
> six-pack still needs more than 12V to function properly....
>
>
>
>
>
> [email protected] wrote:
>
> > A friend of mine's 1000mp is having difficulties, and I am hoping
> > you can help me.
> >
> > 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: [email protected]
> > "Those who hear not the music. . . think the dancers mad."
> >
> >
> >
> >
> > Moderator: Ray Brown, KB�STN
> > _______________________________________________
> > Yaesu mailing list
> > [email protected]
> > http://mailman.qth.net/mailman/listinfo/yaesu
> >
>
>
>
> Moderator: Ray Brown, KB�STN
> _______________________________________________
> Yaesu mailing list
> [email protected]
> http://mailman.qth.net/mailman/listinfo/yaesu