[1000mp] Tuner quirk

Mon, 31 Dec 2001 16:33:02 -0500

Put the TVI filter on the transmitter side of the tuner/SWR meter. Does the
presence of the TVI filter cause the transmitter to crowbar (reduce it's
output)? Keep the length of cable to the TVI filter SHORT, as in couple feet
or less.

If the TVI filter causes the transmitter to crowbar under these conditions,
you may have filter toast.

73, Guy.

----- Original Message -----
From: "Kok Chen" <[email protected]>
To: <[email protected]>
Sent: Monday, December 31, 2001 1:25 PM
Subject: Re: [1000mp] Tuner quirk

> Mark Tetrault <[email protected]> wrote:
> > My Mark V so far has been perfect. Yesterday I stuck a B&K TVI filter
> > in line. Now the tuner doesn't want to tune 160, 80/75, and 10 meters.
> > It tunes the other bands ok, but slower.
> >
> > I tried another filter, Bencher TVI, same results.
> >
> > I switched coax jumpers to the filter, same results.
> >
> > Pulled the filter and jumper back off line, tunes fine again!
> >
> > Does the MP/ MP Mark V not like TVI filters?
>
>
> Here is my weird conjecture.
>
> The rig itself puts out a small amount of harmonics (well, that
> is why we use a TVI filter in the first place :-).  Most TVI
> filters are not absorbtive (i.e., they do not dump the harmonics
> into a dummy load, like, say, a diplexer).
>
> The harmonics get reflected back to the rig.  It is not converted
> to heat (no frequency selective dummy load), and it is not converted
> to some other frequency (lack of non-linear elements in the TVI filter),
> and it does not go to the antenna port (or the filter isn't very good).
> Ergo, it is reflected.
>
> If the reflected harmonic components are larger than the reflected
> signal of the fundamental, the tuner no longer has decent phase
> relationship of error (reflected fundamental) vs reference (forward
> fundamental) signal to drive the tuning algorithms.
>
> I did say weird conjecture, didn't I? :-)
>
> 73
>
> Chen, AA6TY
>
> P.S., I remembered reading about the use of a diplexer (lowpass port
> to the antenna and highpass port into a dummy load) as an effective
> TVI filter.
>
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