I have an old Ten-Tec 4229 tuner that is on its second ceramic wafer switch
(this is
the switch used to change the L-network configuration from Hi-Z step down to
Lo-Z
step up). I destroyed the original switch using an SB-220 and a center-fed zepp
that
must have had a particulary high input impedance. The SB-220 suffered no damage,
so it is my belief that the damage was caused by arcing of the switch contacts
that
resulted from the excessive RF voltage associated with the Hi-Z of the antenna.
That is not to say that parasitics aren't in the realm of possibilities. Based
upon my
limited experience, I don't know enough about the impedance characteristics of
HF tank components in the VHF range to really say with any certainty. What is
clear
to me, is that load mismatches (wrong antenna, improper tuning, etc) can
generate
RF voltages at the operating frequency which are well in excess of nominal
operating
levels. This seems to me to be a more likely explanation for switch failure.
73 de Mike, W4EF..............
----- Original Message -----
From: "measures" <2@vc.net>
To: <Wt8r@aol.com>; "Tom Rauch" <W8JI@contesting.com>; "AMPS"
<Amps@contesting.com>
Sent: Monday, January 01, 2001 9:14 AM
Subject: Re: [AMPS] Alpha
>
> >
> >In a message dated 12/29/00 12:37:26 PM Eastern Standard Time,
> >w8ji@contesting.com writes:
> >
> >> Hi Bob,
> >>
> >> > I don't intend to start a war, however based on my observations over the
> >> > last 2 decades (at least) in going to rallies (what Americans call
> >> > hamfests) and my observations of some of the questions which crop up on
> >> > the ham radio newsgroups the average ham is too lazy to do anything.
> >>
> >> I don't intend to start a fight, but from my viewpoint the average
> >> ham is too quick to condemn everyone else.
> >>
> >> > Some of the comments which appear on Rich Measures web site about
> >> > commercial equipment are well justified, rigs with so called fast break
> >in
> >> > using standard power relays to switch linears, no soft start for power
> >> > supplies, short circuiting HT lines as a safety measure, band switches
> >> > that arc because there is inherent in the design of an amplifier a cause
> >> > for VHF parasitic.
> >>
> >> I hate to tell you this, but if you think a VHF parasitic can arc a
> >> bandswitch you need a course in electronics 101.
> >>
> >> Perhaps you should look at the voltages and currents required to
> >> do that, instead of being critical of other for not knowing what is
> >> going on.
> >>
> >> Obviously you haven't researched the problem.
> >>
> >> 73, Tom W8JI
> >> w8ji@contesting.com
> >> ========================================================
> >
> >Tom,
> >
> >Since you are not the average ham, what, in your humble opinion, is the
> >cause of bandswitch arcing ????????
> >
> >You seem to have eliminated all the things that DON'T cause arcs, what is
> >the real cause?
> >
> ? according to Mr. Rauch, he has not completed Electronics 101.
> >
> cheers, Dave.
>
> - Rich..., 805.386.3734, www.vcnet.com/measures.
> end
>
>
> --
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>
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