[CQ-Contest] Re: [TowerTalk] 80m Dipole ssb/cw switching

[Mike]

Hi Dave,

I used a similar variation of the technique you describe at my station
in Ohio. Since I was partial to CW, I cut my 80 meter inverted-vee
for 3550 KHz, and then used a tuner match the antenna in the SSB
portion of the band. This allowed me to run "tuner free" on CW.

Just out of curiosity I modeled this configuration. As it turns out,
the additional loss penalty I was paying on SSB due to the feedline
mismatch was only about 0.8 dB (I was using around 100 feet of
RG-213 coax). This was born out in practice as then antenna
seemed to play fine on both modes.

73 de Mike, W4EF.......................

----- Original Message -----
From: "k8cc" <k8cc at mediaone.net>
To: "Mike Brown K9MI" <k9mi at home.com>; "Tim Duffy" <k3lr at k3lr.com>; "Jim
Breakall" <jkb1 at psu.edu>
Cc: <cq-contest at contesting.com>
Sent: Wednesday, November 14, 2001 2:30 PM
Subject: Re: [CQ-Contest] Re: [TowerTalk] 80m Dipole ssb/cw switching


>
> At 12:01 PM 11/14/01 -0500, Mike Brown K9MI wrote:
> >Another efficient method is feeding the 1/2 wave dipole with open wire
and
> >using a Johnson Matchbox. This gives maximum frequency flexibility.
> >
> > > 73,
> > > Tim K3LR
> >
> >I just went to this type of setup myself. The thing I need to check
> >and see how much bandwidth I get with it before needing to touch
> >it up. Of course, this would only come into play durring S&P. My
> >dipole ended up being 130ft overall due to our small city lot. Close
> >enough I would say though.
> >
> >73 - Mike K9MI
>
> For many years, I've used a coax-fed dipole cut for 3650 KHz, which I've
> matched to 1:1 on both CW and phone with a MN-2000 tuner.  This is very
> convenient, but recently I've come to wonder about the overall system
> bandwidth.  All of the K8CC amplifiers use glass bottle tubes such as
> 3-1000Z, 3-500Z, 4-1000A etc. (OK, my one 3CX1200 is not glass, but
> electrically its a 3-1000Z) which are not too cranky about load impedance
> changes.
>
> I recently ran some informal experiments with my setup.  I looked at the
> 2:1 SWR bandwidth at 3650 KHz (tuner out of line) vs. 3525 (tuner in line)
> and (3825 tuner in line).  I found that the bandwidth at 3825 was only
> slightly narrower than at 3650, while the bandwidth at 3525 was
> significantly narrower.
>
> A number of years ago, K7GCO tried to popularize the concept of the
"single
> knob tuner" for such applications.  Basically, you cut the 80M dipole
below
> the band, then insert a transmitting variable capacitor in series with the
> coax in the shack.  The capacitor is used to null out the capacitive
> reactance exhibited at the operating frequency - the higher you go in the
> band, the capacitance is reduced so the transmitter sees a pure
resistance.
>
> Its been my experience with shunt feed verticals on 160 that series
> elements (L or C) tend not to narrow the bandwidth of the system, however
> shunt elements will when they form part of a matching network.  The 80M
> dipole CW vs. SSB requires a single-element series solution such as Jim
> Breakall has described.  Using a full "tuner" when changes to the
resistive
> part are not required, will probably narrow the system SWR bandwidth.
>
> 73,
>
>
> Dave/K8CC
>
>
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