Hi, Ignacy,
I didn't see any response to your proposal.
There are several issues.
1) If the two antennas are using the same elevated radials, the radials
cannot possibly be effective on both bands without special engineering or
switching. Well-engineered ground radials do not have resonance effects and
would work for your purpose. Elevated radials have an insulated end up in
the air, and without additional work will be resonant at the fundamental
(3.5 MHz) and three times the fundamental (10.5)
Whatever you are using to tune the radials down to 160 must be switched out
to operate on 80m. You may have done that, but if not, then you are most
likely using the shield of the feed coax, possibly with a ground rod in
parallel, as the counterpoise on 80 meters. This is usually remarkably and
non-intuitively very lossy. Most baluns or common mode current blocks,
unless specifically designed for low-band blocking, DO NOT have enough
blocking to keep 80 off the feedline coax and the ground rod in such a
case. The balun itself can further add to the loss in these instances.
2) The two aerial wires are close coupled, just as effectively as if they
were two wires wound on the same transformer core. On 160 the 80 wire is
too short and does not bother 160. Operating on 80 the 160 wire by itself
is RESONANT (a half wave). The 80 wire CANNOT function as a normal vertical.
If the 160 wire is grounded by the antenna switch, then you have coupled a
ground rod into the mix by the transformer effect between the two wires.
If the 160 wire is left open, then there is full 80 m RF current on the 160
wire, and the pair has an odd pattern. If the 160 wire is left coupled to a
piece of coax which is simply not selected in the shack, then you have an
undetermined outcome which just depends. It seems a law of RF nature that
undetermined outcomes are unsatisfactory until proven otherwise.
The FCP project has a beta extension going that directly uses the 160 L
over FCP on 80 meters, as an endfed 80m halfwave L. This method was used
single band assisted high power on 80 meters in the CQWWDX CW from North
Carolina and resulted in 276 QSO's 18 zones, and 80 countries in 14 hours
of operating time. That score is currently #2 North America, #1 in 4th call
area in CQ's listing of claimed scores for 80SOSBHP(A), and if the log
holds up, will get a certificate.
So there is a way to do that well. But two separate wires on the same
radial field without some carefully engineered serious switching of
components, from this author anyway, is fairly well guaranteed to get
exactly the results you report.
So far we have 3 hams using the 160 L over FCP on 80, all with good
results. So there is a good method coming.
73, Guy K2AV
On Mon, Dec 5, 2016 at 2:48 PM, Ignacy Misztal <no9e@arrl.net> wrote:
> I have an 80m full-size wire vertical and 160m inv L using the same 8 long
> elevated (and tuned) radials, each 20m long and 2m high. The RCS-4 switch
> picks up either antenna. Having separate feeds makes tuning simple.
>
> Compared to an 80m flattop at 20m fed with ladderline, the 80m vertical is
> usually 10 db down, DX included. The vertical is still better where the
> flattop has a null.
> Recently I put an endfed for 80-10m in an inv V configuration in a
> direction where the flattop has a null. After comparisons, the vertical is
> going down. The endfed is easy to set up, takes a KW easily and is
> multiband, if need be.
>
> My results may be due to poor Georgia soil.
>
> It is good to have many antennas and make A/B comparisons.
>
> Ignacy, NO9E
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