Indeed "unaffected SWR" absolutely does not mean the pattern isn't
affected!! I tested an M2 4 el 40 (their 40M4LLDD) at 37' with a 6 element
15 at 12' (1/4 wave so high enough) ... with the booms at 90 degrees the 15
had normal FB (range tested) ... with them inline it was GONE! Completely
gone. HUGE impact and that was spaced 25' away. The SWR - changed - from say
a 1.1:1 at best to a 1.3:1 ... so obviously one could easily say "ah its
fine - the SWR essentially did not change" ... WRONG.
If you do the model generally a 40 and a 20 will have some impact - the FB
will always be the first to go - and in this case it might mean a
degradation of 5 db or so .... gain is the least impacted with essentially
no to maybe 1/2 db change - SWR is next in line but as noted above it ISN'T
a good test variable.
The X40N's had their linear loading spaced at a distance such that it
divorced the sections on 15 meters. Testing shows that it pushes the
resonance close to if not in to 17M .... likewise when I designed a stub to
be used on the 40M4LLDD which worked to move it away from 15 - but pushed it
to 17M. Optibeam's OB4-40, which I have (sold the M2) has both proper
distance to the loading element (in their case a coil) as well as a stub. It
shows no impact on 15 or at least small enough that I've not been able to
measure a degradation on the FB on 15.
I'd say you'd have a 100% chance SOMETHING is going to be impacted on a 5
band hex beam. The amount will vary.... for most they happily move along
knowing they have the antennas...
Gary
K9RX
-----Original Message-----
From: Guy Olinger
Sent: Monday, May 1, 2017 12:29 PM
To: Mpridesti ; towertalk@contesting.com
Subject: Re: [TowerTalk] Interaction potential Hex and 40 m dipole
On Mon, May 1, 2017 at 6:48 AM Mpridesti via TowerTalk <
towertalk@contesting.com> wrote:
Any experience here placing a shortened 40 M dipole near and below the Hex
beam?
Force12 famously kept their x40N series of 40m near full size yagis from
interfering with their XR19, XR31, etc series of 20/15/10 tribanders by
tinkering with the 40m folded element design until the secondary resonances
lay in the WARC bands. That allowed mounting them within six feet on the
same mast in the same direction without discernible effect on the
tribander's pattern.
Without experimentation on the 40m antenna, there is no way to know what
bands may be bothered on the hex beam. Further, unless someone has the
exact same setup as you there is no basis for extrapolating their results
to your situation, particularly since feedline length and whether
non-active coax are grounded or open at the coax switch will also affect
results.
Also note that "unaffected" SWR does not mean the pattern has not been
trashed.
Placing 80 and 40 dipoles/vees 30 feet away is the only way to minimize
interaction with a five band hex beam for sure.
I'm sure that wasn't what you wanted to hear.
73, Guy K2AV
--
Sent via Gmail Mobile on my iPhone
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