I would like to reposition my 2M/70cm Vertical (Diamond X50) to a higher
position.
One option is to mount it above the TV aerial, I understand that the signal
radiation below the antenna is very small, does anyone have any experience
of a similar setup?
If so what kind of distances would you suggest between the antennae?
Obviously my main concern is TVI and poorer performance from the Diamond due
to its close proximity to the TV aerial.
hey there. My sugesstion is the higher you can mount the vertical above
the tv antenna the better. Persinally I would mount the antenna a min.
of 3-5 feet above the TV antenna. Just rember that the higher the
antenna the more loss in the coax.
Adding some form of choke balun, or some ferrite beads clamped onto
the outside of the coax, immediately below the antenna, might also be
a good idea. This will reduce the amount of RF which comes back down
the feedline and which might be coupled into the TV antenna.
I would also strongly suggest that if
you do mount the vertical above the TV antenna that you invest in some
TVI filters. I think radio shack or you local electronics part store
should have some in stock. ( They sould be fairly cheap. $3-$5 each or
something like that)
Standard TVI filters will probably not help matters much. The usual
television TVI filter is a high-pass filter, which will do an
effective job of keeping HF ( 30 MHz) out of the TV system and which
will probably have some effect on 6-meter signals as well. It will be
quite ineffective at keeping 2-meter signals out of the TV, since
these fall right in between the TV-VHF-low and TV-VHF-high bands and
are on the high-pass side of the filter's knee.
There are specialized band-stop which can be installed to "notch out"
the 2-meter signals. They're harder to find than ordinary low-pass
and high-pass filters. You may be able to find a cable-TV notch
filter which will do the job - if you can find one which is designed
to take out cable channels 17-19, that could help matters.
I had severe TVI problems at home due to 2-meter signals getting into
the TV antenna. The problems were noticeable on the TV in the den
(fed directly from the antenna via a splitter), and were very bad on
the several TVs and VCRs in the living room (fed via a cheap Radio
Shack distribution amplifier, which was no doubt being overloaded into
severe clipping and distortion due to the high RF levels).
The solution I ended up with is a CA7X-144/148 bandstop filter from
http://www.tinlee.com - it has a bandstop notch of better than 35 dB
between 144 and 148 MHz. Not cheap, but it seems well-built and has
cured the TVI problem when I key up one of my 2-meter rigs.
--
Dave Platt AE6EO
Hosting the Jade Warrior home page:
http://www.radagast.org/jade-warrior
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