My rover is probably the most extreme situation I have observed... The 6
meter and two meter station use preamps, the 6 meter station dumps out
around 360W, the two meter station, 160. The antennas are around a foot
apart, and the two meter station is not quite a quarter wavelength over
the roof of the vehicle when used mobile, with the 6 meter antenna above.
That close to the roof, there is some additional reflected power when
transmitting, but not much, and some antenna gain reduction. When elevated
to the stationary operation height, these problems go away.
I do use a single bandpass cavity on each band to keep the power from one
band from messing up the other. Works great as long as the relay contacts
in the amplifiers are clean! The other benefit is the reduction in
background noise "in-band" form out-of-band sources.
I jokingly refer to these as RF roofing filters! Especially the 6 meter
can, as it is bolted horizontally to the ceiling of the rover vehicle
interior... Only place I had room for it! The two meter bandpass cavity
being only 2 feet high, vice 5 feet,
sits on the operating desk of the two meter station.
My 222 station uses the "full-band" DCI filter, mainly to keep the local
channel 13 broadcaster from rendering that band unusable locally, but does
prevent interstation interference. Since this band and 432 share an FT
726R
they do not get operated simultaneously. These antennas are mounted at
the same height as the 6 meter antenna above the roof when the rover is
moving, but, due their shorter wavelength, they work just fine where they
are mounted. They can be elevated another 2 feet to allow separate
rotation of these bands from the 903+ stack when parked, as the vertical
pipes holding the 222/432 antennas will strike the box containing the
5.7/10 gig station
if this step is not taken. Otherwise, in the "road mode" nested position,
the whole 222/432 plus 903+ can be rotated together when parked.
Harmonics from the bottom two bands do get passed through the cans, although
attenuated somewhat. I have noticed some degredation in S/N ratio on weak
signals on 222 and 432 from the 2 meter station on occasion, but I noticed
these occasions seem to coincide with these antennas being pointed into
each other! But, noise sources found in common retail center parking lots
can be
much noisier!
Look me up on QRZ.com for a picture...
Eric
KB7DQH
> Hi Les --
>
> Here's a great page of information on that very subject. It turns out that
> you can place them closer than most people think.
>
> http://www.directivesystems.com/STACKING.htm
>
> I've stacked them really close for roving, and had some 6m vs 2m issues. I
> tried quarter-wave coax traps with some success. The best solution was two
> separate masts for 6 and 2. At 100w, the problem went away.
>
> 73 de Joe W3BC
>
>> Some local VHF'ers have raised a concern about the proximity of my
>> various V/U antennas...
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