> I'm thinking of putting up a 10 meter vertical to use with the 2nd radio
in
> the 10 meter contest, using one radio on phone and one on CW. I'm hoping
the
> vertical will result in less interference between the 2 radios than
putting
> up a low tribander. I have a 4 element yagi stack at 53' & 36' for 10
> meters currently.
This is a real problem!
Remember a horizontal antenna radiates with "vertical polarity" off the
ends (even in the far field), and the view of the antennas is complicated
by the fact they are in the near field zones. In the near field zone,
polarity means almost nothing! It's tough to get any sort of "null" more
than a few dB with large elements.
You'll have a lot more coupling than you ever expect, you can bet on that!
> Stubs and bandpass filters won't work with 2 radios on the
> same band. Being on a city lot there is not alot of room for seperation,
> maybe 50' maximum. The vertical would be mounted at about 10' elevation
on
> my garage. I've got a base for an HF2V that has about 34 radials for 80
> meters. I was thinking of using this base, and unrolling the radials
about
> 8' each, leaving the rest rolled up.
I wouldn't do that, I'd just roll em on out. The more you spread out the
radials, the less loss the system will have.
> Preliminary research shows 5/8 wave would give better low angle radiation
> and gain. Any thoughts on whether 5/8 wave would be better or worse for
> interference vs 1/2 wave? Any other thoughts about this?
I doubt you'd find much difference. A 5/8 wl antenna, contrary to rumor,
forms its pattern many wavelengths from the radiator. It is the ground
several wavelengths around the antenna that forms the "image" that makes
the 5/8 wl (and 1/2 wl) vertical antenna have gain and pattern compression.
Not only that, the 5/8 wl vertical antenna has gain because its CENTER
height is 5/16 wl above earth (or a VERY large groundplane). Move the
center up in the air, without moving a nearly-perfect very-large (over two
or three wavelengths in radius) perfectly-flat groundplane to the same
height and you can find the 5/8 wl antenna has a net LOSS over a 1/4 wl or
1/2 wl groundplane!
That's why 5/8 wl and 1/4 wl antennas, in test range measurements, perform
about the same. All that 3 dB gain stuff is bull.
I'd try the antenna Steve, it might work... but in a situation like this
luck has more to do with results than skill or planning. Use a 1/4 wl or
1/2 wl antenna, stay away from a 5/8 wl antenna unless you live on a large
flat copper sheet and ground mount the antenna.
73 Tom
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