[NLRS] 6 and 2 meter antennas

[Dr. Gerald N. Johnson]

On 1/25/2012 10:01 AM, Marciniak, Ed wrote:
>
>
> Is it possible that you might win in a tradeoff of height for gain by
> putting some (relatively) small antennae higher up?
>
In 60s vintage ARRL VHF Handbooks there was a graph of height gain. I
suspect it was based on greater distance to the optical horizon and so
the higher the antenna the further the optical horizon and so the
stronger the signal beyond the horizon. I've not see that chart lately.
I do know that the 432 stations in the cities with low antennas don't
hear me and I don't hear them at 200 miles. Yet the other stations I
have no trouble working.

> Let's say 13db gain at 50 ft vs 16db gain at 30 feet including the
> difference is coax loss?

The lower gain antenna at the higher elevation probably has the better
signal at a distance, providing the coax is RG-213 or fatter. Coax cable
costs or gains a lot at any elevation. More at 432.
>
> If you move the antennae spacing to 1 wl at higher band, how much
> cross coupling is there between bands? Is protecting preamps a
> concern?
>
I didn't look at power in the other band driven elements. I'm sure there
is some and it depends on the relative distances between driven
elements. I found some small variations in gain and pattern moving the
close spaced yagi fore or aft. Probably there is an element combination
and spacing that would allow closer spacing if the high band elements
just happened to fit between the low band elements. But the same design
432 yagi has three times the element density as the low band yagi. In a
multi op station with yagis even wide spaced,it would be prudent to
protect the preamps with high pass and low pass filters or band pass
filters because many a preamp is only 1 or 2 dB down at 1/3 or 3 times
the rated frequency. And FETs tend to not survive a couple volts RF on
the gate.

> One year Ron and I went to the four corners by Mankato for a contest
> and ran 432 and 1296 simultaneously using 24 elements on each spaced
> maybe 18 inches apart on boom. It worked well, and his 3rd harmonic
> didn't cause me any desense.
>
>
73, Jerry, K0CQ