At 08:20 PM 2/26/96 -0500, JBaumgarte@aol.com wrote:
>John,
>I very much enjoyed (and appreciated) your comments on this issue. Let me
>add another little hooker!
John -- tho this wasn't addressed to me, I couldn't resist commenting. See
below.
>I have two C3 in a phased stack--both rotatable
>individually--at 53 and 110'. Because of guys, 53 is absolutely as high as
>it can be. Being in northern MN and very interested in domestic contests,
>spraying is important, however, I have been finding in checking with DX
>stations that there are apparantly some pretty big gaps in my coverage
>(angular) when phased in the same direction.
Just for fun, I modeled your stack in EZNEC. With the usual caveats about
models not necessarily reflecting reality, I see what you mean. On 20m. the
stack gain is OK - 14.67 dBi, but the F-B ratio is badly degraded by a big
low-angle lobe off the back - only about 6 db. On 15, the F-B is better,
but there is a big hole off the front (roughly 10.5 to 44 degrees elevation
at 3db down, and there is a lot of radiation sprayed at high angles between
45 and 90 degrees (straight up). The pattern has a similar hole on 10 as well.
the I guess, like most of us, I
>would like to keep on improving things! The potential of putting a fixed 3rd
>C3 in the middle aimed at EU is an option.
This looks pretty good, when all 3 are pointed to Europe. On 20, the main
lobe is 16.06 dBi, and the F-B is 15 dB. On 15, the stacking gain is very
good - 17.45 dBi, F-B is decent at abt 12.5 dB, and there's no high-angle
radiation to speak of.
> Now, the question! What happens
>when the rotable antennas are both aimed at JA with top & bottom in phase and
>the 3rd antenna is not connected, but of course is a resonant presence in
>between? (fixed 90 degrees off of the phased pair)
I ran this case too. It's funny-looking! With the 81-foot antenna turned
90 degrees from the other two, the stack gain on 20 for the remaining 2
drops to 12.46 dBi, the F-B is degraded to about 6 dB, and there's a big
slug of high-angle, resulting from some vertical radiation that is not
present when the three antennas are aligned together. The azimuth pattern
is indescribable! On 15, the stack gain is down to 13.28 dBi, and again
there is substantial vertical radiation.
>
>Your comments on this and many other antenna issues are mightily appreciated
>(both here and at Dayton!)
>
>73 John, K0IJL
>
If you'd like, I'd be glad to fax the patterns to you, (either)John. Just
give me a number. I've been contemplating a 2-high C-3 stack, which is why
you caught my interest. My preliminary fiddling suggests that a good
compromise spacing for 20 and 15 with the C-3 is pretty small, on the order
of 27-30 feet, significantly smaller than for monobanders or longer-boom
tribanders. Couldn't you place the lower C-3 above your middle set of guys?
73,
Pete Smith N4ZR (n4zr@ix.netcom.com)
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