[VHFcontesting] Multiband VHF antennas

[Zack Widup]

Since I am primarily operating as a QRP Portable in VHF contests, I
need all the help I can get in the antenna department. It would be
nice to have a multi-band antenna that performs as well as a
single-band antenna, but does such a beast exist?

I am using a 6-element long-spaced Yagi on 2m (12 foot boom), similar
design on 222 with 8 elements (also a 12 foot boom) and a 12 element
on 432 (10 foot boom). The 432 antenna seems to perform the best so I
don't plan on changing it just yet. 144 seems to be my weakest band,
so I want to build an antenna with a longer boom (maybe 18 feet) for
this year's contests. Maybe I'll go to something longer on 222 also.

73, Zack W9SZ


On Mon, Mar 8, 2010 at 8:17 PM, Tom Carney <tomc at carneysugai.com> wrote:
> Earlier I had done some modeling of a 2M/432 single feedline antenna
> using the open sleeve technique.  These had not proven useful so I had
> abandon the approach.  Now, prodded by KK6MC's post, I tried again.
>
> This time I started with 4 element 2M OWA beam instead of a conventional
> design.  Right off, it looked promising.  The 2M OWA beam modeled at 8.8
> dbi (free space), flat SWR, on a 33 inch boom.  Just by adding a 432
> open sleeve "driver", I obtained over 7dbi with and SWR below .125 to 1
> on 432.
>
> I then started adding 432 elements.  With a 432 reflector and a single
> director, I obtained got up to over 9dbi with a slightly better SWR.
>
> Unfortunately, ever thing I tried to add more 432 elements, degraded the
> performance.
>
> Still, it's a simple antenna.  with four 2M elements, 3 three 432
> elements on a 33 inch boom I obtained almost 9dbi on both bands.  The
> pattern on 432 is more like a mushroom than what you would expect from a
> conventional yagi.  A very broad front lobe with only 8db front to back.
>  Not a world beater but looks promising for a Joe706 antenna.
>
> It's fairly critical on the spacing of the 432 driver but even a tenth
> of an inch mistake doesn't degrade things a lot.
>
> You should have a choke balun however.  Not sure the simple coin of coax
> will work at 432.  Might be a problem.
>
> I'll keep experimenting.
>
> 73,
>
> Tom K6EU
>
>
>
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