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Author Topic: VHF and 70cm Yagi spacing suggestion  (Read 1602 times)
W6AOA
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Posts: 35




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« on: July 16, 2013, 07:16:25 PM »

I plan to mount a cushcraft 11 element (2 meter) and a K1FO 22 element (70cm) above my A3 Yagi.  My question is how far above the A3 boom AND how far apart side-by-side should the VHF & UHF yagis (Mounted vertically) be..

Tnx
Ed  W6AOA Pensacola, FL

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G4IJE
Member

Posts: 236




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« Reply #1 on: July 17, 2013, 10:18:45 AM »

The glib answer is to say "as far apart as possible", but in practice something like 6 feet above the HF beam and 6 feet apart would probably be OK.
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KO1D
Member

Posts: 383




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« Reply #2 on: July 18, 2013, 06:01:53 AM »

While not 100% answering the spacing with HF overtly the concepts should give you an idea.

STACKING DIS-SIMILAR YAGIS AND LOOP YAGIS
http://www.directivesystems.com/STACKING.htm

As a point of thought my 6m and 2 m antennas should be about 10-12 ft apart. The 432 should fall closer to the 6 than the 2. You can review this article and get some ideas on how to calculate for your needs.

Hope it helps.
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AA4HA
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Posts: 1377




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« Reply #3 on: July 18, 2013, 05:13:14 PM »

Vertically polarized antennas should be separated vertically. Horizontally polarized antennas should be separated horizontally.

For vertically polarized antennas they should be stacked with at least a few wavelengths of separation between antennas. Mounting them next to each other can cause you problems with excessive coupling and the elements of the antenna can act as parasitic elements on the other Yagi. That will mess up your gain and antenna pattern. Also you will have much higher levels of received signal from the other radio (even if they are not in the same band).

The same rule applies for horizontally polarized antennas but the separation is horizontal distances.

I have seen omni antennas (vert-pol) on skyscraper rooftops where they were separated by 20-30 feet but the received signal level on the other antenna was as high as +20 dB (tenth of a watt). You get up to signal levels like that and you are running the risk of damaging the front end of the receiver and you are definitely driving things into nonlinear operation and you will get intermodulation products.

I had the antenna mounting changed by elevating one antenna by 10' more and the signal level went from +20 dB to -15 dB (still very hot but maybe the front end will fare a little better).
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Ms. Tisha Hayes, AA4HA
Lookout Mountain, Alabama
W3HKK
Member

Posts: 593




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« Reply #4 on: July 22, 2013, 11:11:33 AM »

Ran a Cushcraft 11 element 2M  vertically polarized Boomer yagi  5 ft above my HF tribander or monobander....the KT-34XA  or HyGain 204BA.  Both worked just fine, with low swrs and fairly symmetrical radiation patterns.

Recent experience  with 6M,  2M and 70 cm yagi spacing (the club recently competed well in the ARRL VHF Contest) had  the 70 cm antenna ( 11 el.) five ft above  the 11 el 2M Boomer yagi , 5 ft above a 5 el M2 6M yagi - all horizontally polarized- on a 50 ft tower (plus mast). 
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