[50mhz] Stack spacing question

[Roger, K4RW]

Mark,

I have a vhf tower that has almost an identical antenna arrangement as you
are describing for your proposed setup.  The tower is 41' with a hazer
mounted tram. The mast is 15' total with about 11' above the tower top. The
6m antenna is a modified Cushcraft A50-5 (W5WVO designed mod - 17' boom).
This antenna is about 10" above the tower top. The 2m antenna is a Cushcraft
4218xl Boomer (unmodified) with a 28' boom.  The 2m antenna is mounted at
the top of the mast.  The antenn booms are about 9' apart. A picture of
these antennas can be seen if you look up my call on DXWATCH (larger
picture) or QRZ.

These antennas have performed very well for a number of years.  I have
noticed no interaction or degradation of the antenna patterns due to this
stacking arrangement.

Here is a link to a good explanation of various aspects of antenna stacking
that you might find informative.
http://www.ifwtech.co.uk/g3sek/stacking/stacking2.htm 

The best course is to actually model the proposed stack with one of the
modeling software packages and see what the patterns look like.  The antenna
modeling software that I use quite often is MMANA.  MMANA is a free download
and is quite good.

Roger, K4RW


-----Original Message-----
From: 50mhz-bounces at mailman.qth.net [mailto:50mhz-bounces at mailman.qth.net]
On Behalf Of Mark Drieci
Sent: Saturday, August 20, 2011 4:43 AM
To: 50mhz at mailman.qth.net
Subject: [50mhz] Stack spacing question

I am erecting a new VHF tower with a modified Cushcraft A505 (18 foot boom)
and a Cushcraft 17B2 (31 foot boom) in a vertical stack.

Conventional wisdom suggests that the 6M antenna be placed atop the 2M
antenna as it has the shorter boom.

 

I have read the section of the ARRL Antenna book where it describes stacking
scenarios of the 2M over 6M beams, but there are none described that are
similar to my own.

I am seeking input from the list members on the optimal stacking distance
between the two yagis to minimize interaction

 

Any comments on this subject are greatly appreciated.

 

Thank you in advance.

 

Mark - KA4MAY

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