2 Meter Repeater Antenna

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Andy Knepler:
I am in the process of setting up a 2 meter repeater.  I currently have an AEA ISO Pole type antenna that I was considering using at the repeater site.  My original reason for purchasing the antenna was because of the benifits of the "second skirt" design which helps to reduce the adverse effects of the tower in the radiation pattern.  However, the site where I plan to set the repeater up has a lot of RF activity.  I have heard that since the iso pole is a wide band antenna I may have problems with channel seperation.  The repeater has a 100 Watt continuous duty amplifier built in, so gain is not the most important factor.  I am really just looking for an antenna that will perform well on the receive end, and I would like to get the radiation pattern to be as omnidirectional as possible.  Any suggestions or advice would be greatly appreciated.  Thanks.

Steve Katz:
The AEA Isopole is a poor choice for a duplex operation, i.e., using the same antenna for transmitting and receiving, because it relies on aluminum clamped connections, and the "skirts" are barely connected (can actually be "not connected," depending upon the quality of the clamped connection) to the coaxial cable outer conductor which provides the RF current path from the duplex equipment to the antenna.  Repeater owners like myself (owned & operated VHF repeaters since 1973) have ruled out antennas having such construction as just impossible to work with.  This has nothing whatever to do with "performance," such as VSWR or radiation angle, or gain at horizon.  It has everything to do with duplex performance, that being the ability for a connected receiver to hear weak signals while the connected transmitter is also transmitting.  "Desense," or desensitization, is most often the byproduct of miniscule discontinuities in the antenna system; those could be in the antenna itself, or in the coaxial transmission line, or the duplexer, or any connection existing between these elements.  And I do mean "miniscule."  It is impossible to measure this influence with DC test & measurement equipment such as an Ohmmeter (although a Microohmmeter might show something)...we're talking about microohms of discontinuity, which produce microvolts of signal -- enough to desense or cause noise in a receiver, but not enough to damage anything else except repeater receiving performance.  As such, the best repeater/duplex antennas are constructed of extremely conductive, non-oxidizing materials which are soldered together to form permanent, extremely low-resistance bonds, and then permanently sealed against the effects of weather.  The Isopole meets none of these criteria.  A good all-around choice is the "Stationmaster" design originally produced by Communications Products Corporation, which later became Phelps-Dodge, and later still became Celwave Communications.  This antenna is constructed of soldered copper resonators, permanently and hermetically sealed in a fibreglas tube.  It's 20' tall overall (base to tip) and has a single brass tip exposed (which is at DC ground potential, and also hermetically sealed against the fibreglas tube) to help discharge static.  It is meant to mount on at least a 2.00" diameter pipe and very heavy-duty mounting clamps are part of the standard product.  Fed with solid-shielded coaxial cable such as "hardline" or Heliax, and using high-quality double-shielded connectors like Type N, this antenna will produce no measurable noise in a full-duplex system, even at high transmitter power levels.  That cannot be said of the Isopole, or of nearly any "amateur" antenna, especially those made of clamped aluminum pieces.  Good luck with the new repeater!

:
Can you give more information on your setup ?

Will you share the antenna for tran/recv or use
seperate antenna mounted at two places ?

Will you have to protect other repeaters
from your repeater emissions ?

We use folded diploles mounted away from
the west to protect a repeater from another
city 75 miles west of us (we do not use pl).

What equipment will you be using ?

good luck with the project.

73 luke

Jeff Lake:
I didn't read the replies completly but I WOULD NOT RECOMMEND AN ISOPOLE FOR A REPEATER. I'm the lead technican for our local radio club, We have dubbed the AEA isopole the big dummy load !!! We ran a side by side comparison for the old hams in our group, and had a Radio Shack 5/8 wave mag mount out perform the Isopole hands down !!!!
needless to say our repeater did not have the Isopole installed,
We opted for the RF-Products X-50HNA....NOT The Diamond Amateur Grade but the RF Commercial Grade...
For a little antenna that is barely 5 feet tall this thing TALKS big !!!!

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