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Old 08-02-2012, 11:54 AM
K0MTB K0MTB is offline
Join Date: Jul 2012
Location: Colorado
Posts: 4

Kevtheskin and kayn1n32008,

Thanks for the replies and ideas, gents!

I’ve tried to get my repeater working with several antenna and duplexer configurations. Kayn1n asked about this. I’ve tried it with…

+ Two HTs and their respective, on-board, rubber-ducky antennas (spaced as far apart as the Radio Tone interface cables would allow—about 6’)
+ Two HTs connected to mag-mount, dual-band antennas (one on a bar-b-que grill, another on a 2’-square piece of 18_ga steel sheeting), placed as far apart as the mag-mounts would allow (~30’ horizontally—this might have been my problem…see below).
+ Two HTs connected to a cheap mobile duplexer that was then connected to a “Ventenna” dual-band antenna on the top of my house. (I also tried the duplexer connected to the mag-mount antenna on the bar-b-que.)

The duplexer was tuned by Joe Chung at RadioTone as follows: HIGH 467.7000_MHz and LOW 462.7000_MHz.

While researching my issue I came across another post by WA0CBW located at, who stated:

“According to calculations for a 5 watt transmitter to a unity gain antenna you would need 65 db of isolation between the TX and RX antennas. That equates to 26 feet of vertical or 481 feet of horizontal separation.”

In my rubber-ducky and mag-mount antenna configurations I was never anywhere near 481’ of horizontal separation! So good chance the proximity of the antennas, as kayn1n explained, is my problem. I should be able to test this by using a mag-mount antenna on the ground for one “side” of the repeater, and the Ventenna (on top of a near-three-story house—real close to at least 26 vertical feet) for the other “side” of the repeater. That should give me the isolation I need.

But what bugs me is that I DO have a duplexer, and I have used it with the Ventenna, and I still had desense issues. I wonder if my duplexer is not working correctly…or is improperly tuned…or I have crumby cabling between the radios and the duplexer. I’m using the same exact cables (and probably the same duplexer!) kpoe_28 is using in his portable repeater, as seen here, and his set up appears to be working fine.

I have an amateur radio friend coming over to do some work on his mountain bike in the morning. We’re going to do some more troubleshooting and I’ll try to implement some of the ideas kayn1n has suggested and see what we come up with. For the greater good I’ll be sure to post the results—maybe this will be of benefit to others in the future.

Thanks again for the help, guys. I appreciate it!

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