Monday, November 1, 2010

Kenwood TKR-850 as a D-Star Repeater

In my opinion this type of thing needs more attention. After all do-it-yourself has long been a hefty part of this hobby. And there is no better way to learn than a hands-on project like this.

Reason number two would be economics, but I think that is obvious.

The third is spectral savings. D-Star is narrowband, but buying a new system just robs another frequency pair from the pool. It seems people rarely take repeaters off the air, even if nobody really uses them. And these days it seems there are more repeaters in a geographic area, than there is activity.

So it seems best in my mind to convert something already out there. This would make a great club project.

This is great example of continued innovation of D-STAR technologies by incorporating non-Icom products into D-STAR environment.

Date: Thu, 07 Oct 2010 05:32:17 -0000
Subject: K8BIG Port B Using Kenwood TKR-850 Interfaced to ID-RP2C

The K8BIG Port B D-Star Repeater in Cincinnati, Ohio is successfully running using a Kenwood TKR-850 Interfaced to the Icom ID-RP2C in place of the Icom Band module (ID-RP4000V). The usable range of the repeater has been effectively doubled from around 25 miles radius to 50-55 Miles radius.

The K8BIG system is on the WCPO-TV Tower overlooking downtown Cincinnati, OH with the antenna at 700' AGL. There are 3 50,000 Watt FM Radio transmitters, 1 250,000 Watt VHF DTV Transmitter, and 2 3,000 Watt LPTV stations on the same tower along with various commercial VHF/UHF/220 transmitters so the RF environment is pretty harsh - add in the neighboring (2 Blocks) tower with a similar complement of transmitters and it is downright brutal for any radio equipment.

The Icom band module was being swamped by the high RF levels at and surrounding the site, causing very poor effective receive sensitivity even after the TX-RX BpBr Cans and an additional band-pass cavity. I had partially remedied this with one side of a reject-only mobile duplexer, but that introduced around 6 dB of insertion loss. Even with the 6 dB insertion loss the effective sensitivity was improved. The Kenwood repeater has a much tighter front end and much better selectivity with adjustable front-end helicals so the additional receive filter is not necessary and the 6 dB insertion loss was removed.

After the interface was built we were able to plug and play into the Icom ID-RP2C controller and gateway. With the exception of the increased range there is no operational difference in the repeater - everything works identically to the Icom band module. Commands work, data works, D-Rats works, etc.

I will be building more of the interfaces shortly which can be used to interface any 9600 baud-capable analog repeater directly to the ID-RP2C. Anyone interested please let me know.


Dan Woodie

You may want to look at;
Michael, VK5ZEA's Homebrew DV Node Adapter to ID-RP2C interface.

John, K7VE's Kenwood TKR-820 Node adapter retrofitting.

And/or my Motorola GM300 retrofitting and commentary.

As a technical side note, one thing to consider when converting analog repeaters is the receiver IF bandwidth. To date there has been little discussion on narrowing receivers bandwidth to match the narrower D-Star signal. Just be aware that converting a 1950's era repeater to D-Star that might have a 60 Khz I.F. would be vulnerable to adjacent channel interference. A good overview of the theory can be found in a reprinted article from Ham Radio Magazine 1985, by WD5IBS.

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