Introduction to Repeater Building

10/9/2018

George KJ6VU walks us through the most common components found in a modern FM repeater. We cover antennas, duplexers, coax, radios, controllers, and other helpful information for those who are considering taking on the project of an analog repeater build.

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Case for 12V DC Power Strip from Rocket City 3d - https://rocketcity3d.ecwid.com/Ham-Radio-Workbench-12V-DC-Power-Strip-Case-p114464423

OpenSpot 2 - https://www.sharkrf.com/products/openspot2/

POCSAG - https://en.wikipedia.org/wiki/POCSAG

Google Assistant enabled Repeater - https://www.youtube.com/watch?v=m52-3EuQfnk

Benchduino - https://groups.io/g/benchduino

KJ6VU’s Previous Repeater Episode - http://hamradio360.com/index.php/2014/10/08/10/

Repeater Builder - http://www.repeater-builder.com/rbtip/index.html

CDM Repeaters - http://www.repeater-builder.com/motorola/cdm/cdm-index.html

MaxTrac Repeaters - http://www.repeater-builder.com/motorola/maxtrac/maxtrac-index.html

Sierra Radio Systems Repeater Controllers - http://www.sierraradio.net/

Hustler G6 440 - https://www.dxengineering.com/parts/hsr-g6-440

PAVE PAWS Over the Horizon Radar - https://en.wikipedia.org/wiki/PAVE_PAWS

Coax Feedline Loss Calculator - http://www.timesmicrowave.com/calculator/

Remote Site Monitoring Episode - https://www.hamradioworkbench.com/podcast/remote-repeater-site-monitoring

QST Voter Article - http://www.ldgelectronics.com/assets/discontinued_manuals/RVS-8.pdf

1 Comment

Clint - KA7OEI link

11/26/2018 13:55:11

Great podcasts - thanks for doing them!

At about 70 minutes into the podcast (1:10) you mention band-pass/band-reject duplexers (Bp/Br) - but didn't bring up an important fact: The vast majority of the so-called "band-pass/band-reject" duplexers really *don't* offer a true, wideband "pass" response. The "band-pass" part seems only to apply to within a few MHz of the design frequencies and it falls apart further away.

None of the typical Bp/Br duplexers that I have ever seen - regardless of brand - will offer the off-frequency rejection of a humble band-pass (only) filter and will typically offer only 5-20dB of rejection of signals a few MHz to hundreds of MHz away: This is easily demonstrated if one "sweeps" them over a wide frequency range. This is a particular problem shared sites where other signals are 10s to 100s of MHz away and those signals will simply pass through: Any isolator on a transmitter will have little effect of off-frequency signals. (I have seen non-standard duplexers that have included pass cavities, but these are quite rare.)

An example was a D-Star stack that was installed on a local mountain top: With just the 3-can duplexer, the receiver experienced 40+dB desense (there was 100mW of RF at the RX terminals, through the duplexer) and it took two pass cavities in series to make the Icom repeater's receiver (a couple of mobile rigs in a box) happy.

It is for this reason that at all of our club's repeater sites that there is at least one band-pass (only) cavity on each of the TX and RX legs: Not only does it keep out the off-frequency signals, but it is also an excellent component in lightning protection.

If interested, see this articles at one of our local club's site explaining the issue when the D-Star stack was installed: http://utahvhfs.org/dstar_repeater_installation.html

73

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Introduction to Repeater Building

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