I'm in the process of building portable repeaters for use on the national interoperability channels. In UHF, that would include UTAC41-43. Those frequencies range from TX 453.4625-453.8625 and RX 458.4625-458.8625. I've assumed that I'll need three duplexers and will have to swap them out depending on which frequency pair I want to use. However, I came across this duplexer on ebay, tuned for the whole GMRS range, and it made me wonder if I could do the same in UHF with a similar portable duplexer. Any advice on whether this is an acceptable practice, or should I steer clear? Can you tune most of these portable duplexers to pass/reject this wide of a range ( 0.4mhz)? In your opinion would the downfalls of doing that (decreased functionality) outweigh the benefits? I'm just getting started in the world of duplexers--everything I've ever used was notched for a specific frequency pair, not a range. Any advice would be appreciated.
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Tuning a duplexer for a range of frequencies rather than just one pair
- Thread starter sbraun46b
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Project25_MASTR
Millennial Graying OBT Guy
It can be done but it's very dependent on the frequencies being used and the minimum separation between the lowest uplink frequency and highest downlink frequency. Using the same concept though, some 800 MHz duplexers are not field tunable because of the 45 MHz offset.
RFI-EMI-GUY
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You will almost certainly have worse rejection performance when you tune for 0.4 MHz . You can stagger tune the three reject notches (center plus near two edges.) within that 0.4 MHz, but it will result in worse rejection than when tuned on a single center frequency. I would sweep the duplexer as now tune for GMRS to see how well it performs and where the notches are placed.. If it is sufficient for your application, then tune for your new frequencies.
Flatpack duplexers have some inherent bandwidth and they should cover at least 100KHz of BW with some useable up to about 200KHz as you saw with the GMRS ad. The isolation will peak in the middle of the band and degrade at the edges and you have to tune and test them for bandwidth including testing the repeaters over wide range to make sure there is no desense.
If your repeaters are low power like 10w or less you might get away with just two duplexers to cover your needed 400KHz bandwidth.
If your repeaters are low power like 10w or less you might get away with just two duplexers to cover your needed 400KHz bandwidth.
12dbsinad
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DO NOT buy cheap Chinese flatpack ebay duplexers, they are total trash. Ask anyone with radio knowledge and they will tell you. If you insist on a mobile duplexer find a Celwave one. Personally I'd tune a duplexer for each frequency and when deploying them don't stick them on busy RF sites because it probably will puke and won't work worth a beans. A nice quiet site with not much around if you're only planning on using a mobile duplexer.
kayn1n32008
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You should have no issue getting a duplexer to pass 400KHz of band width. If you have the room, I would look at getting a Sinclair ResLoc BpBr duplexer and stay away from the mobile duplexer.
Thanks for the tip, as I'm starting to learn about duplexer.
We have 2 "tac" repeatersi n command posts that have all the UTACS in them and use a single Sinclair Duplexer. Tune in the middle and it works ok. For site repeaters I would do seperate for each but for most TAC stuff it works well enough. The channel we go to is the one we tuned for most of the time but has ability to move if needed.
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