I am curious about the effects of duplexers on repeater's efficiency. In a conversation between a couple of hams the other night, I heard one telling the other that duplexers reduce a repeater's transmit, and receive capabilities by 15 to 20 percent. While I would expect some loss in using them, is this a realistic quote?
Thanks for nay answers in advance.
duplexer "drain"
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It really depends on how well the duplexer is made and the quality of the connections to and from it. Commercial duplexers, Wacom, and Telewave to name a few, have high isolations and low losses that you just don't get with a celwave duplexer that fits in a GR300. You pay a big price for that performance. Also keep in mind that any system is only as good as its interconnects. Cheap cabling and amateur connector installs can turn the best hardware into a marginally performing system. So, the moral of the story and the answer to your question is that it depends. You can easily lose much of your receive sensitivity to a bad connector and cheap or damaged cabling. The same can be said for transmit power.
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Ray D. O'Mann #2
- Posts: 114
- Joined: Tue Sep 11, 2001 4:00 pm
Duplexers come in all shapes types and sizes, but generally they have low insertion loss. 15 to 20% is actually fairly bad, possibly as a result of either mis-tuning or attempting to tune an out-of-range frequency.
Duplexers use tuned cavities and critical-length intercabling to allow one frequency to pass, while rejecting the other. What usually happens with used equipment or amateur radio applications using commercial band equipment is that although the cavities and cabling can be retuned, the level of rejection might be lower, causing insertion loss and receiver desense.
The reason why is that the cables are critical length, cut for a specific frequency. The maximum allowable bandwidth of duplexers varies, changes in operating frequencies less than, say 2 to 5 MHz are usually ok, within the operating range. Sometimes even 10 or more MHz works. It really depends on the type of duplexer.
Anyways that's my $0.02 plus a buck and a half
Duplexers use tuned cavities and critical-length intercabling to allow one frequency to pass, while rejecting the other. What usually happens with used equipment or amateur radio applications using commercial band equipment is that although the cavities and cabling can be retuned, the level of rejection might be lower, causing insertion loss and receiver desense.
The reason why is that the cables are critical length, cut for a specific frequency. The maximum allowable bandwidth of duplexers varies, changes in operating frequencies less than, say 2 to 5 MHz are usually ok, within the operating range. Sometimes even 10 or more MHz works. It really depends on the type of duplexer.
Anyways that's my $0.02 plus a buck and a half
Last edited by Nand on Sun Jan 18, 2004 10:16 am, edited 1 time in total.
It's a fact of life (and physics) that a good duplexer will have an insertion loss of 1.2 to 1.8 dB. The best way to offset this loss is to use the lowest-loss feedline you can afford, and a good antenna that has at least 5 dBd of gain. My rule of thumb is to use feedline that does not exceed 1.0 dB of loss at the highest frequency. The antenna gain should be balanced against the pattern, because close-in coverage may suffer when very high gain antennas are used. One last comment: Factory tuning of duplexers is a good starting point, one that nearly always can be improved at the site if a service monitor is available.