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Intermod duplexer... Are these specs considered good or bad?

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smokey222

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Good Morning on this Memorial Day. Came across a duplexer brand called "Intermod" model Model: D440N-4, made in Canada, for what seems to be a great price (about 268.00 USD). I am seeking input from someone knowledgeable about what is considered decent parameters as I just don't know. Below is what is listed...

Electrical Specifications Frequency Range MHz 406 to 470 Return Loss(min) dB 18 Insertion Loss(nominal) dB 0.6 Isolation(nominal) dB 80 Impedance Ω 50 Tx-Rx Separation (*) MHz 5 Average Power Input (max) W 100


Thanks in advance,
Scott
 

prcguy

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It sounds like a notch only mobile duplexer. It should be fine for a low power repeater in a low RF environment like your house. It would not be suitable for a commercial repeater site.

Good Morning on this Memorial Day. Came across a duplexer brand called "Intermod" model Model: D440N-4, made in Canada, for what seems to be a great price (about 268.00 USD). I am seeking input from someone knowledgeable about what is considered decent parameters as I just don't know. Below is what is listed...

Electrical Specifications Frequency Range MHz 406 to 470 Return Loss(min) dB 18 Insertion Loss(nominal) dB 0.6 Isolation(nominal) dB 80 Impedance Ω 50 Tx-Rx Separation (*) MHz 5 Average Power Input (max) W 100


Thanks in advance,
Scott
 

smokey222

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It sounds like a notch only mobile duplexer. It should be fine for a low power repeater in a low RF environment like your house. It would not be suitable for a commercial repeater site.
I should have provided more detail... I am trying to put together a decent gmrs repeater using a DB404 antenna, up to the permissible 50 watts output. I have LMR400 line that I was planning on using. Thanks you for your reply, also any comments on this type of setup?
 

prcguy

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I've had ok success up to about 25w on a notch type mobile duplexer. It depends a lot on the repeater. If its a GE Master series or Quantar or other high end repeater you can usually get by with a minimal duplexer because the transmitters are so clean and the receivers have good tunable front ends. If the repeater is a couple of wide band mobile radios or cheap off brand repeater, then you will probably have a lot of trouble.

You never want to use LMR cable anywhere in a repeater system, only good quality coax with copper or silver plated braid or Heliax, no foil shield with braid anywhere. No nickel plated connectors either.

There are tests you can do once the repeater system is installed by using a directional coupler in the antenna line to generate a weak signal into the repeater. You turn the transmitter off and test the SINAD level. Then do the same with the transmitter on as the repeater would normally operate. If there is no change in SINAD then your good. With the components you are considering expect some degradation when the transmitter comes on, which will cover up weak signals and limit the usable range.

And if its a low level repeater get a bigger antenna.

I should have provided more detail... I am trying to put together a decent gmrs repeater using a DB404 antenna, up to the permissible 50 watts output. I have LMR400 line that I was planning on using. Thanks you for your reply, also any comments on this type of setup?
 

smokey222

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I've had ok success up to about 25w on a notch type mobile duplexer. It depends a lot on the repeater. If its a GE Master series or Quantar or other high end repeater you can usually get by with a minimal duplexer because the transmitters are so clean and the receivers have good tunable front ends. If the repeater is a couple of wide band mobile radios or cheap off brand repeater, then you will probably have a lot of trouble.

You never want to use LMR cable anywhere in a repeater system, only good quality coax with copper or silver plated braid or Heliax, no foil shield with braid anywhere. No nickel plated connectors either.

There are tests you can do once the repeater system is installed by using a directional coupler in the antenna line to generate a weak signal into the repeater. You turn the transmitter off and test the SINAD level. Then do the same with the transmitter on as the repeater would normally operate. If there is no change in SINAD then your good. With the components you are considering expect some degradation when the transmitter comes on, which will cover up weak signals and limit the usable range.

And if its a low level repeater get a bigger antenna.

PRCGuy, Thank you for the info! It amazes me how much there is to know about this stuff. It's been an education!
 

kayn1n32008

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The duplexer the OP is asking about is a 4 cavity BpBr. It appears to be sized between a Sinclair mobile ‘flat-pack’ notch duplexer and a Q3220C ResLoc.
 

Project25_MASTR

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That would be an interesting site to link to...

My personal favorite flat pack duplexer is the Epcom (Made in Mexico) flatpacks. They are lower in cost (~$100 less) and use better components than the RFS (Celwave) flatpacks. Like other 50W rated flat packs, don't expect to push more than 30W through them before you desense.
 

prcguy

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That should work fine at 50 watts and it will provide some needed band pass. Unless the repeater RF section is really bad it should make for an ok system. If this is going any where close to other radios or towers, etc, it should also have an isolator. Its a good idea even if this is a home repeater, it will give the transmitter and part of the duplexer a good 50 ohm match and will protect the transmitter if the antenna match goes wild. You can sometimes find good UHF isolators on Ebay for under $75 with load.

The duplexer the OP is asking about is a 4 cavity BpBr. It appears to be sized between a Sinclair mobile ‘flat-pack’ notch duplexer and a Q3220C ResLoc.
 

kayn1n32008

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That would be an interesting site to link to...

My personal favorite flat pack duplexer is the Epcom (Made in Mexico) flatpacks. They are lower in cost (~$100 less) and use better components than the RFS (Celwave) flatpacks. Like other 50W rated flat packs, don't expect to push more than 30W through them before you desense.
 

prcguy

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For less than that duplexer you can usually get a used PD/Celwave 526 series pass/reject duplexer with 6 cavities and 120dB rejection. It doesn't get much better than that.

 

smokey222

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For less than that duplexer you can usually get a used PD/Celwave 526 series pass/reject duplexer with 6 cavities and 120dB rejection. It doesn't get much better than that.
Thank you for the reply.
 
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