2 repeater 1 Duplex Filter

[riodda]

Hi all, i'm building a cheap portable repeater based on 2 GM-338, for that i've buyed on ebay an used 100W 6 cavities duplex filter and i have a couple of questions:
1. What are the drawbacks of haveing a 100W duplexer and 30W TV radio ?
2. Since the duplexer is oversized may i share it with a second repeater (provided it's on frequencies that are in the duplexer range) ? Do i need to add other hardware or i just connect 2 TX radio on the duplexer imput ?

Thanks.

 

[Voyager]

1. No drawbacks at all. In fact, it should work better than one rated lower since there is more isolation.

2. You cannot do that. You would be sending RF into the other TX which will cause a lot of RF noise and could damage both transmitters.

 

[riodda]

1. No drawbacks at all. In fact, it should work better than one rated lower since there is more isolation.

2. You cannot do that. You would be sending RF into the other TX which will cause a lot of RF noise and could damage both transmitters.

A Band pass filter between the TX radios and the duplexer will not work either i guess, i've read somware about a CAVITY TRANSMITTER COMBINER, will it do the trick or the loss will be too big ?
Thanks.

 

[kayn1n32008]

Hi all, i'm building a cheap portable repeater based on 2 GM-338, for that I've buyed on ebay an used 100W 6 cavities duplex filter and i have a couple of questions:
1. What are the drawbacks of having a 100W duplexer and 30W TV radio ?
2. Since the duplexer is over sized may i share it with a second repeater (provided it's on frequencies that are in the duplexer range) ? Do i need to add other hardware or i just connect 2 TX radio on the duplexer input ?

Thanks.

Hi riodda,

As voyager stated, there is no drawback using a duplexer rater for 100w on a 30w transmitter.

As for using the single duplexer with more than one repeater, things get significantly more complicated.

You will need 2 more pieces of equipment. The first piece of equipment is called a transmitter combiner. There are different types of combiners. The right combiner depends on how close in frequency your transmitters are. Generally if you are trying to use a single duplexer you will need something similar to http://www.sinclairtechnologies.com/catalog/resources/pdf/TC3212-DM.pdf (depending on band, this one is UHF.)

That takes care of the transmitters. In order to have more than one receiver you will also need a receive multicoupler something like http://www.sinclairtechnologies.com/catalog/resources/pdf/RM3(AA-W)(BB)G(Y)(C)-DM.pdf (depending on band, this one is UHF)

Keep in mind the transmit combiner, receive multicoupler, and duplexer all need to be properly tuned to the specific frequency pairs you wish to use.

 

[Voyager]

Yes, a transmitter combiner will work provided the TX frequencies are far enough apart. You can then use a bandpass filter on the receiver (provided they are in the same band segment) using a separate antenna and multicoupler. In this case, you are only limited by the power rating of the TX antenna and total combined power as to how many repeaters you can add.

 

[kayn1n32008]

A Band pass filter between the TX radios and the duplexer will not work either i guess, i've read somware about a CAVITY TRANSMITTER COMBINER, will it do the trick or the loss will be too big ?
Thanks.

Once you start combining transmitters, you will see, at minimum, 3db of loss between the input of the combiner and the output. You will want, at minimum 70db of isolation between ports of the combiner.

 

[bill4long]

How many watts will your transmitters be outputting?

 

[prcguy]

If the two repeater frequencies are close together like 50KHz then you could use a hybrid combiner with isolaters that doesn't need cavities. As someone mentioned this type combiner will loose at least half the transmit power in each transmitter and you also have to split the receive port from the duplexer which will loose at least half the receive level. With more hardware like a good preselector cavity and a good preamp you could make up for the receive loss.

All the hardware mentioned is not cheap and you two separate duplexers and antenna systems is probably easier and less expensive.
prcguy

 

[riodda]

Thanks for the answers, i will go for a second duplexer then. Thanks

 

[bill4long]

Thanks for the answers, i will go for a second duplexer then. Thanks

You didn't answer my question: how much output power on the transmitters?

If it's 50 watts or under, you can find cheap brand-new Jeisei UHF mobile duplexers on EBay for $100 or less each. (Make sure you get the 50 watt one, not the 35 watt one, unless you intend to run 35 watts or less.) They are knock-offs of Celwaves. I have two of them that work full duty (transmitting 100% of the time typically) and they work just fine. They will tune them for you before shipping.

 

[riodda]

You didn't answer my question: how much output power on the transmitters?

If it's 50 watts or under, you can find cheap brand-new Jeisei UHF mobile duplexers on EBay for $100 or less each. (Make sure you get the 50 watt one, not the 35 watt one, unless you intend to run 35 watts or less.) They are knock-offs of Celwaves. I have two of them that work full duty (transmitting 100% of the time typically) and they work just fine. They will tune them for you before shipping.

The radios are 30W and the duty cicle will be very small (it's a motorsport application) about 10-15%.
I'm will have a look to the Jeisei you mentioned, the one i got was a cellwave 100W i got it for 120€ i could not find enything cheaper on the net.
Thanks.

 

[cmdrwill]

Go with two separate repeater/duplexer/antenna units. And place them away from each other.

 

[K5MPH]

Yes go with the second duplexer..........