Where doi i put the Transmit and recieve lines into the duplexer?

[centuryvrproductions]

I hae a mobile duplexer and its tuned to 444.5 and 449.5.

There is 3 connecters, the high, low and antenna. Which one (High/Low) do i put the transmitter and reciever to. (I transmitt on 444.5MHz)

A bit confusing and i just dont want to ruin anything by hooking it up wrong,

 

[zz0468]

The 'high' and 'low' labels refer to frequency. Which of the two frequencies is higher? Which of the two frequencies is lower? Connect accordingly.

 

[centuryvrproductions]

so i put the transmit radio on low because its on 444.5 and recieve on high because its 449.5?

im confused becuase does the low mean it blocks the high or it passed the high. same for high

 

[zz0468]

so i put the transmit radio on low because its on 444.5 and recieve on high because its 449.5?

im confused becuase does the low mean it blocks the high or it passed the high. same for high

The "low" means it's the low frequency port. The "high" means it's the high frequency port. Forget for now what it blocks. If it says "low" that's the lower frequency of the pair. Period. It's not that complicated.

 

[wa8pyr]

so i put the transmit radio on low because its on 444.5 and recieve on high because its 449.5?

im confused becuase does the low mean it blocks the high or it passed the high. same for high

I assume you're trying to build a repeater, correct?

What you probably have there is a simple bandpass filter, which passes the high frequency on the high side of the duplexer and passes the low frequency on the low side. They tend to be somewhat more reliable in mobile applications than BpBr (bandpass/band reject) duplexers which have more fiddly bits and are trickier to tune.... and Bp duplexers are cheaper. They also tend to be less reliable at higher power levels. Don't try to pump too much power through that thing, though; the more power you put in will cause higher desense on the receive side; you could even toast the duplexer or your transmitter, or both. Most of those surplus mobile duplexers are rated around 50 watts, but I would never put more than 25-30 watts into one.

In any case, it's just like zz0468 said; connect the high frequency side of your system to 'high' and the low side to 'low'. Be sure to use good quality low-loss (preferably double-shielded) cables between the transmitter, receiver and duplexer. If the duplexer has SO239 connectors, use the best PL259 plugs you can find (preferably silver plated with gold center connectors and teflon dielectric) and make sure they stay nice and tight. Also, your connecting cables really should be an electrical 1/4 wavelength at the frequency of operation.

Here's a really good tutorial on duplexers:

Duplexers: Theory and Tune Up

That all being said, those surplus mobile duplexers make dandy portable repeaters; I put one together for emergency use using a couple of Motorola Radius transceivers, a simple controller, and one of those mobile duplexers. Worked like a charm.

 

[centuryvrproductions]

ya, Thanks for the info... Im just making sure. I figured i had it right but better safe than sorry,

I bought the duplexer new for like $100 on ebay with shipping and its rated for 50w. Im currently running about 25-30 watts from the radio.

The repeater is a Motorola desktrac Spectra modified for maxtracs so thats what i am running


The KB1VSP Repeater

 

[prcguy]

Mobile duplexers are generally notch only and the bandpass is so wide its to be ignored.

The cables between cavities are usually 1/4 wavelength or multiples (minus velocity factor) but that includes the length and effects of the coupling loops, so the cables will be somewhat shorter.

The cables between the radio equipment and the duplexer do not have to be multiples of 1/4 wavelength and are not critical
prcguy

I assume you're trying to build a repeater, correct?

What you probably have there is a simple bandpass filter, which passes the high frequency on the high side of the duplexer and passes the low frequency on the low side. They tend to be somewhat more reliable in mobile applications than BpBr (bandpass/band reject) duplexers which have more fiddly bits and are trickier to tune.... and Bp duplexers are cheaper. They also tend to be less reliable at higher power levels. Don't try to pump too much power through that thing, though; the more power you put in will cause higher desense on the receive side; you could even toast the duplexer or your transmitter, or both. Most of those surplus mobile duplexers are rated around 50 watts, but I would never put more than 25-30 watts into one.

In any case, it's just like zz0468 said; connect the high frequency side of your system to 'high' and the low side to 'low'. Be sure to use good quality low-loss (preferably double-shielded) cables between the transmitter, receiver and duplexer. If the duplexer has SO239 connectors, use the best PL259 plugs you can find (preferably silver plated with gold center connectors and teflon dielectric) and make sure they stay nice and tight. Also, your connecting cables really should be an electrical 1/4 wavelength at the frequency of operation.

Here's a really good tutorial on duplexers:

Duplexers: Theory and Tune Up

That all being said, those surplus mobile duplexers make dandy portable repeaters; I put one together for emergency use using a couple of Motorola Radius transceivers, a simple controller, and one of those mobile duplexers. Worked like a charm.

 

[jim202]

I hae a mobile duplexer and its tuned to 444.5 and 449.5.

There is 3 connecters, the high, low and antenna. Which one (High/Low) do i put the transmitter and reciever to. (I transmitt on 444.5MHz)

A bit confusing and i just dont want to ruin anything by hooking it up wrong,

If you have to ask how to hook up the duplexer, then I would suggest that you step back and go do some homework on the device. As one person mentioned, the cables that go between the cavities are frequency dependent. Unless you bought this unit brand new from the company that made it and had them tune it for you, your in for a real ride.

The use of any cavity in a radio antenna system needs to be tuned to the frequencies it will be used on. If you obtain a used unit, then it will have to be tuned to the operating frequency that you will use it on. The cables will probably have to be re0laced with new ones that match the frequencies you will use the duplexer on.

You mentioned a 444.xxx and a 449.xxx frequency, so it is in the ham band. Being that you bought this unit from someone else, the chances that it was used up on the 460 MHz range are very good. the original frequencies may even be marked or on a sticker on the cavities. Either way, you will have to retune them to your channels. This will require some test equipment and 3 coax attenuators to do the tuning correctly.

There have been a ton of threads on how to tune duplexers all over the internet. I would suggest that you spend some time finding these and reading them. I am not trying to be hard on you, but after being in this field for over 45 years now, I have seen some rookies make a mess of some real fine cavities, because they though they knew what they were doing. Please take the time and read before you flounder your way into trying to move the duplexer down to the ham band.

 

[davidgcet]

if it is the black celwaves with the rigid tubing conencting the cans then there are no cables to replace. i would highly recommend having them professionally tuned unless you have the proper equipment. you CANNOT tune these by using the radio and just listening/watching a wattmeter. if tuned properly these have very low loss since they are such wide pass, but the drawback is it can dump full power over to the RX very quickly if you get it out of tune and this will blow out your front end.