Batboard

Seeking feedback on performance of VHF compact base station duplexers.

Our landlord has advised use to get our old 6 can unit off of the floor. We're thinking of installing a taller cabinet and using a rack mounted compact duplexer instead.

Anyone out there ever used one with good results? I see there are 4 cavity and 6 cavity versions sold by Telewave.

Thanks.

No such thing as a free lunch. If you want small cavities, you can compromise in a few ways:
Less power handling
More minimum separation
More insertion loss
Less isolation

The 6-can compact duplexer from Telewave is 2.5dB insertion loss. For comparison, the 500KHz spacing, 150 watt pass/notch duplexer I just purchased from EMR is only 2.3dB insertion loss, and that's with a dual-stage isolator in the picture. Also, the EMR duplexer provides 90+dB of isolation minimum (I usually see 10-20dB more than that).

I also question the 350-watt rating on those units... I'd be rather concerned about dumping a quarter K or more into a compact duplexer like that continuously. It might work, but I'd be seriously concerned about the amount of heat generated and its effect on the longevity of the duplexer itself as well as everything else in the cabinet.

If you're considering going to a taller cabinet, most of the real duplexers are constructed to fit into a standard 19" rack, but in a vertical configuration (you have to make sure your rack is deep enough if you go with a honking big unit.) In a 6' cabinet, you should be able to install a battery bank (I usually use 2 150Ah AGM UPS batteries), a shelf for the duplexer, repeater (usually a TKR-750 for me), and a power amp (Crescend).

Tell your landlord that nice big duplexer is part of what keeps us, as well as the other site customers, from complaining about intersite interferance, both from and to others.

These little compact units can do an "okay" job in some places. They were never meant for typical 24/7 remote site, nor were they meant for keeping out adjacent channel interferance.


Don't you have some alternative, like take apart the duplexer assembly and install the cavities in a cabinet, hang them from the wall?

Stick with the duplexer you have. Compact duplexers are not equal to full size duplexers in a multi base / repeater enviroment.

Consider remounting the cans that you have into a different configuration. Don't change cable lengths or cable.

Good Luck , Bob

You should provide more specifics about your operation including the make and model of your repeater, transmit power, TX and RX frequencies [or at least the separation], whether or not you have a receive pre-amp, as well as the manufacturer and model number of your current duplexer.

It is possible that your operation - if there is enough frequency separation - is not using the maximum capability of your current duplexer. In some cases a smaller duplexer could provide similar isolation and meet your needs - saving a lot of space without compromising performance.

Have you considered looking up and trying to mount the cans from the ceiling. In most radio rooms, that area is just plain open waisted space. Even the site owners don't consider it usable.

Jim

railtrailbiker wrote:Seeking feedback on performance of VHF compact base station duplexers.

Our landlord has advised use to get our old 6 can unit off of the floor. We're thinking of installing a taller cabinet and using a rack mounted compact duplexer instead.

Anyone out there ever used one with good results? I see there are 4 cavity and 6 cavity versions sold by Telewave.

Thanks.

We have a bunch of TX/RX 28-35-15C 6-can 19" rack-mount compact VHF highband duplexers in service here. Uses 12" of rack space. We mainly have them on small-shelter mountaintop sites and sites that require short cabinets or a small cabinet footprint (lookout towers, etc.).

These duplexers aren't advertised in their catalog so we've had trouble ordering them from time to time due to various salespeople that didn't know of its existence. I talked to a salesperson about a year ago and he said they had no plans at discontinuing the product.

At a 0.775 MHz split the duplexer nominally has about 2.15dB insertion loss with -115dB attenuation on TX and RX ports and has attenuation of 65dB between TX and RX ports. So what you lose on this duplexer is some insertion loss and less attenuation between TX and RX compared to the larger ones. If you have a very selective receiver (i.e. Micor, Quantar) and can afford to lose some TX power through the duplexer, this may work out good for you.

This duplexer has proven to be a very reliable product - our shop has had this type of duplexer in service for over 20 years with very little trouble.

At 'busy' colo sites we still use compact duplexers in some cases, but as with any duplexer they're always accompanied by a dual-stage isolator followed by at least 1 cavity resonator on the TX side and at least 1 cavity on the RX side, depending on what's required as a result of the site's intermod study.