Duplexer Suggestion

[BlueDevil]

I am looking for suggestions for a duplexer to be used in a new VHF conventional analog system with a repeater TX frequency of 151.8950 and a repeater RX frequency of 159.9150. It will be in close proximity to an existing VHF conventional analog repeater operating on a repeater TX frequency of 155.1750 and repeater RX frequency of 153.7775. The existing repeater is a Motorola XPR8300 and transmits at 50watts and uses a Station Master Omnidirectional antenna with a Telewave 1554 bandpass duplexer.

I haven't purchased the repeater for the new system yet. It is licensed for 50watts and that's what I have been looking at. I am looking at a 2 element folded dipole antenna operating perpendicular or at 90 degrees from the Omnidirectional Station Master. Do I need a full bandpass/bandreject duplexer or would a bandpass/notch duplexer provide adequate isolation from the existing system?

 

[kayn1n32008]

Sinclair Q2223(?). 6 cavity ResLoc with notch capacitors.

FYI, XPR8300 repeater is only 25w max.

 

[BlueDevil]

I will take a look at the Sinclar option.

 

[N2AL]

Sinclair Q2223(?). 6 cavity ResLoc with notch capacitors.

FYI, XPR8300 repeater is only 25w max.

I will take a look at the Sinclar option.

I have to agree with kayn1n32008 -Sinclair's are amazing! My Elmer now uses Sinclair's on his machine, and as compared to other brands we see a positive difference using Sinclair.

Just my two cents and BlueDevil I wish you the best of luck with your VHF endeavors.

 

[prcguy]

Don't forget an isolator on the transmitter output before the duplexer. This will reduce the chance of your transmitters talking to each other and creating Intermod, plus it will protect your transmitter if the antenna or duplexer goes south.
prcguy

 

[BlueDevil]

Thanks prcguy!

 

[RFI-EMI-GUY]

I would certainly recommend a duplexer that employs bandpass characteristics on the receiver port. I encountered a repeater (45 MHz LOW BAND) that had spurious receiver responses 31 MHz below the operating frequency. The receiver was getting hammered by TX noise that was down at 14 MHz. The duplexer was a TX-RX pseudo bandpass and at the out of band spurious frequency there was virtually no rejection. A Sinclair BP duplexer did work. As far as RX band reject, you are going to have to somehow consider near by high power base stations as well as your own. And as others mentioned, the transmitter should have an isolator panel and tuned reject not only noise to its own RX, but keep other high power stations from entering. VHF is a mess.

 

[RFI-EMI-GUY]

(snip) I am looking at a 2 element folded dipole antenna operating perpendicular or at 90 degrees from the Omnidirectional Station Master. (snip)

Can you explain what you are trying to do with the antenna?

 

[BlueDevil]

Well the existing omnidirectional Station Master does a good job covering the area we need. The new repeater is only going to be needed to cover a specific area and needs to have a much larger beamwidth to cover the area that we need. I cannot vertically separate the antennas at all and can only offer minimal horizontal separation. So I figured I could at least orient them so the radiation patterns would have the least amount of interference. It probably doesn't matter that much but at least it's something...