Hi folks. Batboard forums have come through in the past some I'm hoping you can help me out.
I have an MSF5000 Limited VHF Repeater with a Fiplex 4 cavity duplexer. Antenna is a Comet GP-2. It's gone to the shop to get the front end "preselector" aligned but I'm being told from several hams that the sensitivity is still not there. The duplexer checked out, it's properly tuned/aligned. I'm not convinced the preselector is up to snuff. With that said, is there any way to bypass the internal preselector completely?
MSF5000 2 Meter Issues
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Re: MSF5000 2 Meter Issues
There is no cheap way to get a repeater working well. Fiberglass antennas are not suitable for repeater use and a VHF / UHF combination antenna is a no no. The antenna you indicate is advertised as a base antenna. This does not mean that it is suitable for repeater use where the receiver is listening while the transmitter is keyed. This also applies to the feedline. Only use solid feedlines like Andrews Heliax etc., do not use LMR type cables, these will eventually create noise and desense the receiver for a variety of reasons. Again, the manufacturer only suggest to use these cables for base use, not repeater use.The four cavity duplexer if tuned for the required 500 KHz separation provides 80 dB isolation according the spec sheet; 90 dB would really be desirable, but the pre-selector in the MSF does help some.
All the above items need to be top notch in order to reduce noise/desense and optimize sensitivity. Without test equipment, an easy way to check for desense is to listen for a weak signal using a plugin handset while turning the transmitter on and off.
Forgot to mention, tuning of the pre-selector is child play for a respectable shop. They could have provided you with some indication of the sensitivity. My guess is that they likely did OK.
Nand.
All the above items need to be top notch in order to reduce noise/desense and optimize sensitivity. Without test equipment, an easy way to check for desense is to listen for a weak signal using a plugin handset while turning the transmitter on and off.
Forgot to mention, tuning of the pre-selector is child play for a respectable shop. They could have provided you with some indication of the sensitivity. My guess is that they likely did OK.
Nand.
Re: MSF5000 2 Meter Issues
I'm betting aside from Nand's spot-on diagnosis (nice to see you around again, Nand), that your Fiplex duplexer isn't capable of handling the 600kHz split, and your transmitter is talking to your receiver to some degree. Is the Fiplex unit actually rated for 600kHz spacing? Is this a real-deal large cavity duplexer, or a wide-space rackmount job that's meant for commercial use? If it's the one Motorola sells, it's not gonna cut it at 600kHz.
Or are you using an odd-split?
Or are you using an odd-split?