Hi Eric. The machine I have is as you described as "the latter" - it employs a mobile-type, 6-resonator notch duplexer. It is on 452/457 MHz. As for the exact model designation, it says "Radius GR1225" on the front panel...
We've tried reversing the cables going to the duplexer, with no change in performance... I labeled the cables myself when we disassembled the unit to have the duplexer retuned, so I know which one was supposed to go where. I'm seriously beginning to think the duplexer is erroneously tuned to notch the RX freq on both sides. So in essence, there is no "high" and "low" notch, there is just "high". Mark - N9WYS -----Original Message----- From: Repeater-Builder@yahoogroups.com On Behalf Of Eric Lemmon Mark, Are we talking about the R1225 transceiver itself, or is the repeater actually a GR1225, RKR1225, or a GR400 or GR500 X-Pand repeater? If one of the latter, the duplexer is usually a "mobile notch duplexer" with six helical resonators in a one-inch-thick package. Does your R1225 repeater use such a duplexer, or is it a full-size BpBr unit with large cavity filters? When a service tech works mostly with BpBr cavities, it is a common error to tune the screws for the pass frequency instead of the notch frequency. A local hospital had a GR1225 repeater come back from a radio shop with the TX and RX cables reversed, and it wouldn't work very well. It tested fine on the service monitor, but the tech got confused about the "HIGH" and "LOW" labels on the notch duplexer. The ports should have been labeled "REJECT HIGH" and "REJECT LOW", with the former going to the TX output on the R1225 and the latter going to the RX input on the R1225. If the R1225 is a high-power (25-50 watt) model, it is possible that operating the transceiver with a mis-tuned notch duplexer can burn out the protection diodes in the RX front end. There is no tune-up required on the R1225. The RX front end is varactor-tuned by the CPU to optimize the RX sensitivity. The R1225 service manual is 6880905Z53, about $13, and is a "must-have" document. If your repeater is a GR1225, you also need the 6880904Z90 manual, also about $13. If your repeater is an RKR1225, you also need the 6880907Z10 manual, about $36. Finally, if your repeater is a GR400/GR500 X-Pand model, you also need the 6880905Z54 manual, about $13. Many early GR1225 repeaters were shipped with a duplexer harness made of RG58 single-shielded cable. I was setting up one such GR1225 on a VHF repeater pair with a 5.26 MHz split, and I was measuring almost 12 dB of desense. I cured the problem completely by making up a new harness using RG-400/U double-silver-shielded cable and the proper connectors on the ends- no adapters. That repeater is still in service after three years with no down time, but is being replaced with a new MTR2000 station. 73, Eric Lemmon WB6FLY -----Original Message----- From: Repeater-Builder@yahoogroups.com On Behalf Of n9wys A friend of mine has a Motorola R1225 repeater that is as deaf as a fence post. We've tried re-tuning the original duplexer and replacing it with another known-good duplexer. We even tried separating the antennas, although we could only get about 30' of vertical separation between the two. Nothing seems to work - and at 150mW on an HT, I can only get about 30' away from the repeater antenna before I cannot access it. 4W will give me a range of about 100 yds. Does anyone have the manual for this machine? If so, I'd be much obliged for a copy of any receiver tune-up procedures. I hate to think this thing is junk. Thanks in advance, Mark - N9WYS
