Hoping I can get a few questions answered here. I recently built my first repeater and just started off with a cheap Chinease notch style duplexer. When I got the repeater online and did a few range tests I noticed the transmit range was about 12 miles but the receive range was less than a mile. After talking to a few people in my local repeater group I was told to ditch the notch style duplexer for a more favorable cavity style duplexer. I got on Ebay and found this Phelps Dodge 4 cavity duplexer model 696 and had it tuned for my repeater frequency. When I received it I hooked it up and got some strange results. When an SWR meter is hooked up to it between the transmit side of the repeater and the duplexer I was now getting 40 watts out of the repeater at the back of the repeater instead of the 48 watts i was getting with the notch duplexer 1.13 swr at the back of the repeater box. When I moved the meter to the end of the jumper cable and screwed the meter into the duplexer side I got 36 watts still connected between the repeater and duplexer 1.28 swr at this point. I then moved the meter to the antenna output at the tee connector on the duplexer and got the same wattage as I was getting on the input side at the duplexer 36 watts except now I was getting 1.01 swr. I then thought it was tuned poorly so I connected my VNA to it and found it was slightly out of tune and did a slight adjustment following the original tuning instructions I found on the repeater builder website and the numbers didn't really change. I then started looking at the cables between the cavities and found that a couple of the connectors were loose and one was failing so i replaced the 1 end paying close attention to not change the length of the cable as apparently it changes the performance of the duplexer adversely, the cables from the end cavities to the tee were electrical taped at the ends for some reason so I removed the electrical tape and they seemed firm. Other things to mention that might be helpful are the repeater is a Kenwood TKR 850-1 and the Antenna is a Comet 712-EFC. The jumper cable used between the repeater and duplexer's transmit side is a 36" piece of lmr400 with N connectors on both ends, the receive cable is a piece of RG-142 with an N connector on 1 end and an N on the other. No adapters are used on the jumpers. On the antenna side I am using LMR400 with an adapter from so239 to N on the duplexer side, N connecter on the antenna side. " I know I know" I need Heliax but I need to save up for the feedline, I should have it in place next month. The cables used between the cavities are pieces of RG-8U, on the Celwave version of this duplexer the cables are supposed to be RG-214 but I have seen some pictures of this duplexer on Ebay and they all seem to use RG-8U on the cavity cables. and according to the Celwave spec sheet for this duplexer the measured lengths of the cables are all correct. So my questions are: 1. are those reading normal from the SWR meter? I know there is usually loss through a duplexer but this seems weird. 2. Should I look into changing these cavity cables out due to poor fittings and electrical tape? 3. Are the jumper cables I have chosen ok for their purpose or should I change those out to something different. 4. Is the LMR400 to the antenna affection the duplexer performance? Oh and my range did change slightly, not nearly as much as I had hoped.
You can post now and register later.
If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.
Question
Colin927
Hello all,
Hoping I can get a few questions answered here. I recently built my first repeater and just started off with a cheap Chinease notch style duplexer. When I got the repeater online and did a few range tests I noticed the transmit range was about 12 miles but the receive range was less than a mile. After talking to a few people in my local repeater group I was told to ditch the notch style duplexer for a more favorable cavity style duplexer. I got on Ebay and found this Phelps Dodge 4 cavity duplexer model 696 and had it tuned for my repeater frequency. When I received it I hooked it up and got some strange results. When an SWR meter is hooked up to it between the transmit side of the repeater and the duplexer I was now getting 40 watts out of the repeater at the back of the repeater instead of the 48 watts i was getting with the notch duplexer 1.13 swr at the back of the repeater box. When I moved the meter to the end of the jumper cable and screwed the meter into the duplexer side I got 36 watts still connected between the repeater and duplexer 1.28 swr at this point. I then moved the meter to the antenna output at the tee connector on the duplexer and got the same wattage as I was getting on the input side at the duplexer 36 watts except now I was getting 1.01 swr. I then thought it was tuned poorly so I connected my VNA to it and found it was slightly out of tune and did a slight adjustment following the original tuning instructions I found on the repeater builder website and the numbers didn't really change. I then started looking at the cables between the cavities and found that a couple of the connectors were loose and one was failing so i replaced the 1 end paying close attention to not change the length of the cable as apparently it changes the performance of the duplexer adversely, the cables from the end cavities to the tee were electrical taped at the ends for some reason so I removed the electrical tape and they seemed firm. Other things to mention that might be helpful are the repeater is a Kenwood TKR 850-1 and the Antenna is a Comet 712-EFC. The jumper cable used between the repeater and duplexer's transmit side is a 36" piece of lmr400 with N connectors on both ends, the receive cable is a piece of RG-142 with an N connector on 1 end and an N on the other. No adapters are used on the jumpers. On the antenna side I am using LMR400 with an adapter from so239 to N on the duplexer side, N connecter on the antenna side. " I know I know" I need Heliax but I need to save up for the feedline, I should have it in place next month. The cables used between the cavities are pieces of RG-8U, on the Celwave version of this duplexer the cables are supposed to be RG-214 but I have seen some pictures of this duplexer on Ebay and they all seem to use RG-8U on the cavity cables. and according to the Celwave spec sheet for this duplexer the measured lengths of the cables are all correct. So my questions are: 1. are those reading normal from the SWR meter? I know there is usually loss through a duplexer but this seems weird. 2. Should I look into changing these cavity cables out due to poor fittings and electrical tape? 3. Are the jumper cables I have chosen ok for their purpose or should I change those out to something different. 4. Is the LMR400 to the antenna affection the duplexer performance? Oh and my range did change slightly, not nearly as much as I had hoped.
Thanks in advance
Colin.
9 answers to this question
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.