Thanks so much Joe. I think your recommendation on filtering the output of the UHF repeater seems to make good since to me. We will start there. The duplexer is one of the smaller units as compared to the larger cans I have seen for UHF. I guess it is different designs. I know I have seen some UHF duplexers at Hamfest that where much smaller than our two meter stuff of course, but still much larger than the unit we are using. I don't know the difference, I assumed just different design technology, and not necessarily bigger is better. If I am wrong on that part, please let me know, because I have access to a UHF duplexer, the 4 can type (probably 4"X8" or 10" tall, for a fairly small investment. I will first look into the exact filter you suggested. It makes since to me it is better to clean up the signal transmitted as much as possible anyway. Then we will follow your suggestions on the link radio receiver next as you have suggested if the problem persist. Thanks a billion to you and the group for all the help.
73 de John Godfrey KE5NZY BARC Pres. -----Original Message----- From: Repeater-Builder@yahoogroups.com [mailto:repeater-buil...@yahoogroups.com] On Behalf Of Joe Burkleo Sent: Sunday, May 03, 2009 1:42 AM To: Repeater-Builder@yahoogroups.com Subject: [Repeater-Builder] Re: Linking and interference problem John, Thanks for the more in-depth explanation. Link antenna and feedline is about as good as you can get. About the only improvement you might make is to get the two UHF antennas directly under each other. That creates a cone of silence and make for the best null. No need for the 7/8" other than a small improvement in signal loss. I would think about replacing all of the jumpers with silver plated double shielded coax. The filter that comes to mind for your link receiver would be a very precise crystal filter made for your link radio receive frequency. They are kinda pricey, so they may be out of your price range, but they are only a few KC wide. Since it sounds like the hub repeater is on a stable frequency and will most likely be there for a long time, the crystal filter makes sense. They are not re-tunable in the field since they are made for a very specific receive frequency. They have a little loss in them, but since you can run the squelch fully tight, you have enough headroom, and that should not be a problem. Other item I would recommend is to install a isolator on the UHF repeater transmitter before it gets to the duplexer. I am not sure what you are using for a duplexer, but I also might suggest locating a Telewave or similar 9" diameter to 12" diameter bandpass filter (one that has two connectors) to go between the UHF repeater transmitter and the duplexer. They use these large diameter UHF cavities for transmit combiners, but I have seen them on Ebay for reasonable prices from time to time. The larger diameter the cavity, the steeper the skirts on each side of the transmit frequency will be. I know this may sound backwards, but I would attack adding the isolator and additional filtering on the UHF transmitter as the first step. Once you have made the UHF repeater transmitter as clean as it can be, then you can move on to adding any additional filtering to the link receiver, if it is still needed. Joe - WA7JAW > Joe, Thanks for asking.. > > Question #1 link antenna is on top. 8 element yagi vertical pointed 210 SW > > Question #2 No. They are on different legs and each is on the other side of > the tower, almost directly opposite each other. > > Question #3 No preamp. > > Question #4 1/2 inch Andrews Heliax (not superflex) on both UHF units 150FT > on one 140Ft on the other. 3ft jumpers 9914 belden on each radio. same on > the Yagi's. N type connectors. Wish we could afford 7/8, but we take what > the club can afford and work with that. Our club has appox 50 members, > sometimes more or less depending on when they pay there dues. Hi HI. I know > you didn't ask, but just in case you needed to know, 7/8 is not an option > for us right now. > > Agreed that even just a few extra db rejection would do the trick. It > wouldn't take a lot I don't think based on the squelch test, but a few db I > would be highly thankful for, and I just don't have the knowledge to know > how to get there from here. (-: > > 73 de John Godfrey > KE5NZY BARC Pres. >
