Re: [Repeater-Builder] New system's in, but a few problems
At 1/29/2006 11:37 PM, you wrote: About 8 years ago, I tried using a Comet GP-9 antenna combined to serve two repeaters, one on 2 meters the other on UHF. I found the GP-9 worked FAR better on 2 meters than on 445 MHz. I was running good GE Mastr Pro repeaters, good pass/reject duplexers, good ARR GaAsFET pre-amps, and had NO desence. The comet GP-9 simply is not very good for UHF. Of course, the water you foung in the antenna is not good either. My experience has been quite different, as I've found the GP9 to be overall a very good UHF antenna. I have a 2 meter 440 system running off of one in a very similar layout to yours (antenna only a few feet above the equipment); the 440 outperforms 2 meters as expected. No desense on either band. There is a DB-408 at the site that we once tried but the GP9 outperforms it as well. Bob NO6B Yahoo! Groups Links * To visit your group on the web, go to: http://groups.yahoo.com/group/Repeater-Builder/ * To unsubscribe from this group, send an email to: [EMAIL PROTECTED] * Your use of Yahoo! Groups is subject to: http://docs.yahoo.com/info/terms/
RE: [Repeater-Builder] New system's in, but a few problems
-Original Message- From: Repeater-Builder@yahoogroups.com [mailto:[EMAIL PROTECTED] On Behalf Of Bob Dengler Sent: Monday, January 30, 2006 12:43 PM To: Repeater-Builder@yahoogroups.com Subject: Re: [Repeater-Builder] New system's in, but a few problems At 1/29/2006 11:37 PM, you wrote: About 8 years ago, I tried using a Comet GP-9 antenna combined to serve two repeaters, one on 2 meters the other on UHF. I found the GP-9 worked FAR better on 2 meters than on 445 MHz. I was running good GE Mastr Pro repeaters, good pass/reject duplexers, good ARR GaAsFET pre-amps, and had NO desence. The comet GP-9 simply is not very good for UHF. Of course, the water you foung in the antenna is not good either. My experience has been quite different, as I've found the GP9 to be overall a very good UHF antenna. I have a 2 meter 440 system running off of one in a very similar layout to yours (antenna only a few feet above the equipment); the 440 outperforms 2 meters as expected. No desense on either band. There is a DB-408 at the site that we once tried but the GP9 outperforms it as well. Bob NO6B Mine has been just the opposite of Bob's, and in fact, I'm using the same antennas! I had a GP9 top-mounted on a tower, my UHF repeater and an APRS digipeater on it. The GP9 developed crackling noises after about a year of use. I and the owner of the APRS digi decided to put up separate antennas - mine a DB408 replacing the GP9 on top of the tower, and his a DB224 side-mounted below it. When we got the GP9 down, we didn't find anything obvious wrong with it, either internally or externally, and the guy with the APRS digi took the antenna and is now using it for something else. The DB408 (ham-cut version) plays much better than the GP9 ever did. As usual, YMMV. --- Jeff Yahoo! Groups Links * To visit your group on the web, go to: http://groups.yahoo.com/group/Repeater-Builder/ * To unsubscribe from this group, send an email to: [EMAIL PROTECTED] * Your use of Yahoo! Groups is subject to: http://docs.yahoo.com/info/terms/
RE: [Repeater-Builder] New system's in, but a few problems
Hmm, I don't know what to say. I tried 2 different GP-9's had the exact same performance. I then replaced the GP-9 with a Diamond the UHF performance immediately improved, became a close match to the 2 meter. -- Original Message -- Received: Mon, 30 Jan 2006 11:54:23 AM CST My experience has been quite different, as I've found the GP9 to be overall a very good UHF antenna. I have a 2 meter 440 system running off of one in a very similar layout to yours (antenna only a few feet above the equipment); the 440 outperforms 2 meters as expected. No desense on either band. There is a DB-408 at the site that we once tried but the GP9 outperforms it as well. Bob NO6B Yahoo! Groups Links * To visit your group on the web, go to: http://groups.yahoo.com/group/Repeater-Builder/ * To unsubscribe from this group, send an email to: [EMAIL PROTECTED] * Your use of Yahoo! Groups is subject to: http://docs.yahoo.com/info/terms/
[Repeater-Builder] New system's in, but a few problems
Overall real performance isn't where I'd like it to be, I suspect the antenna is bad. We'll try changing it out later this week. We have some other more interesting symptoms, which I'd like to hear opinions on, but let me describe the system: Comet GP-9 dual band antenna. Can't change to a different type. When we took it apart back in december, it was wet inside. The antenna ends up being about 6' above my head, when I'm in this room on top of the building with the repeater. Hollow tile construction, so I suspect we are illuminated pretty well when we are transmitting. About 30' of FSJ1-50 feedline from the antenna to a comet band splitter, with HF port terminated. I could shorten it to maybe 25' but mechanically, that's what it takes. 2' of FSJ1-50 from the band splitter to Wacom four can BPBR set for UHF. 50W up the pipe on UHF 3' FSJ1-50 from the band splitter to the Wacom four can BPBR set for VHF. 18W up the pipe on VHF. I measured sensitivity using a 50dB tap inserted between the band splitter and the antenna, at the splitter common port. 50dB attenuation there, plus 20dB pad on my generator (for insurance) gave me the following values: Break squelch on VHF: -57dBm on generator Close squelch on VHF: -59dBm Break Squelch on UHF: -56dBm Close squelch on UHF: -61dBm That works out to -127dBm, -129dBm, -126dBm, and -131dBm respectively. The old system that I replaced had some desense, and needed the generator at -42dBm to hold solid with the same test configuration. So on VHF, I am measuring about 15dB better receive performance, but driving around, things seem not all that different. Of course the thing that's between the measurement point and the driving test is the antenna. Taking the VHF transmitter on and off, I don't see any desense on VHF. The UHF transmitter though, does desense the VHF rx some. It's a crystalled transmitter, with two helical filters internally before the final amplifier. VHF dosen't desense the UHF receiver. Looking at the VHF receiver port with a spectrum analyzer, I see some loud noises up at 160-170 MHz. My sinclabs filter knocks those out nicely, but gives no improvement in receive sensitivity. I also tried a preamp with it's own 5 section helical filter, that I'd measured at 16dB gain. This also gave no change in sensitivity with or without the sinclabs filter in front of it. I think this is telling me that I have a noise problem getting into the receiver, that is keeping me from seeing improvements made below that level. Also when tuning the VHF notch sliders on the receive side, I noticed that the first can (closest to the antenna) gave no real distinct improvement in white noise on a weak signal. The second can gave a very distinct improvement. Adjusting the notches on the TX side with transmitter on gave no real improvement. This seems to be telling me something about where my noise source is getting in. All connectors are wrench tight, all cables are new hardline, and have been swept. Given that I'm so close to the antenna, and I cannot change or move the antenna, other than to replace it with a visually identical antenna, what can I do to reduce the RF level in the room? The plumbing's as tight as I can make it, I think. I am also getting an audio squeal on the UHF side, which is not present when the controller is outputting, but is there on received audio. If I use the controller's record and playback function, then I can hear the squeal on my playback. I think most of this is caused by the UHF signal lighting up the whole room pretty well. I can try some better shielding on the audio and control signals.. I'm also thinking that if the antenna is bad, it might be radiating more straight down for some reason, than it normally would. Yahoo! Groups Links * To visit your group on the web, go to: http://groups.yahoo.com/group/Repeater-Builder/ * To unsubscribe from this group, send an email to: [EMAIL PROTECTED] * Your use of Yahoo! Groups is subject to: http://docs.yahoo.com/info/terms/
Re: [Repeater-Builder] New system's in, but a few problems
About 8 years ago, I tried using a Comet GP-9 antenna combined to serve two repeaters, one on 2 meters the other on UHF. I found the GP-9 worked FAR better on 2 meters than on 445 MHz. I was running good GE Mastr Pro repeaters, good pass/reject duplexers, good ARR GaAsFET pre-amps, and had NO desence. The comet GP-9 simply is not very good for UHF. Of course, the water you foung in the antenna is not good either. -- Original Message -- Received: Mon, 30 Jan 2006 12:47:34 AM CST From: Dave VanHorn [EMAIL PROTECTED] SNIP Comet GP-9 dual band antenna. Can't change to a different type. When we took it apart back in december, it was wet inside. SNIP So on VHF, I am measuring about 15dB better receive performance, but driving around, things seem not all that different. Of course the thing that's between the measurement point and the driving test is the antenna. SNIP Yahoo! Groups Links * To visit your group on the web, go to: http://groups.yahoo.com/group/Repeater-Builder/ * To unsubscribe from this group, send an email to: [EMAIL PROTECTED] * Your use of Yahoo! Groups is subject to: http://docs.yahoo.com/info/terms/
