RE: [Repeater-Builder] Re: Antenna SWR = Desense?
I'm not far from Tim and have been emailing with him offline. Yesterday he disconnected the rx from the duplexer, terminated the rx port of the duplexer and injected weak signal directly into the receiver. He did not remove any original cables between the rx and duplexer, so he simply divided the rx path. When he ran another test he had no desense. This test should help prove / eliminate radiated antenna RF from 100ft away as the cause of his desense. He's describing pretty significant desense. It all works well ( without desense) into an end of feedline terminated dummy. I'm kinda questioning the quantar circulator somebody mentioned. He's planning the antenna site install soon. Don Kirchner W5DK -Original Message- From: Repeater-Builder@yahoogroups.com [mailto:repeater-buil...@yahoogroups.com] On Behalf Of Eric Lemmon Sent: Thursday, September 03, 2009 8:01 PM To: Repeater-Builder@yahoogroups.com Subject: RE: [Repeater-Builder] Re: Antenna SWR = Desense? Tim, A high-gain antenna that is only 100 feet away horizontally is far too close. It is bathing your repeater equipment with RF, and very few machines can tolerate being in such a high RF field. Vertical versus horizontal separation is very roughly in a 1:45 ratio, that is, the isolation of 100 feet of vertical separation is roughly equivalent to about 4,500 feet of horizontal separation. In other words, your 100 feet of horizontal separation is no better than if you put a mag-mount whip right on the top of the repeater cabinet. You would likely have less desense if you mounted your DB224 antenna on the roof of your equipment shed, directly above the repeater, so that the repeater cabinet was in the shadow beneath the antenna. You might also consider filtering the DC power leads to prevent RF ingress through that path. 73, Eric Lemmon WB6FLY -Original Message- From: Repeater-Builder@yahoogroups.com [mailto:repeater-buil...@yahoogroups.com] On Behalf Of tahrens301 Sent: Wednesday, September 02, 2009 9:38 PM To: Repeater-Builder@yahoogroups.com Subject: [Repeater-Builder] Re: Antenna SWR = Desense? Hi Eric, Hmmm, don't think I said above the station, but if I implied it, no, it's horizontal. I can look out the window see it! Nate - I only tried the 'ham quality' antenna because I knew it would be a better match than the DB224. It was easy to change, standing on a 6' ladder! Just wanted to see if a poor swr would induce the desense. There are no other communications systems within miles of my location, so who knows. Perhaps the metal building is the problem. A side question, dealing with separation. Obviously, when you are using a split site, vertical separation makes you a lot more $ than horizontal does. But, in this type of situation, where you are a single antenna with a duplexer, what real difference does vertical or horizontal separation from the station make? If I'm horizontal, could turn the whole system on it's side (including the antenna system), then it would be vertical. The straws that I'm grasping are getting smaller!! Thanks to all! Tim W5FN Yahoo! Groups Links
Re: [Repeater-Builder] Re: Antenna SWR = Desense?
On Sep 2, 2009, at 10:37 PM, tahrens301 wrote: Nate - I only tried the 'ham quality' antenna because I knew it would be a better match than the DB224. It was easy to change, standing on a 6' ladder! Just wanted to see if a poor swr would induce the desense. There are no other communications systems within miles of my location, so who knows. Perhaps the metal building is the problem. Got it now. I was somehow under the impression you were at a busy commercial site with other transmitters and things. Honestly it probably rules out some stuff if you're not. You didn't mention your frequencies. Another minor gotcha is always if you pick a frequency pair that just happens to have bad mathematical frequency relationships to your IF frequency, etc. Kevin has some interesting stories about the MASTR II and things he's found out about UHF ones over the years, regarding this... and there's been discussions in the past about high and low-side injection crystal frequencies when we move these ex-commercial repeaters designed for use higher or lower in the bands into the far reaches of the Amateur bands A side question, dealing with separation. Obviously, when you are using a split site, vertical separation makes you a lot more $ than horizontal does. But, in this type of situation, where you are a single antenna with a duplexer, what real difference does vertical or horizontal separation from the station make? If I'm horizontal, could turn the whole system on it's side (including the antenna system), then it would be vertical. Ahhh, you're missing what they're talking about. Vertical antennas push a majority of the signal toward the horizon, usually in a donut shaped pattern. When you're directly under or over a vertical antenna, the amount of signal you'll be illuminated with from that transmitter/antenna combo is much lower than when you're off to one side of it. In your case, what they're concerned about is shielding... if your receiver isn't shielded well, and your feedline isn't top-notch, since your repeater is 100' horizontally from your antenna, you're in your own transmitter's illumination pattern, and signals are stronger that you're trying to keep OUT of your receiver, than say if you were directly under your antenna in a box at the bottom of the tower. Anything leaks RF into your receiver... there's going to be more RF out to the sides of your antenna than there is to contend with directly underneath it. The straws that I'm grasping are getting smaller!! Here's a relatively simple test, and also not super expensive if you don't already have the gear... can you put a good quality 50-ohm dummy load up at the end of your feed line where the antenna is at, instead of the antenna temporarily. If you transmit into THAT and you have desense, something is leaking your TX BADLY back into your RX, and odds are it's in the building... not out on the tower. With only a dummy load out there to radiate, you'd eliminate RF getting back into your shack, just like a non-duplexed station might suffer from things being RF hot if you had a KW amplifier on HF and your antenna was only a few feet away (bad idea for RF exposure but just using it as an example) and without proper grounding, things like a CW key or an old Astatic microphone might bite you when TXing. If the desense goes away -- suspect the antenna or the feedline anywhere along the path. It would show that the RF from the antenna is getting Into something. If you're feeling overwhelmed, stop, take a break... new ideas come often when you're not actively thinking about the problem. Another good habit to get into is to write every test scenario down... if nothing else, you can hunt down other local repeater people, especially those with lots of experience like the commercial 2-way folks who are often also hams, and for a beverage and maybe the cost of lunch, they can look over what you've tried and offer suggestions... heck, maybe if you're lucky they can show up with fancy test gear you could NEVER get your hands on at a reasonable price in a million years. And of course, if you can get their EYEBALLS on it, the problem might become obvious. Example... a new repeater operator in this area is using some hardline that looks like it was whacked every 3 feet with a ball-peen hammer. His repeater works reasonably well, and I'm just bloody amazed it works AT ALL after seeing this junk hardline someone gave him that he knew in THEORY should be better than LMR 400 or the like... but in PRACTICE he didn't know what giant dents in hardline do to the stuff. That hardline is probably EATING all of his power before it ever reaches the radiator/antenna, and it probably looks like a WONDERFUL 1:1 match on a wattmeter. But return loss INCLUDES feedline losses, by definition... and it's a two-way thing if you're
RE: [Repeater-Builder] Re: Antenna SWR = Desense?
-snip- A side question, dealing with separation. Obviously, when you are using a split site, vertical separation makes you a lot more $ than horizontal does. But, in this type of situation, where you are a single antenna with a duplexer, what real difference does vertical or horizontal separation from the station make? If I'm horizontal, could turn the whole system on it's side (including the antenna system), then it would be vertical. Basically, if your receiver and your antenna are in line with each other, the antenna is shooting rf right at the receiver. If it was up above the receiver, the receiver would be under an umbrella safer from the rf being shot out at the horizon. Vertical antennas of course. I believe you've tried a dummy load at the antenna end of the feedline yes? Chris Kb0wlf The straws that I'm grasping are getting smaller!! Thanks to all! Tim W5FN
Re: [Repeater-Builder] Re: Antenna SWR = Desense?
At 9/2/2009 15:17, you wrote: The antenna is on the top of a small wooden storage building. A mast is placed up against the peak of the roof, and the 224 is on top of that. What's in the building? Any (loose, rusty) metal objects inside? Might also try a different antenna. Bob NO6B
RE: [Repeater-Builder] Re: Antenna SWR = Desense?
Tim, A high-gain antenna that is only 100 feet away horizontally is far too close. It is bathing your repeater equipment with RF, and very few machines can tolerate being in such a high RF field. Vertical versus horizontal separation is very roughly in a 1:45 ratio, that is, the isolation of 100 feet of vertical separation is roughly equivalent to about 4,500 feet of horizontal separation. In other words, your 100 feet of horizontal separation is no better than if you put a mag-mount whip right on the top of the repeater cabinet. You would likely have less desense if you mounted your DB224 antenna on the roof of your equipment shed, directly above the repeater, so that the repeater cabinet was in the shadow beneath the antenna. You might also consider filtering the DC power leads to prevent RF ingress through that path. 73, Eric Lemmon WB6FLY -Original Message- From: Repeater-Builder@yahoogroups.com [mailto:repeater-buil...@yahoogroups.com] On Behalf Of tahrens301 Sent: Wednesday, September 02, 2009 9:38 PM To: Repeater-Builder@yahoogroups.com Subject: [Repeater-Builder] Re: Antenna SWR = Desense? Hi Eric, Hmmm, don't think I said above the station, but if I implied it, no, it's horizontal. I can look out the window see it! Nate - I only tried the 'ham quality' antenna because I knew it would be a better match than the DB224. It was easy to change, standing on a 6' ladder! Just wanted to see if a poor swr would induce the desense. There are no other communications systems within miles of my location, so who knows. Perhaps the metal building is the problem. A side question, dealing with separation. Obviously, when you are using a split site, vertical separation makes you a lot more $ than horizontal does. But, in this type of situation, where you are a single antenna with a duplexer, what real difference does vertical or horizontal separation from the station make? If I'm horizontal, could turn the whole system on it's side (including the antenna system), then it would be vertical. The straws that I'm grasping are getting smaller!! Thanks to all! Tim W5FN
Re: [Repeater-Builder] Re: Antenna SWR = Desense?
look at all your repeater sheilding and interconnect cables from repeater dto duplexer and those cables. you appear to be getting signal ingress through the recieve side somehow. I have had antenna on top of the repeater using a mag mount and not had problems. Good luck this is a tough problem to resolve. Stan --- On Wed, 9/2/09, tahrens301 tahr...@swtexas.net wrote: From: tahrens301 tahr...@swtexas.net Subject: [Repeater-Builder] Re: Antenna SWR = Desense? To: Repeater-Builder@yahoogroups.com Date: Wednesday, September 2, 2009, 11:56 AM Hi All, And the winner is. Door # 2. Put the 2 meter vertical up on the stick at the end of the hard line, the desense was worse! Perfect match at the feed line end. Took dummy load put on far end of hard line no desense. Guess it is the proximity to the antenna. Although about 100', guess the RF is getting back into the box. Gonna set the antenna party for Friday morning. The stuff is going up on the tower (unless somebody can see some flaw in my logic can suggest another test)! Thanks again to all! Tim W5FN
Re: [Repeater-Builder] Re: Antenna SWR = Desense?
Tim Been there and done that! My guess is that you have corrosion in the antenna on top. The corrosion makes a good wide band rectifier of your transmit power and produces sufficient noise at your receive frequency to get back through your duplexer and into your receiver as desense. Actually, come to think about it, the end result of the situation is simular to bad LMR-400. Scott, N6NXI - Original Message - From: tahrens301 To: Repeater-Builder@yahoogroups.com Sent: Wednesday, September 02, 2009 9:56 AM Subject: [Repeater-Builder] Re: Antenna SWR = Desense? Hi All, And the winner is. Door # 2. Put the 2 meter vertical up on the stick at the end of the hard line, the desense was worse! Perfect match at the feed line end. Took dummy load put on far end of hard line no desense. Guess it is the proximity to the antenna. Although about 100', guess the RF is getting back into the box. Gonna set the antenna party for Friday morning. The stuff is going up on the tower (unless somebody can see some flaw in my logic can suggest another test)! Thanks again to all! Tim W5FN -- No virus found in this incoming message. Checked by AVG - www.avg.com Version: 8.5.409 / Virus Database: 270.13.75/2340 - Release Date: 09/01/09 20:03:00
Re: [Repeater-Builder] Re: Antenna SWR = Desense?
Tim--- I forgot that you spoke of 100' antenna separation. This suggests no duplexer and two feedlines. The meat of my story is still good---a corroded transmit antenna is capable of making and radiating allot of receive frequency noise ---even with between antenna pattern attenuation, there might well be enough to desense your receiver. Scott - Original Message - From: Scott Overstreet To: Repeater-Builder@yahoogroups.com Sent: Wednesday, September 02, 2009 1:24 PM Subject: Re: [Repeater-Builder] Re: Antenna SWR = Desense? Tim Been there and done that! My guess is that you have corrosion in the antenna on top. The corrosion makes a good wide band rectifier of your transmit power and produces sufficient noise at your receive frequency to get back through your duplexer and into your receiver as desense. Actually, come to think about it, the end result of the situation is simular to bad LMR-400. Scott, N6NXI - Original Message - From: tahrens301 To: Repeater-Builder@yahoogroups.com Sent: Wednesday, September 02, 2009 9:56 AM Subject: [Repeater-Builder] Re: Antenna SWR = Desense? Hi All, And the winner is. Door # 2. Put the 2 meter vertical up on the stick at the end of the hard line, the desense was worse! Perfect match at the feed line end. Took dummy load put on far end of hard line no desense. Guess it is the proximity to the antenna. Although about 100', guess the RF is getting back into the box. Gonna set the antenna party for Friday morning. The stuff is going up on the tower (unless somebody can see some flaw in my logic can suggest another test)! Thanks again to all! Tim W5FN No virus found in this incoming message. Checked by AVG - www.avg.com Version: 8.5.409 / Virus Database: 270.13.75/2340 - Release Date: 09/01/09 20:03:00 -- No virus found in this incoming message. Checked by AVG - www.avg.com Version: 8.5.409 / Virus Database: 270.13.76/2342 - Release Date: 09/02/09 18:03:00
RE: [Repeater-Builder] Re: Antenna SWR = Desense?
Why don't you raise the antenna, and get the repeater out of the RF field? To: Repeater-Builder@yahoogroups.com From: tahr...@swtexas.net Date: Wed, 2 Sep 2009 21:32:35 + Subject: [Repeater-Builder] Re: Antenna SWR = Desense? Hi Scott, The 100' of separation is from the repeater to where the antenna is located. I have a Telewave 6 cavity BpBr duplexer on the system. Single feed to one antenna. Thanks, Tim W5FN --- In Repeater-Builder@yahoogroups.com, Scott Overstreet sc...@... wrote: Tim--- I forgot that you spoke of 100' antenna separation. This suggests no duplexer and two feedlines. The meat of my story is still good---a corroded transmit antenna is capable of making and radiating allot of receive frequency noise ---even with between antenna pattern attenuation, there might well be enough to desense your receiver. Scott - Original Message - From: Scott Overstreet To: Repeater-Builder@yahoogroups.com Sent: Wednesday, September 02, 2009 1:24 PM Subject: Re: [Repeater-Builder] Re: Antenna SWR = Desense? Tim Been there and done that! My guess is that you have corrosion in the antenna on top. The corrosion makes a good wide band rectifier of your transmit power and produces sufficient noise at your receive frequency to get back through your duplexer and into your receiver as desense. Actually, come to think about it, the end result of the situation is simular to bad LMR-400. Scott, N6NXI - Original Message - From: tahrens301 To: Repeater-Builder@yahoogroups.com Sent: Wednesday, September 02, 2009 9:56 AM Subject: [Repeater-Builder] Re: Antenna SWR = Desense? Hi All, And the winner is. Door # 2. Put the 2 meter vertical up on the stick at the end of the hard line, the desense was worse! Perfect match at the feed line end. Took dummy load put on far end of hard line no desense. Guess it is the proximity to the antenna. Although about 100', guess the RF is getting back into the box. Gonna set the antenna party for Friday morning. The stuff is going up on the tower (unless somebody can see some flaw in my logic can suggest another test)! Thanks again to all! Tim W5FN -- No virus found in this incoming message. Checked by AVG - www.avg.com Version: 8.5.409 / Virus Database: 270.13.75/2340 - Release Date: 09/01/09 20:03:00 -- No virus found in this incoming message. Checked by AVG - www.avg.com Version: 8.5.409 / Virus Database: 270.13.76/2342 - Release Date: 09/02/09 18:03:00
Fw: Re: [Repeater-Builder] Re: Antenna SWR = Desense?
Does anybody use anything like Caig's DeOxit products? I'd treat each every connector in the system, inside outside the electronic cabinets, e.g. coax connectors. I find it works extremely well, indoors out. I've been using it for years. I have restored equipment rendered near-useless by bad switch contacts, connectors, even tube pins/sockets. Even an old Ford Tempo that could not be fixed--Caig'd every connector I could get to all its intermittent problems went away. Not really cheap but worth it to me. Lots of info at: www.caig.com PS I have NO commericial interest in Caig. --John WB0EQ --- On Wed, 9/2/09, Scott Overstreet sc...@becklawfirm.com wrote: From: Scott Overstreet sc...@becklawfirm.com Subject: Re: [Repeater-Builder] Re: Antenna SWR = Desense? To: Repeater-Builder@yahoogroups.com Date: Wednesday, September 2, 2009, 2:24 PM Tim Been there and done that! My guess is that you have corrosion in the antenna on top. The corrosion makes a good wide band rectifier of your transmit power and produces sufficient noise at your receive frequency to get back through your duplexer and into your receiver as desense. Actually, come to think about it, the end result of the situation is simular to bad LMR-400. Scott, N6NXI --
RE: [Repeater-Builder] Re: Antenna SWR = Desense?
Tim, I believe you stated in a previous message that the antenna was 100 feet away, horizontally. That is light years away from it being 100 feet ABOVE the repeater. 73, Eric Lemmon WB6FLY -Original Message- From: Repeater-Builder@yahoogroups.com [mailto:repeater-buil...@yahoogroups.com] On Behalf Of tahrens301 Sent: Wednesday, September 02, 2009 9:57 AM To: Repeater-Builder@yahoogroups.com Subject: [Repeater-Builder] Re: Antenna SWR = Desense? Hi All, And the winner is. Door # 2. Put the 2 meter vertical up on the stick at the end of the hard line, the desense was worse! Perfect match at the feed line end. Took dummy load put on far end of hard line no desense. Guess it is the proximity to the antenna. Although about 100', guess the RF is getting back into the box. Gonna set the antenna party for Friday morning. The stuff is going up on the tower (unless somebody can see some flaw in my logic can suggest another test)! Thanks again to all! Tim W5FN
Re: [Repeater-Builder] Re: Antenna SWR = Desense?
On Sep 2, 2009, at 3:16 PM, tahrens301 wrote: Don - I can put the iso-tee in line, feed the atten port into the spectrum analyzer. It should show me if the xmtr is having problems. However, the current antenna is a perfect match - no reflected power at all, so I think the xmtr 'should' be happy. Remember also... (just saying as a side-note, may not apply to THIS situation)... that a 50 ohm dummy load and hardline that doesn't radiate is also a perfect match. Sometimes you need to see if the antenna is REALLY radiating as it should be. (And this is difficult, but do-able.) If it looks like it doesn't perform as well as a similar or preferably the SAME antenna type at the SAME location, that's a great way to determine that there's something wrong and any such antenna is suspect from then on of horrible Passive IM mixes, or other site nastiness. You mentioned swapping in a ham quality antenna. It's a tempting troubleshooting technique, but if there are a bunch of transmitters on that site... don't leave it that way. All those joints on those floppy hunks of junk will EVENTUALLY bite either you, or more likely, someone else in the butt with a mix, as the antenna gets old and loose RF joints become little diodes... I'm still pretty sure you're fighting an external MIX of your own transmitter with something... in an active component of someone else's PA, in a rusty joint of that metal building, a loose/rusty bolt on the tower... and these things are a real PITA to find in a duplexed system, especially when you have nice gear like the DB antenna and good feedline and really WANT to assume everything's good, before you start ripping it apart, piece by piece... only to find that you've replaced EVERYTHING and the problem still exists. I'm tellin' ya... repeaters that have problems like this, WILL make you crazy. (This list is proof positive! GRIN!) :-) Or as a good friend puts it, Passive Intermod, the devil's snack food. -- Nate Duehr, WY0X n...@natetech.com facebook.com/denverpilot twitter.com/denverpilot
RE: [Repeater-Builder] Re: Antenna SWR = Desense?
Seems to me the three most-likely causes of your problem are: 1. Antenna itself is bad/noisy. Substituting antennas may help rule this out. 2. Not enough isolation between radiating antenna and equipment. The 100' of horizontal separation may not be enough to keep the strong RF out of your equipment, effectively bypassing/negating the isolation your finely-tuned duplexer is attempting to provide. 3. Mis-match due to out-of-band antenna is causing other problems, possibly even transmitter going spurious. While I generally don't recommend using isolators or Z-matchers as band-aids to cure antenna ills, using one to help rule this out as possible cause might be helpful as a short-term experiment. 4. You mention metal building, which conjures many bad memories of rooftop installations where all kinds of noise problems related to HVAC units, duct work, corrugated metal panels, metal screens/grills, ventilation stacks, cooling towers, etc. resulted in countless hours of time spent trying to reduce noise and passive intermod mixes. You're on your own on that one... --- Jeff WN3A -Original Message- From: Repeater-Builder@yahoogroups.com [mailto:repeater-buil...@yahoogroups.com] On Behalf Of tahrens301 Sent: Tuesday, September 01, 2009 4:03 PM To: Repeater-Builder@yahoogroups.com Subject: [Repeater-Builder] Re: Antenna SWR = Desense? Hi Joe, The repeater/duplexer is in my workshop (a large metal building). The heliax goes out the window to a smaller portable building about 100' away (horizontally spaced). The antenna is on that building about 10' off the ground. Don - took the dummyload analyzer to the end of the hard line, fed it into the iso-tee there. No desense is noted. Something's not right when the antenna gets hooked up. Maybe I should put up the ringo for a test. at least it's probably a bit better of a match. --- In Repeater-Builder@yahoogroups.com mailto:Repeater-Builder%40yahoogroups.com , Joe k1ike_m...@... wrote: You state DB-224 100' horizontally 10' vertically separated. I don't understand what you mean by that. Joe tahrens301 wrote: However, putting the system on the antenna (a 150-160 mhz DB-224 100' horizontally 10' vertically separated) through a metal building fed with 7/8 heliax, there seems to be no end to the desense! No virus found in this incoming message. Checked by AVG - www.avg.com Version: 8.5.409 / Virus Database: 270.13.65/2323 - Release Date: 09/01/09 06:52:00
Re: [Repeater-Builder] Re: Antenna SWR = Desense?
While you are out at the antenna, stick the wattmeter in line and check the foward/reflected there with the antenna and the dummy load. My guess is that you will quickly find your problem. I would check the connection to the DB-224 coax as well as the connections to each element. Also check the center connection. 30 foward and 3 reflected is a whole lot higher than I would accept; at least 10% of your RF out is being reflected. Milt N3LTQ - Original Message - From: tahrens301 tahr...@swtexas.net To: Repeater-Builder@yahoogroups.com Sent: Tuesday, September 01, 2009 4:02 PM Subject: [Repeater-Builder] Re: Antenna SWR = Desense? Hi Joe, The repeater/duplexer is in my workshop (a large metal building). The heliax goes out the window to a smaller portable building about 100' away (horizontally spaced). The antenna is on that building about 10' off the ground. Don - took the dummyload analyzer to the end of the hard line, fed it into the iso-tee there. No desense is noted. Something's not right when the antenna gets hooked up. Maybe I should put up the ringo for a test. at least it's probably a bit better of a match. --- In Repeater-Builder@yahoogroups.com, Joe k1ike_m...@... wrote: You state DB-224 100' horizontally 10' vertically separated. I don't understand what you mean by that. Joe tahrens301 wrote: However, putting the system on the antenna (a 150-160 mhz DB-224 100' horizontally 10' vertically separated) through a metal building fed with 7/8 heliax, there seems to be no end to the desense! Yahoo! Groups Links No virus found in this incoming message. Checked by AVG - www.avg.com Version: 8.5.392 / Virus Database: 270.13.73/2338 - Release Date: 08/31/09 17:52:00
RE: [Repeater-Builder] Re: Antenna SWR = Desense?
I swear to God, #4 will make you go completely insane. Best fixes... 1. Lower output power. The distance-squared rule is your friend if you're mixing somewhere EXTERNAL to your system. 2. Move off the site. LOL! I loved Jeff's very politically correct... You're on your own. on that one. Only if you've hunted and failed and hunted again and failed and hunted and failed, do you really get what he's saying there. :-) -- Nate Duehr n...@natetech.com On Tue, 01 Sep 2009 16:14 -0400, Jeff DePolo j...@broadsci.com wrote: Seems to me the three most-likely causes of your problem are: 1. Antenna itself is bad/noisy. Substituting antennas may help rule this out. 2. Not enough isolation between radiating antenna and equipment. The 100' of horizontal separation may not be enough to keep the strong RF out of your equipment, effectively bypassing/negating the isolation your finely-tuned duplexer is attempting to provide. 3. Mis-match due to out-of-band antenna is causing other problems, possibly even transmitter going spurious. While I generally don't recommend using isolators or Z-matchers as band-aids to cure antenna ills, using one to help rule this out as possible cause might be helpful as a short-term experiment. 4. You mention metal building, which conjures many bad memories of rooftop installations where all kinds of noise problems related to HVAC units, duct work, corrugated metal panels, metal screens/grills, ventilation stacks, cooling towers, etc. resulted in countless hours of time spent trying to reduce noise and passive intermod mixes. You're on your own on that one... --- Jeff WN3A -Original Message- From: [1]repeater-buil...@yahoogroups. com [mailto:[2]repeater-buil...@yahoogroups.com] On Behalf Of tahrens301 Sent: Tuesday, September 01, 2009 4:03 PM To: [3]repeater-buil...@yahoogroups.com Subject: [Repeater-Builder] Re: Antenna SWR = Desense? Hi Joe, The repeater/duplexer is in my workshop (a large metal building). The heliax goes out the window to a smaller portable building about 100' away (horizontally spaced). The antenna is on that building about 10' off the ground. Don - took the dummyload analyzer to the end of the hard line, fed it into the iso-tee there. No desense is noted. Something's not right when the antenna gets hooked up. Maybe I should put up the ringo for a test. at least it's probably a bit better of a match. --- In [4]repeater-buil...@yahoogroups.com mailto:Repeater-Builder%40yahoogroups.com , Joe k1ike_m...@... wrote: You state DB-224 100' horizontally 10' vertically separated. I don't understand what you mean by that. Joe tahrens301 wrote: However, putting the system on the antenna (a 150-160 mhz DB-224 100' horizontally 10' vertically separated) through a metal building fed with 7/8 heliax, there seems to be no end to the desense! No virus found in this incoming message. Checked by AVG - www.avg.com Version: 8.5.409 / Virus Database: 270.13.65/2323 - Release Date: 09/01/09 06:52:00 References 1. mailto:Repeater-Builder%40yahoogroups.com 2. mailto:Repeater-Builder%40yahoogroups.com 3. mailto:Repeater-Builder%40yahoogroups.com 4. mailto:Repeater-Builder%40yahoogroups.com 5. http://groups.yahoo.com/group/Repeater-Builder/message/93826;_ylc=X3oDMTM1czZha25kBF9TAzk3MzU5NzE0BGdycElkAzEwNDE2OARncnBzcElkAzE3MDUwNjMxMDgEbXNnSWQDOTM4MzAEc2VjA2Z0cgRzbGsDdnRwYwRzdGltZQMxMjUxODM2MDc5BHRwY0lkAzkzODI2 6. http://groups.yahoo.com/group/Repeater-Builder/post;_ylc=X3oDMTJwMm44YWZhBF9TAzk3MzU5NzE0BGdycElkAzEwNDE2OARncnBzcElkAzE3MDUwNjMxMDgEbXNnSWQDOTM4MzAEc2VjA2Z0cgRzbGsDcnBseQRzdGltZQMxMjUxODM2MDc5?act=replymessageNum=93830 7. http://groups.yahoo.com/group/Repeater-Builder/post;_ylc=X3oDMTJkam90ZThzBF9TAzk3MzU5NzE0BGdycElkAzEwNDE2OARncnBzcElkAzE3MDUwNjMxMDgEc2VjA2Z0cgRzbGsDbnRwYwRzdGltZQMxMjUxODM2MDc5 8. http://groups.yahoo.com/group/Repeater-Builder/messages;_ylc=X3oDMTJkZnA4dms4BF9TAzk3MzU5NzE0BGdycElkAzEwNDE2OARncnBzcElkAzE3MDUwNjMxMDgEc2VjA2Z0cgRzbGsDbXNncwRzdGltZQMxMjUxODM2MDc5 9. http://groups.yahoo.com/group/Repeater-Builder/files;_ylc=X3oDMTJlbmtxam11BF9TAzk3MzU5NzE0BGdycElkAzEwNDE2OARncnBzcElkAzE3MDUwNjMxMDgEc2VjA2Z0cgRzbGsDZmlsZXMEc3RpbWUDMTI1MTgzNjA3OQ-- 10. http://groups.yahoo.com/group/Repeater-Builder/photos;_ylc=X3oDMTJkcm8zMGdjBF9TAzk3MzU5NzE0BGdycElkAzEwNDE2OARncnBzcElkAzE3MDUwNjMxMDgEc2VjA2Z0cgRzbGsDcGhvdARzdGltZQMxMjUxODM2MDc5 11. http://groups.yahoo.com/group/Repeater-Builder/links;_ylc=X3oDMTJlNDFsdGE4BF9TAzk3MzU5NzE0BGdycElkAzEwNDE2OARncnBzcElkAzE3MDUwNjMxMDgEc2VjA2Z0cgRzbGsDbGlua3MEc3RpbWUDMTI1MTgzNjA3OQ-- 12. http://groups.yahoo.com/group/Repeater-Builder/members;_ylc=X3oDMTJkZnV2NDRsBF9TAzk3MzU5NzE0BGdycElkAzEwNDE2OARncnBzcElkAzE3MDUwNjMxMDgEc2VjA2Z0cgRzbGsDbWJycwRzdGltZQMxMjUxODM2MDc5 13. http://groups.yahoo.com/;_ylc=X3oDMTJjNGJqdjI4BF9TAzk3MzU5NzE0BGdycElkAzEwNDE2OARncnBzcElkAzE3MDUwNjMxMDgEc2VjA2Z0cgRzbGsDZ2ZwBHN0aW1lAzEyNTE4MzYwNzk- 14.
Re: [Repeater-Builder] Re: Antenna SWR = Desense?
--- On Tue, 9/1/09, tahrens301 tahr...@swtexas.net wrote: From: tahrens301 tahr...@swtexas.net Subject: [Repeater-Builder] Re: Antenna SWR = Desense? To: Repeater-Builder@yahoogroups.com Date: Tuesday, September 1, 2009, 5:29 PM Hi Jeff, I'll try a different antenna... perhaps that's it. Horizontal isolation possibly not enough, but 'only' running 30 watts out, the repeater is a quantar, all leads are RG214, so didn't figure that would be it... I've seen a lot of installations with antennas pretty close to the system. Is that 214 double shielded ? I have seen some marked 214 that was not double shielded. Also you almost have a 2:1 swr. Seems way too high to me.
RE: [Repeater-Builder] Re: Antenna SWR = Desense?
Numbers 1 or 4 are the more likely. He has a Quantar which is designed to live in high RF environments at antenna sites making #2 unlikely. Also, with respect to #3, the Quantar PA has a built in circulator as standard equipment. OK. I missed (or maybe wasn't paying attention) that he had a Quantar. Still, the high VSWR isn't something I'd want to live with, especially when connected to a duplexer. I worked on an MSR2000 installed in the upper level of a two-story mechanical room (concrete) that suffered desense from its own antenna (DB224) which was mounted to the exterior of wall, maybe 15' directly above the repeater cabinet (whoever installed it probably chose that mounting location figuring it was the shortest cable path). Moving the antenna to the other side of the penthouse to get another 50 feet or so of distance from the repeater reduced the desense substantially, but didn't completely eliminate it. Moving the repeater to the lower level did the trick. So I wouldn't totally rule out #2 just yet, although given the equipment complement, I agree that #1 and #4 or other external factors are more likely (and an MSR2000 ain't no Quantar by any stretch of the imagination). --- Jeff --- In Repeater-Builder@yahoogroups.com mailto:Repeater-Builder%40yahoogroups.com , Jeff DePolo j...@... wrote: Seems to me the three most-likely causes of your problem are: 1. Antenna itself is bad/noisy. Substituting antennas may help rule this out. 2. Not enough isolation between radiating antenna and equipment. The 100' of horizontal separation may not be enough to keep the strong RF out of your equipment, effectively bypassing/negating the isolation your finely-tuned duplexer is attempting to provide. 3. Mis-match due to out-of-band antenna is causing other problems, possibly even transmitter going spurious. While I generally don't recommend using isolators or Z-matchers as band-aids to cure antenna ills, using one to help rule this out as possible cause might be helpful as a short-term experiment. 4. You mention metal building, which conjures many bad memories of rooftop installations where all kinds of noise problems related to HVAC units, duct work, corrugated metal panels, metal screens/grills, ventilation stacks, cooling towers, etc. resulted in countless hours of time spent trying to reduce noise and passive intermod mixes. You're on your own on that one... No virus found in this incoming message. Checked by AVG - www.avg.com Version: 8.5.409 / Virus Database: 270.13.65/2323 - Release Date: 09/01/09 06:52:00
Re: [Repeater-Builder] Re: Antenna SWR = Desense?
Tim, This might be it. I miss read the previous. Try the Ringo for grins and see what transpires. Might be a bad connection on the old antenna. BR -Richard From: tahrens301 tahr...@swtexas.net To: Repeater-Builder@yahoogroups.com Sent: Tuesday, September 1, 2009 4:02:35 PM Subject: [Repeater-Builder] Re: Antenna SWR = Desense? Hi Joe, The repeater/duplexer is in my workshop (a large metal building). The heliax goes out the window to a smaller portable building about 100' away (horizontally spaced). The antenna is on that building about 10' off the ground. Don - took the dummyload analyzer to the end of the hard line, fed it into the iso-tee there. No desense is noted. Something's not right when the antenna gets hooked up. Maybe I should put up the ringo for a test. at least it's probably a bit better of a match. --- In Repeater-Builder@ yahoogroups. com, Joe k1ike_mail@ ... wrote: You state DB-224 100' horizontally 10' vertically separated. I don't understand what you mean by that. Joe tahrens301 wrote: However, putting the system on the antenna (a 150-160 mhz DB-224 100' horizontally 10' vertically separated) through a metal building fed with 7/8 heliax, there seems to be no end to the desense!
