Testing and tuning mobile antennas
I'm stumped on a problem I've been having with a Comet UHV-4 quad band
antenna (10m/6m/2m/70cm). It's mounted to a Comet CP-5M mobile mount on my Saturn SL1. The problem I have is that I cannot get it to tune. I figure that it's an insufficient RF ground. I've tried running braid from a good ground location in the trunk to the mount (good metal to metal contact on the "car" end of the braid). Still nothing. So I was wondering if there would be a way to tune the antenna off the car. I was thinking of creating a ground plane with several 1/4 wavelength wires on each of the bands, and then adjusting the antenna to bring it into tune. That way I would know if the ground braid I put into the car is working well enough. Does this make sense? Or is it a wasted effort, and I should spend my time on improving the ground in the car? What would you do? 73, Patrick N3EO |
all that tuning it off the car would prove is that it could be tuned... that
is, that it was working electrically and the adjustments were possible. unless you were very lucky the tuning on the car would be different than any off car rig you set up. i don't know about the saturn's construction, but if its mostly plastic there may not be enough metal close to the antenna to work properly. most mobile antennas are designed to be attached to a reasonably large piece of sheet metal, having a thin braid or just frame pieces as the ground plane would likely make the tuning much different than it was designed for. if where it is mounted is plastic you may want to try running several radials connected to the mounting bracket and just taped inside the trunk lid or fender... of if you can do it stick a piece of aluminum flashing inside attached to the bracket... the more metal the better most likely. "Patrick Gardella" wrote in message om... I'm stumped on a problem I've been having with a Comet UHV-4 quad band antenna (10m/6m/2m/70cm). It's mounted to a Comet CP-5M mobile mount on my Saturn SL1. The problem I have is that I cannot get it to tune. I figure that it's an insufficient RF ground. I've tried running braid from a good ground location in the trunk to the mount (good metal to metal contact on the "car" end of the braid). Still nothing. So I was wondering if there would be a way to tune the antenna off the car. I was thinking of creating a ground plane with several 1/4 wavelength wires on each of the bands, and then adjusting the antenna to bring it into tune. That way I would know if the ground braid I put into the car is working well enough. Does this make sense? Or is it a wasted effort, and I should spend my time on improving the ground in the car? What would you do? 73, Patrick N3EO |
I used to run mobile in a SL-1 using Hamsticks and the Hustler mobile
antennas. Where and how did you mount the antenna? I used a lip mount on the trunk hood [which is metal] and three different ground straps from the trunk hood to various points on the frame. Deacon Dave, W1MCE Patrick Gardella wrote: I'm stumped on a problem I've been having with a Comet UHV-4 quad band antenna (10m/6m/2m/70cm). It's mounted to a Comet CP-5M mobile mount on my Saturn SL1. The problem I have is that I cannot get it to tune. I figure that it's an insufficient RF ground. I've tried running braid from a good ground location in the trunk to the mount (good metal to metal contact on the "car" end of the braid). Still nothing. So I was wondering if there would be a way to tune the antenna off the car. I was thinking of creating a ground plane with several 1/4 wavelength wires on each of the bands, and then adjusting the antenna to bring it into tune. That way I would know if the ground braid I put into the car is working well enough. Does this make sense? Or is it a wasted effort, and I should spend my time on improving the ground in the car? What would you do? 73, Patrick N3EO |
On 24 Mar 2004 14:12:07 -0800, Patrick Gardella wrote:
I'm stumped on a problem I've been having with a Comet UHV-4 quad band antenna (10m/6m/2m/70cm). It's mounted to a Comet CP-5M mobile mount on my Saturn SL1. The problem I have is that I cannot get it to tune. I figure that it's an insufficient RF ground. I've tried running braid from a good ground location in the trunk to the mount (good metal to metal contact on the "car" end of the braid). Still nothing. Those Saturn's are plastic panelled aren't they? There is 80% of your answer right there! If I were you I would try to run a thick braid directly to the car FRAME from your antenna ground point, as there is probably little real metal in that trunk. The frame would connect all large pieces of metal in your car to your antenna ground. I would also do the same at the rig end, directly to the engine block and firewall panel. So I was wondering if there would be a way to tune the antenna off the car. I was thinking of creating a ground plane with several 1/4 wavelength wires on each of the bands, and then adjusting the antenna to bring it into tune. That way I would know if the ground braid I put into the car is working well enough. Tuning the antenna away from the car would only prove that the antenna is tuneable, in the very unlikely chance there is something wrong with it. That I doubt very much. Patrick, I'm afraid that with that car, despite doing the above, that you might never get as good a ground or signal as someone with a metal panelled car. But then I have heard some good signals from mobile antennas mounted to fiberglass recreational vehicles, so you never know! Good luck with your efforts. Larry Gagnon VE7EA ******************************** to reply via email remove "fake" |
Patrick, Sorry, tuning the antenna 'off of' the car won't work (miracles do happen, but don't count on it). The most likely problem is as you thought, a not so good 'ground', but maybe not. Does anything you do change the tuning of the antenna at all? Maybe not get it to where you want it (freq.), but does change it's resonant freq? If not, then there's something else 'going on' besides the inadequate grounding/counterpoise. Make sure you have a good connection through the mount, no shorts/opens except as they should be, etc. And you probably should do something about the grounding/counterpoise, maybe clip a wire to the base of the mount as a counterpoise to see what difference it makes (just lay it on the surface of the car for now). The length of the counterpoise isn't that critical, but too long is 'better' than too short. Changing the location of the mount is also something you might try. Good luck... 'Doc |
"'Doc" wrote in message ... Patrick, Sorry, tuning the antenna 'off of' the car won't work (miracles do happen, but don't count on it). The most likely problem is as you thought, a not so good 'ground', but maybe not. Does anything you do change the tuning of the antenna at all? Maybe not get it to where you want it (freq.), but does change it's resonant freq? If not, then there's something else 'going on' besides the inadequate grounding/counterpoise. Make sure you have a good connection through the mount, no shorts/opens except as they should be, etc. And you probably should do something about the grounding/counterpoise, maybe clip a wire to the base of the mount as a counterpoise to see what difference it makes (just lay it on the surface of the car for now). The length of the counterpoise isn't that critical, but too long is 'better' than too short. Changing the location of the mount is also something you might try. Good luck... 'Doc |
Perhaps I should enter the text BEFORE hitting the send button, eh?
Doc has a good idea here with an "external" ground/counterpoise ae a test. However, I would ask: How are you determining when it is tuned? What are you using to determine if it is tuned? I don't think this talk about connecting braid to the FRAME is good. The antennas are usually designed to have a ground-plane right at the base of the antenna and a length of braid can be easily more than a quarter wave at 2M and 440 and the frame is far from the antenna base. With plastic paneled cars it is common to put some sort of foil or plate inside the body to provide the ground plane. -- Steve N, K,9;d, c. i My email has no u's. "Steve Nosko" wrote in message ... "'Doc" wrote in message ... Patrick, Sorry, tuning the antenna 'off of' the car won't work (miracles do happen, but don't count on it). The most likely problem is as you thought, a not so good 'ground', but maybe not. Does anything you do change the tuning of the antenna at all? Maybe not get it to where you want it (freq.), but does change it's resonant freq? If not, then there's something else 'going on' besides the inadequate grounding/counterpoise. Make sure you have a good connection through the mount, no shorts/opens except as they should be, etc. And you probably should do something about the grounding/counterpoise, maybe clip a wire to the base of the mount as a counterpoise to see what difference it makes (just lay it on the surface of the car for now). The length of the counterpoise isn't that critical, but too long is 'better' than too short. Changing the location of the mount is also something you might try. Good luck... 'Doc |
Thanks, Dave. The mount is on the trunk lip. I've got the
grounding strap running from the mount set screws to the frame of the car. So you basically ensured that the trunk lid had good contact with the rest of the car? 73, Patrick N3EO Dave Shrader wrote in message news:K1p8c.1594$w54.9895@attbi_s01... I used to run mobile in a SL-1 using Hamsticks and the Hustler mobile antennas. Where and how did you mount the antenna? I used a lip mount on the trunk hood [which is metal] and three different ground straps from the trunk hood to various points on the frame. Deacon Dave, W1MCE Patrick Gardella wrote: I'm stumped on a problem I've been having with a Comet UHV-4 quad band antenna (10m/6m/2m/70cm). It's mounted to a Comet CP-5M mobile mount on my Saturn SL1. The problem I have is that I cannot get it to tune. I figure that it's an insufficient RF ground. I've tried running braid from a good ground location in the trunk to the mount (good metal to metal contact on the "car" end of the braid). Still nothing. So I was wondering if there would be a way to tune the antenna off the car. I was thinking of creating a ground plane with several 1/4 wavelength wires on each of the bands, and then adjusting the antenna to bring it into tune. That way I would know if the ground braid I put into the car is working well enough. Does this make sense? Or is it a wasted effort, and I should spend my time on improving the ground in the car? What would you do? 73, Patrick N3EO |
Thanks, Doc.
I don't have an antenna analyzer, so I can't check the resonant freq that way. I was relying on an SWR meter (my shack one). Nothing at all changes when I adjust the antenna. SWR doesn't move. I may try to borrow an analyzer from someone to check that out. The mount and cable are fine. Just got a new 2m/70cm dual band antenna to use until I can get the UHV-4 working. It has a nice SWR of around 1.3 on 2m. On the UHV-4 antenna, I can't get below an SWR on 2m of around 5 or 6, even though it's supposed to be ground independant (1/2 wavelength). I can't adjust the 2m/70cm at all anyway. It's fixed. So as you said, there may be something else wrong with the antenna itself. I may just ship it back to Comet to see what they can find out. That high an SWR is just wrong on 2m. But I may try the counterpoise initially, just to find out. 73, Patrick N3EO 'Doc wrote in message ... Patrick, Sorry, tuning the antenna 'off of' the car won't work (miracles do happen, but don't count on it). The most likely problem is as you thought, a not so good 'ground', but maybe not. Does anything you do change the tuning of the antenna at all? Maybe not get it to where you want it (freq.), but does change it's resonant freq? If not, then there's something else 'going on' besides the inadequate grounding/counterpoise. Make sure you have a good connection through the mount, no shorts/opens except as they should be, etc. And you probably should do something about the grounding/counterpoise, maybe clip a wire to the base of the mount as a counterpoise to see what difference it makes (just lay it on the surface of the car for now). The length of the counterpoise isn't that critical, but too long is 'better' than too short. Changing the location of the mount is also something you might try. Good luck... 'Doc |
Patrick Gardella wrote:
Thanks, Dave. The mount is on the trunk lip. I've got the grounding strap running from the mount set screws to the frame of the car. I ran three different ground strap, 1.5 inches wide, from the trunk lip/lid to the car frame. First, I burnished the finish off the lip right under the antenna mount. I added a strap from that point to the nearest point of metal connected to the frame at the wheel well. Next I loosened the two trunks lip supports, hinges, and burnished the finish off under them. A strap was connected from one mount to the metal that houses the Saturn's speakers [rear deck]. The second strap was fastened to a burnished surface under the latch for the trunk mount. All burnished surface/strap locations were weather sealed with "Coax Seal" from HRO. Note: the radio, IC706 MKIIg, was bolted to the rear deck between the speakers and the remote head was installed at the drivers seat. The bolt locations were burnished to bare metal. So you basically ensured that the trunk lid had good contact with the rest of the car? 73, Patrick N3EO Dave Shrader wrote in message news:K1p8c.1594$w54.9895@attbi_s01... I used to run mobile in a SL-1 using Hamsticks and the Hustler mobile antennas. Where and how did you mount the antenna? I used a lip mount on the trunk hood [which is metal] and three different ground straps from the trunk hood to various points on the frame. Deacon Dave, W1MCE Patrick Gardella wrote: I'm stumped on a problem I've been having with a Comet UHV-4 quad band antenna (10m/6m/2m/70cm). It's mounted to a Comet CP-5M mobile mount on my Saturn SL1. The problem I have is that I cannot get it to tune. I figure that it's an insufficient RF ground. I've tried running braid from a good ground location in the trunk to the mount (good metal to metal contact on the "car" end of the braid). Still nothing. So I was wondering if there would be a way to tune the antenna off the car. I was thinking of creating a ground plane with several 1/4 wavelength wires on each of the bands, and then adjusting the antenna to bring it into tune. That way I would know if the ground braid I put into the car is working well enough. Does this make sense? Or is it a wasted effort, and I should spend my time on improving the ground in the car? What would you do? 73, Patrick N3EO |
I am trying to get an SWR that will actually read on my SWR meter. :) Right
now it's off the scale on 10m and 6m. It's around 5 or 6 on 2m. I don't have a meter for 70cm. FWIW this antenna is a quad band: 10m/6m/2m/70cm . My dual band (2m/70cm) works just fine. Patrick "Steve Nosko" wrote in message ... Perhaps I should enter the text BEFORE hitting the send button, eh? Doc has a good idea here with an "external" ground/counterpoise ae a test. However, I would ask: How are you determining when it is tuned? What are you using to determine if it is tuned? I don't think this talk about connecting braid to the FRAME is good. The antennas are usually designed to have a ground-plane right at the base of the antenna and a length of braid can be easily more than a quarter wave at 2M and 440 and the frame is far from the antenna base. With plastic paneled cars it is common to put some sort of foil or plate inside the body to provide the ground plane. -- Steve N, K,9;d, c. i My email has no u's. "Steve Nosko" wrote in message ... "'Doc" wrote in message ... Patrick, Sorry, tuning the antenna 'off of' the car won't work (miracles do happen, but don't count on it). The most likely problem is as you thought, a not so good 'ground', but maybe not. Does anything you do change the tuning of the antenna at all? Maybe not get it to where you want it (freq.), but does change it's resonant freq? If not, then there's something else 'going on' besides the inadequate grounding/counterpoise. Make sure you have a good connection through the mount, no shorts/opens except as they should be, etc. And you probably should do something about the grounding/counterpoise, maybe clip a wire to the base of the mount as a counterpoise to see what difference it makes (just lay it on the surface of the car for now). The length of the counterpoise isn't that critical, but too long is 'better' than too short. Changing the location of the mount is also something you might try. Good luck... 'Doc |
"Patrick Gardella" wrote in message om... Thanks, Doc. I don't have an antenna analyzer, so I can't check the resonant freq that way. I was relying on an SWR meter (my shack one). Nothing at all changes when I adjust the antenna. SWR doesn't move. I may try to borrow an analyzer from someone to check that out. The mount and cable are fine. Just got a new 2m/70cm dual band antenna to use until I can get the UHV-4 working. It has a nice SWR of around 1.3 on 2m. On the UHV-4 antenna, I can't get below an SWR on 2m of around 5 or 6, even though it's supposed to be ground independant (1/2 wavelength). I can't adjust the 2m/70cm at all anyway. It's fixed. Verify that the screw-off connector (NMO or 259) is actually making contact... what you're describing (super high swr on HF, high swr on 2m) points to a piece of unterminated coax with no antenna on the end! Try reading swr without the UHV4 connected... same reading? Bad connection... __ Steve KI5YG .. |
There is a reason why people post on usenet. They get answers.
And Steve, you have solved a years worth of puzzling and tweaking. The SWR was the same with or without an antenna. The antenna is bad. From the PL259 to the antenna I get no connectivity. I just tested it with a VOM. Why is it that the simple things are the last things you check. Now does anyone know how to take a UHV-4 apart? ;) 73, Patrick N3EO " Stephen Cowell" wrote in message . com... "Patrick Gardella" wrote in message om... Thanks, Doc. I don't have an antenna analyzer, so I can't check the resonant freq that way. I was relying on an SWR meter (my shack one). Nothing at all changes when I adjust the antenna. SWR doesn't move. I may try to borrow an analyzer from someone to check that out. The mount and cable are fine. Just got a new 2m/70cm dual band antenna to use until I can get the UHV-4 working. It has a nice SWR of around 1.3 on 2m. On the UHV-4 antenna, I can't get below an SWR on 2m of around 5 or 6, even though it's supposed to be ground independant (1/2 wavelength). I can't adjust the 2m/70cm at all anyway. It's fixed. Verify that the screw-off connector (NMO or 259) is actually making contact... what you're describing (super high swr on HF, high swr on 2m) points to a piece of unterminated coax with no antenna on the end! Try reading swr without the UHV4 connected... same reading? Bad connection... __ Steve KI5YG . |
Patrick Gardella wrote:
There is a reason why people post on usenet. They get answers. SNIP Why is it that the simple things are the last things you check. SNIP ... Wrong comment!! The Problem item is ALWAYS the last thing you check!!! I've retired from engineering which included a four year sojourn into professional photography. My medium format camera is/was defective. I check and replaced the battery that runs the shutter. Still defective so off to the repair shop. I received a call from the repair shop yesterday, Friday, describing the defect and requesting approval to repair. ???Are you ready??? The replacement battery was defective!!!! I'm red faced!! I'm also $85 poorer for the want of a $3 lithium battery :-) or :-( Moral[s] to the story: It's always the last thing ... It's always the simplest thing ... It's always the most embarassing thing ... etc. W1MCE |
Dave Shrader wrote:
Moral[s] to the story: It's always the last thing ... It's a no-brainer, Dave. When one diagnoses the problem, one stops looking. One would be stupid to continue after the "last thing". :-) -- 73, Cecil http://www.qsl.net/w5dxp -----= Posted via Newsfeeds.Com, Uncensored Usenet News =----- http://www.newsfeeds.com - The #1 Newsgroup Service in the World! -----== Over 100,000 Newsgroups - 19 Different Servers! =----- |
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"Richard Clark" wrote in message ... On 27 Mar 2004 14:23:33 -0800, (Patrick Gardella) wrote: Now does anyone know how to take a UHV-4 apart? ;) Hi Patrick, Before you do that (what would you fix?); confirm your reading with a load in its place (terminate the connection). Glad to hear my psychic powers are still up to snuff... :) But make sure that the connection is working before you take the antenna apart... you may be able to bend a spring (NMO) or tweak some contact leaves (259) and get the thing working right! Sometimes connectors have thread problems that prevent them from bottoming properly when screwed on.... check all these things. Make sure there's no little piece of plastic over the important bits, stuff like that. Check for a broken center conductor... trunk lip mounts have been known to do this to coax, and the bigger antenna may be pulling the connection apart. __ Steve KI5YG .. |
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