2002 Crown Victoria SWR issues

[btrains]

I am trying to install a low band Syntor X9000 in my Crown Victoria. I have followed the directions to diplex a 10 meter and 6 meter antenna to get dual ham band coverage. The problem I have is terrible SWR. To keep the antennas as far from each other as possible, I have used trunk lip NMO mounts. This also made cutting and installing much easier. The problem is that individual SWRs on those mounts are 5:1 on 50 MHz and ∞ on 29 MHz. I have a drilled out NMO mounted in the center of the trunk lid. On 50 MHz, this mount gives me 1.5:1 or better, and 4-5:1 on 29 MHz. I have followed the cutting guides from Larsen for these whips, and I have tested my 29 MHz whip on a different vehicle with a different radio. This whip has 1.1:1 at 29.600 MHz.

I took a magnetic mount and placed it in various locations on my trunk, and got 1.5:1 or better when the magnet mount was placed next to the NMO mount in the center of the trunk. The rest of the trunk had terrible SWR.

What can I do to improve my SWR on these lip mounts? I don't know what else to do to try and improve my SWR. The center NMO mount can be used for 50 MHz since i know I can get good SWR on that. I'll have to cut the coax to the proper diplex length however. But I don't have an area in which I can put the 29 MHz whip without terrible SWR.

[Jim202]

I am trying to install a low band Syntor X9000 in my Crown Victoria. I have followed the directions to diplex a 10 meter and 6 meter antenna to get dual ham band coverage. The problem I have is terrible SWR. To keep the antennas as far from each other as possible, I have used trunk lip NMO mounts. This also made cutting and installing much easier. The problem is that individual SWRs on those mounts are 5:1 on 50 MHz and ∞ on 29 MHz. I have a drilled out NMO mounted in the center of the trunk lid. On 50 MHz, this mount gives me 1.5:1 or better, and 4-5:1 on 29 MHz. I have followed the cutting guides from Larsen for these whips, and I have tested my 29 MHz whip on a different vehicle with a different radio. This whip has 1.1:1 at 29.600 MHz.

I took a magnetic mount and placed it in various locations on my trunk, and got 1.5:1 or better when the magnet mount was placed next to the NMO mount in the center of the trunk. The rest of the trunk had terrible SWR.

What can I do to improve my SWR on these lip mounts? I don't know what else to do to try and improve my SWR. The center NMO mount can be used for 50 MHz since i know I can get good SWR on that. I'll have to cut the coax to the proper diplex length however. But I don't have an area in which I can put the 29 MHz whip without terrible SWR.

Have you tried running some ground straps from the trunk lid to the body. The trunks are generally poorly grounded and tend to be a floating piece of metal at any of the lower frequencies. Use some wide copper braid. Like take a piece of RG8 and slice off the outer jacket. then slide the shielding off. Flatten it out and you have some flat copper braid. On the ends where your going to attach it to the trunk lid and body, make a hole for the grounding bolt. Then tin the area with solder. This will make for a better connection and will last longer.

On the antennas, remember that you need to pay attention to coax cable length. The 6 meter antenna cable wants to be the correct length for 10 meters. The 10 meter antenna coax cable wants to be the length of the 6 meter frequency. Once you get the antennas tuned up correctly, then put the T connector at the radio and attach both coax cables. You should be good to go.

Jim

[btrains]

Jim, I've replaced both ground straps from the trunk lid to the frame with flat, roughly one inch wide braid. I have used my multi meter to test conductivity between the ground portion of the NMO mounts both on the lip mounts and the center drilled mount, and the ground straps I installed. The conductivity is very good, typically measuring around 1 or so on my meter. I usually use the "sound" setting because the leads are not the longest, so I don't exactly know what scale of Ohms that selection uses...

Its been a while since I cut the coax cables for 6 and 10 meters, however I do remember having to ballpark a small amount since the Motorola chart doesn't go down to 29 or up to 54. Maybe the coax connectors have some issue, as I used solder connectors designed for relatively thick coax, and my lip mounts have standard RG-58.

Then again, that wouldn't explain why the only location that has good SWR, even on a mag mount, is the center of the trunk... I might just have to carry a mag mount and the 10 meter whip in the trunk. Would be the easiest solution...

[Jim202]

OK, found what I was looking for. Here is the document on making the dual antenna setup for the Syntor X9000 low band operation. The chart doesn't go into the ham 10 and 6 meter bands, but you should be able to figure it out from the information given.

http://www.repeater-builder.com/antenna ... ntenna.pdf


Jim

[Tom in D.C.]

FWIW, if you're putting RG-58 on a standard PL259 connector you need the UG-175 screw-in reducer. For RG-8X and RG-59 you need the UG-176 reducer. Thin coax into a PL259 without using the screw-in reducer is definitely not a good idea, especially in mobile installations.

[Astro Spectra]

Going back to your original issues it's clear there is something wrong with the 10m whip. Obvious questions do you have the right base and are you testing outside? If the whip section is the right length and the MNO mount is installed correctly on the centre of the trunk then there's not much that can go wrong. Can you try a second base? There's a chance that the loading coil inside is for another low band split or is just faulty.

[Jim202]

Forgot to ask just what coil your using under the whip. The NMO27 is what you should be using for 10 meters. Follow the cutting chart that comes with the coil.

Jim

[Astro Spectra]

For the NMO27 see: http://productfinder.pulseeng.com/produ ... /NMO27.pdf

[Astro Spectra]

Fixed URL in last post.

By the way just reading the Larsen cutting instructions (Revision 4/97) and noticed the statement "Under some conditions, low band antennas (27 to 54 MHz) on a trunk lid can result in an undesirable resonance with excessively high VSWR at some frequencies."

[btrains]

Sorry for not getting back to this post until now, to answer the question about the 10 meter whip, it is a Larsen NMO27 base. Using the cutting chart shown, I trimmed the antenna for 29.600 MHz including spring. I tested this whip on a magnetic mount on a different vehicle using a Radio Shack HTX-10 10 meter radio. The SWR was below 1.2:1 at 29.600 MHz. Using a magnetic mount on the center of the Crown Vic trunk, I was able to achieve 1.5 SWR. Using the drilled NMO mount in the center of the trunk that I had placed this mag mount next to, I was getting 3 or even 4 SWR. Obviously I did not keep the mag mount sitting on the trunk while testing the center drilled NMO mount.

I have tried affixing the mag mount to other locations on the roof of the car, with poor results.

I purchased new Larsen trunk lip mounts (the previous ones I tried using were Pro-Am) and am in the process of cutting the coax for each to the proper length in the diplex chart. I have not installed either on the vehicle yet. I hope these higher quality mounts help with the SWR issue, because otherwise I will just have to stick with a 6 meter whip in the center NMO mount, and carry the 10 meter whip on a mag mount in the trunk, and remove the 6 meter whip and put the mag mount in the center of the trunk to work 10 meters! I guess it wouldn't be that much of an issue, but ideally I'd like to get the whole T-connector set up working.

[Wowbagger]

Silly question: do you know that the trunk lip mount is good? Have you tried putting a different antenna on it and checking the VSWR? It could be the mount has a problem (e.g. a whisker between the center and ground) and that is causing your problems.

[Bill_G]

Silly question: do you know that the trunk lip mount is good? Have you tried putting a different antenna on it and checking the VSWR? It could be the mount has a problem (e.g. a whisker between the center and ground) and that is causing your problems.

My question is along the same lines as wow's.

If the same whip / base load were used during testing with a mag mount, then they are not what is causing this huge increase in vswr. It's the new cable / mount / connector.

[Jim202]

Maybe it's time to break out the Ohm meter and see if you have a short between the center conductor and the shield. If that is good, then check the continuity from the coax connector center conductor and the center of the NMO mount. Don't forget to check the continuity from the PL-259 shell to the ground ring on the NMO mount.

By any chance are you using the correct reducer to fit the PL-259 connector on the radio end? If so, has the coax cable shield been soldered to the reducer? Have seen many a coax connector installed with the RG-58 shield not soldered to the reducer.

There are silver plated connectors. There are tin plated connectors. Both do not solder the same. I always scrape off or file off the tin plating where I am going to solder to. Makes the soldering that much easier and you don't end up melting the coax cable in the process.

Jim

[Birken Vogt]

Any resolution? I was thinking of trying this myself someday.

[btrains]

I have just returned from my trip. Have not finished installing the new trunk lip mounts yet. Weather permitting I will finish that in the next day or two.

To answer some other questions: I have already used my Ohm meter to test both the center contact on the antenna side, as well as the center conductor of the connector. I've also tested the threads of the NMO connector, vehicle ground, and collar of the PL259. I do not have any conductivity between the antenna lead and ground at any point. I have purchased the new Larsen NMO mounts and will report back when I get them installed.

My old NMO lip mounts were from Pro-AM, and it wasn't until I went to the local radio shop that I was informed that Pro-AM is probably the worst brand of equipment I could have possibly bought. I realize that now looking at the NMO connectors on the trunk lip mount: they paint the threaded part black. That certainly can't help with SWR.

[btrains]

Update:

Currently I have both antennas mounted and I tested each individually with an SWR meter. Right now, both antennas are at 2:1 average SWR. I say average because as soon as I key the mic, each antenna starts at about 2.5:1 and eventually drops to about 1.8:1. Granted these tests were with the vehicle not running, so there may be an issue with low voltage until the capacitors in the radio are charged.

As for the antennas themselves, right now I've had to remove all springs from the antennas, even though I cut them to frequency with the spring length added. As I removed the springs, I noticed the SWR improve. I have a backup whip for 10 meters, so I may as well just start cutting about 1/4" at a time off of my already cut whip and see what happens. At this point, if I can find a match of 1.5 or so, I'll be happy. Then I will have to try the 6 meter whip and cut it down 1/4" at a time.

I should have prefaced this: there are other antennas on the trunk, so it is possible I am getting interference. I have a 1/4 wave VHF and a 3 dB UHF whip for transmit, and a 1/4 wave VHF air band whip for receive only. The VHF TX whip is in the center of the trunk, and I get about 1.5:1 at the band edges, and around 1.2:1 in the center. I am swapping UHF radios at the moment, so I cannot test UHF right now. The air band whip doesn't interfere (at least in the opinion of the SWR meter) with the VHF whip, which is good, considering their close proximity.

[Wowbagger]

VSWR changing as you key would tend to suggest heating within the antenna coils, causing them to drift. Is there a way you can test at lower power, and see if the drift happens more slowly?

[Jim202]

VSWR changing as you key would tend to suggest heating within the antenna coils, causing them to drift. Is there a way you can test at lower power, and see if the drift happens more slowly?

I would have to lean on the battery voltage dropping down in TX due to the engine not running as stated above.

Jim

[wx4cbh]

Astro Spectra asked if you were doing the swr checks outside, and though I could be missing it, I didn't see if you replied. Low band really hates inside locations due to the longer wavelengths making it nearly impossible to get far enough away from proximal objects, and if you're doing the checks inside, expect to see nothing accurate on the meter. Your calculated lengths with the springs may be perfectly good and the real problem is the proximity and reflectivity characteristics of nearby objects and structures. For what it's worth, a 5/8 wave VHF high band antenna can also be affected by proximal objects, whereas a 1/4 wave antenna screwed onto the same mount may show little or no effects due to the greater distance of near objects from the radiating element. RF, smoke and mirrors, snake oil.....same rules apply sometimes.

[btrains]

Yes, all tests are done outside. I do not have a garage to work in. Also, the Syntor X9000 has one power level: 110 watts. It automatically lowers based on SWR, but the radio cannot be set for much lower than I believe 75 watts. I also have another update to this nightmare:

This entire time, I have been doing the SWR checks with the trunk slightly ajar. Basically shut except not latched, so I can run the coax out of the vehicle to a location where I can view my SWR meter. This was giving me the SWR values of about 2:1 with drifting down to 1.5:1. So today I rerouted my coax for testing so I can fully shut the trunk. Now, both whips are back to non-tunable. The 6 meter whip has an SWR of 10:1 or greater, but the radio will transmit at about 45 watts. I tried adding one, and then two, lengthening springs, but they did not change the SWR.

The 10 meter whip is so out of tune that my radio instantly resets to the SELF CHECK display and returns to the last channel I was on. I can't even get an SWR reading it is that bad. I then took my uncut 10 meter whip and placed it on the 10 meter coil, and got about 10:1. I also tested with one, and then two, lengthening springs, and the SWR did not improve from 10:1.

At this point, I have no idea what else to do. My tools are limited to a digital multimeter and a 1.6-60 MHz SWR meter. I feel I have only two options: either throw the X9000 out, which I don't want to do because I've dumped a good amount of time and money into it, or find a mount on the car where I can do 6 meters with good SWR, and check the 10 meter SWR at this location. If it doesn't work for 10 meters, I'm going to program those frequencies out and never use 10 meters FM.

[VE3HKB]

There's something about this that isn't adding up. SWR usually doesn't change during transmit unless there's water in the cable, or the mount is badly corroded. Pushing 110W into a badly tuned antenna can do all sorts of weird things to coils and cables from heating and/or arcing. I think it may be time to step back and start over.
Firstly, get a dummy load that can handle 150W continuous. Make sure your radio's output is stable in both bands while transmitting into the load. This will give you a idea of what power levels you can expect when tuning the antennas, and will also indicate if you have DC supply issues (100W radios draw a lot of current, and if you can't keep the necessary voltage to the radio your power will vary as will your readings.)
The diplexer instructions assume that each antenna is tuned for 1.5:1 (max) so don't introduce it into the system until you have two properly functioning antennas. Every low band antenna I've seen requires lots of ground plane. The centre of the roof is usually the best location, with the centre of the trunk a compromise due to smaller area, questionable ground, and obstructions. If you have to position every thing on the trunk the 10m should be on the centre NMO mount.
The NMO27 is correct for the 10m band, but I missed what you are using for 6m. If it is also an NMO mount, you should be able to use the centre mount for tuning both whips individually. When tuned, the mounting location will alter the SWR a bit, but not to the extent you've experienced (10:1). If the whip (& coil) are not resonant, everything will have an effect.
Also, the more an antenna is shortened from 1/4 wave, the harder it is to tune, with adjustments of no more than 1/8" at a time. Adding 3" springs would likely not make much difference if the antenna is out of tune. Moving from a magnet mount to an NMO mount shouldn't make a difference, but it does. Mag mounts rely on the proximity of the base to the surface to act as a capacitor. This is really only effective for UHF and higher frequencies, so don't assume that the tuning won't be affected. Pick a spot, mount, then tune.
Howard

[btrains]

There's something about this that isn't adding up. SWR usually doesn't change during transmit unless there's water in the cable, or the mount is badly corroded. Pushing 110W into a badly tuned antenna can do all sorts of weird things to coils and cables from heating and/or arcing. I think it may be time to step back and start over.
Firstly, get a dummy load that can handle 150W continuous. Make sure your radio's output is stable in both bands while transmitting into the load. This will give you a idea of what power levels you can expect when tuning the antennas, and will also indicate if you have DC supply issues (100W radios draw a lot of current, and if you can't keep the necessary voltage to the radio your power will vary as will your readings.)

Done. The radio transmits around 75 watts on 6 meters and around 100 watts on 10 meters. The previous owner dialed back the power output to save the PA deck. Power control is done via a pot on the drawer unit.

The diplexer instructions assume that each antenna is tuned for 1.5:1 (max) so don't introduce it into the system until you have two properly functioning antennas. Every low band antenna I've seen requires lots of ground plane. The centre of the roof is usually the best location, with the centre of the trunk a compromise due to smaller area, questionable ground, and obstructions. If you have to position every thing on the trunk the 10m should be on the centre NMO mount.
The NMO27 is correct for the 10m band, but I missed what you are using for 6m. If it is also an NMO mount, you should be able to use the centre mount for tuning both whips individually. When tuned, the mounting location will alter the SWR a bit, but not to the extent you've experienced (10:1). If the whip (& coil) are not resonant, everything will have an effect.

I am using a Larsen NMOQ whip for 6 meters. It is just a standard NMO base with threads to add any quarter wave (or realistically any whip) to it. The whip I have is a quarter wave whip on 6 meters.

I moved the 6 meter whip to the mount in the center of my trunk, and found my SWR to be 2:1 with no spring, 1.5:1 with one 3" spring, and 1.2:1 with two 3" springs. I placed the 10 meter whip in the same mounting location. The radio continued to reset itself due to SWR. I added one, and then two 3" springs, only to continue to get 10:1 or worse matches. I have also tried using my other NMO27 loaded base, and that one also gives the same results. But if I place this tuned and cut NMO27 antenna on my other vehicle that has a Radio Shack 10 meter mobile radio, I get 1.2-1.5:1 on 10 meters using a magnet mount. I can also get about 1.5-2.0:1 on a magnet mount on the trunk of the Crown Victoria. I have an NMO mount on the roof of the Crown Vic as well. I have tried using this one to test the 10 meter whip. I still do not get a usable match.

Pick a spot, mount, then tune.
Howard

If only it were that simple!

[Jim202]

Are you sure that the set screw has cut the paint and is getting a good ground at the mounting point?

Pull the coax off the radio and check the ground on the coax to the new ground straps you put on the trunk lid. You should see zero ohms or close to it.

Did you cut the length of the coax cable between the trunk lip mount and the radio, or did you leave it at the full 17 foot length? Don't remember now that this thread has been going on for so long. You just might be having some reaction with the length of coax cable.

Again I can't remember if this was asked before or not. Did you solder the shield of the coax to the PL-259 reducer and then solder that to the main body of the PL-259 connector?

Use as short of coax cable as you can on the watt meter jumper to the radio. I would try adding short sections of coax cable between the watt meter and the antenna to see if it makes any difference in the SWR. You might have to try several different lengths to get a good feel if it makes a difference or not.

Jim

[btrains]

My sections of coax are cut according to the Motorola chart for diplex operation. My drilled NMO mount is still standard 17'.

I did not solder the shield to the reducer. I only soldered the shield onto the reducer after attaching the main body (so through the four solder holes).

I have checked the ground between the straps and the PL259s. With my multimeter set to the lowest setting (200), I am getting readings of 0.5 Ohms. This is true across any part of my trunk area and any other grounding location, even for other radios/equipment that is grounded. So, I don't have any sort of strange grounding anomaly compared to other locations on the body of the car. I am using the shortest section of coax I own, that allows me to set the SWR meter outside of the closed trunk. That coax run is around 3 feet or so.