bad swr reading on rfmax cable is this common with different cables need help please I'm confused.

[aapaws]

     I just finished loading the GMRS channels into the radio and decided to do a bench test for swr.  The cable that I used for the bench test was a Larsen NMOKHFCXMPL  with a Laird trab4503 antenna.  That's the pic with the 1.91 swr reading bench test inside.  Go to the jeep and hook up the radio attached to a RFMAX, RNMOV-195-SUM-C-17I cable and used the pctel muf4505ngp antenna check the readings and get 6.86.  Switch to a trab4500n antenna no ground plane needed and get 4.71.  Take the radio out go back to the bench and repeat with original  Larsen cable and 4503 that needs a ground plane again and get the same 1.91 reading. 

     Remove the rfmax cable from the jeep and replace with a Larsen cable same as the bench test above and repeat the process this time the swr with the 4505ngp is 1.01 and with the trab4500n different antenna from bench test I get 2.95.  If I switch the trab4500n no ground plane for the trab4503 I get 1.45.  The mount used is on the passenger side of the jeep 2nd bolt Topsy Jk mount.

I am confused with this so the question is how does a non ground plane antenna work worse and the ground plane antenna work the best? I was under the impression that the fender mounts did not have enough for a ground plane.  Also the cable being that far off with swr I'm glade I did not try to cut the antenna.  Has anyone else had this happen to them?

Thanks

 

 

 

 

 

[Sshannon]

You're running in circles.  Diagnose one problem at a time. Analyze the RFMax cable without the antenna to see if you have a cable problem.  You'll need a 50 ohm dummy load to do that. If you find out the cable is crap, get rid of it.  Once you have a cable that gives you a nice low SWR going into a dummy load, then try different antennas.

It really doesn't take much ground plane for GMRS frequencies.  The ground plane provides balance to the radiating element.

 

[Lscott]

You can save yourself some trouble by testing indoors if you have a magnet mount. Stick it on a good ground plane away from things by several feet. I keep a sheet of duct work sheet metal in the basement for testing small VHF and UHF antennas.
 

[aapaws]

Just got home and rechecked like suggested and the cable is bad.  The rfmax cable gives the high swr but the larsen gives the best signal. Also thought is was funny that the ghost antenna is giving me a better swr over the almost 31" antenna.  larsen and laird trab4503 for the win.

thank you for the help.

 

[aapaws]

forgot to attach to picture

[KAF6045]

39 minutes ago, aapaws said:

Just got home and rechecked like suggested and the cable is bad.  The rfmax cable gives the high swr but the larsen gives the best signal. Also thought is was funny that the ghost antenna is giving me a better swr over the almost 31" antenna.  larsen and laird trab4503 for the win.

Which may just mean that the "long" antenna is not yet tuned for the range you are testing. You really need to sweep the frequency to find out where the best SWR is located (if below 462Mhz, antenna is too long; above 467MHz it is too short -- 465MHz is in the middle of the Simplex/Repeater Output and Repeater Input groups).

Or it is coupling to something nearby (metal siding on a house -- don't try to tune it inside a garage).

[aapaws]

Sorry for getting back so late I was on a small road trip.  I used the ghost antenna with a 1.0 swr for most of the way but switched to the 4505ngp antenna the taller one not the ghost antenna which had the original 1.01 swr when I got to the mountains.  That antenna was swinging in the wind a lot for the trip.  When I came home I tested the antennas outside. The ghost antenna still gets a perfect signal and the taller antenna now gets an extremely high swr of 11.46.  I did not even get to use the radio at all I was on a solo business trip and I only picked up a occasional signal.

It was fine before the trip with an 1.01 also. Now it’s extremely high.  I understand that it was moving but all was tight and I did not hit anything with it just removed to switch antennas.  I starting to think maybe my gauge is bad but the ghost antennas have never changed in the swr range.  The 4503 was always 1.01 to 1.03 every time but does jump to 2.05 for the repeater stations and the 4500n ghost antenna was always 2.95 to 3.45.  The only antenna that seems to have changed is the one that can be adjusted.  

I will try again tomorrow to see if the connections are loose on the Allen heads if not I am hesitant with cutting it because of the original good swr reading.  I don’s understand how it could have that big of a swing unless the antenna moved or went bad somehow or the surecom is bad?  I never ever got a reading that high on any of my original test.  The radio does work great with the smaller 4503 antenna tried out at home with some friends but I figured I would use the larger one for more range and switched when I hit the first rest area gas station.  Glad I did not use it if the swr is true.

[aapaws]

I just noticed in the pic that its not giving me the frequency is this common on this gauge?

 

 

[aapaws]

Forget about the last post on not giving me the frequency I was not holding the button long enough to get it to input.   The numbers still stand on the swr with what I posted above.

[KAF6045]

17 hours ago, aapaws said:

I will try again tomorrow to see if the connections are loose on the Allen heads if not I am hesitant with cutting it because of the original good swr reading.  I don’s understand how it could have that big of a swing unless the antenna moved or went bad somehow or the surecom is bad?  I never ever got a reading that high on any of my original test.  The radio does work great with the smaller 4503 antenna tried out at home with some friends but I figured I would use the larger one for more range and switched when I hit the first rest area gas station.  Glad I did not use it if the swr is true.

A comment: don't test SWR at full power unless you already know you are in a good (<3.0:1) range.

Note your bottom line: 35W going out and 25W coming back in... That's putting 60W on the transmitter final/power transistors (unless that is a 50W rig and automatically rolled back the output power to compensate -- but that is still a rather high loading: 60W on 50W finals?)

You'd be better off with an antenna analyzer or VNA that takes the transmitter out of the system and sends signals in the mW range (for one thing, you won't be annoying anyone listening on the frequency you are testing, and both make sweeping the frequencies easier).

 

FYI: the Laird 4505 variant has a datasheet that shows the BEST SWR at 1.6:1, and that is just under the GMRS simplex frequencies; the antenna should have had enough "give" to be tuned without cutting the whip(s).

 

[aapaws]

Sorry Could not test yesterday it rained all day looks like I have water front property now.  I had retested this morning and still got the high swr.  I cut and retested best I could get was 2.45.  The only equipment I have for this is the one swr meter.  Could you tell me if there is a better one because I don't know if I trust this one?  The radio is a 45 watt radio.

The ghost antenna constantly gets the best results.  Always 1.01 to 1.12 no matter how many times I switched.  Pretty much know I screwed up the other antenna because I cut it to small now its going in the opposite direction up.  Live and learn I'm new to this but the radio works so at least I programmed that right.

Thanks

[Sshannon]

1 hour ago, aapaws said:

The only equipment I have for this is the one swr meter.  Could you tell me if there is a better one because I don't know if I trust this one?  The radio is a 45 watt radio.

As @KAF6045 mentioned, an antenna analyzer is the better tool for what you’re doing, but unless you intend to do this more than once it really doesn’t make much sense to buy one. The most common truly inexpensive type of antenna analyzer is a NanoVNA, but they require a certain amount of fiddling around.  Hobbyists like me enjoy that kind of thing, but if a person just wants a good antenna with a reasonable SWR, I would encourage you to just buy a Midland MXTA26 antenna.  

[aapaws]

Thank you for the quick responses.  I up loaded the pics for the low power as suggested had to program the radio first for low power only had programed for full power.  Attached pics.  The 1.14 swr tied to 4503, 3.82 tied to 4500n, 4.36 tied to 4505ngp.  All test done away from everything.

I also ordered the NanoVNA hopefully be in Wednesday/Thursday next week. 

The 4505 says to cut the length to roughly 11".  At that size it still was over 8 swr as it is now its cut down to 7.25" which is way to small. 

I order a new whip for the 4505 and we will see with the NanoVNA before I start cutting again. 

Also thinking about ordering another gauge this time maybe something better.

 

 

[KAF6045]

1 hour ago, aapaws said:

The 4505 says to cut the length to roughly 11".  At that size it still was over 8 swr as it is now its cut down to 7.25" which is way to small. 

I order a new whip for the 4505 and we will see with the NanoVNA before I start cutting again. 

I haven't seen the manual to comment -- when I looked yesterday, there were something like three or four different companies selling "4505" antennas, and all looked the same. The only one that mentioned "field tuning" also looked like it should have been close enough that just loosening set screws and moving the elements up/down.

1 hour ago, aapaws said:

Also thinking about ordering another gauge this time maybe something better.

Most would refer to that as a meter -- it measures things; in some industries "gauges" only provide go/no-go results (the gauge either fits or doesn't fit the item being checked -- setting spark plug gaps for instance is done with gauges; too large a gap and the gauge for the desired size will be sloppy, too small and gauge won't even go into the gap).

I suspect the next step up, for VHF/UHF (125-525MHz) only, in SWR/Watt-meters might be the MFJ-847. It only displays forward (output) power, reflected power, and resultant SWR. No frequency counter. Just two switches: meter on/off, backlight on/off. Prime reading is forward power, reflected/SWR are smaller characters below that.

SWR meters that cover the UHF range tend to be sort of specialized -- most meters are HF up to maybe VHF (my Diamond SX-200 is 1.8-200MHz, and is not an instant read design; to determine SWR you have to set a switch to "CAL", transmit while rotating a dial on the meter to set the needle to full-scale, then flip the switch to "SWR" to get the ratio).

1 hour ago, aapaws said:

 

 

Have you been trimming from BOTH halves of the unit? That black "torpedo" in the middle is a phasing system; the antenna operates as two phased antennas one above the other, fed from the base. Oh, and the spring unit probably counts as part of the length for the lower section. {Personally, I'd want to get it further away from the hood too -- either raised to the height of the hood top, or out to the side; between the spring and the loading coil I'd be worried about coupling detuning the lower section).

[aapaws]

I'm going to call Pctel on Monday and ask them about the spring and what they think about the issues.  Just seemed funny that the one ghost gets crazy good results 1.1  and the other I would not use over 3+ swr.  I was going to bite the bullet and order the bird 43 seemed like it gets good reviews.  May try the  MFJ-847 first its a lot cheaper. 

I even ran a separate ground wire to the mount just to see if that was some of the problem but no change.

 

I want to say thanks for all the help this is new to me.  I thought the radio programming would be the hardest and its ending up being the antenna.

 

 

[gortex2]

What antenna are you actually using ? Do you have an actual laird PN you can share ? 

[tweiss3]

Are these "no ground plane" antennas, cause based on your photo, you don't have nearly enough ground plane under that antenna as installed.

[Sshannon]

20 hours ago, aapaws said:

I'm going to call Pctel on Monday and ask them about the spring and what they think about the issues.  Just seemed funny that the one ghost gets crazy good results 1.1  and the other I would not use over 3+ swr.  I was going to bite the bullet and order the bird 43 seemed like it gets good reviews.  May try the  MFJ-847 first its a lot cheaper. 

I even ran a separate ground wire to the mount just to see if that was some of the problem but no change.

 

I want to say thanks for all the help this is new to me.  I thought the radio programming would be the hardest and its ending up being the antenna.

 

 

Look, buying a Bird 43 is entirely your choice but it’s really not the easiest tool to use. All it does is tell you how much RF power is passing through a single point in the system. You’ll need the right element and after transmitting in one direction to read the forward power you rotate the element 180° and transmit again to read the reflected power. It’s almost certainly more absolutely accurate than the SW102, but absolute accuracy really isn’t what you need. You’re getting relative readings from your power meter that tell you everything a power meter can tell you. 
An antenna analyzer doesn’t rely on transmitting, in fact you disconnect your transceiver and the analyzer provides all the signals necessary at low power levels to determine the characteristics of your feed line and antenna, separately and together. 
Here’s how I would do it:

1. Remove the antenna and put a dummy load on the antenna end of the coax.  It should show a length of coax that is about right and an impedance of 50 ohms and an SWR of 1:1 or very close.

2. Then reconnect the antenna and sweep it for SWR from about 460 MHz to 470 MHz.  If you use a NanoVNA there are a limited number of data points so I would find the dip and then recalibrate and bracket it. That will tell you where the antenna is closest to resonance.  It will also tell you how low of SWR your installation can achieve.

3. Then try doing one thing at a time to affect the ground plane size to see if it makes a difference. As long as you’re not changing the range of frequencies you’re sweeping you don’t need to recalibrate the NanoVNA.

I can’t emphasize enough that you want to examine one thing at a time until you eliminate everything but those one or two things that are affecting your installation  

 

[aapaws]

Sorry for gettiting back so late.  I just received new antennas cut and tuned for 462 printouts attached.  The 4505ngps has a swr of 2.27 on channel 16 and repeater channel of 2.39.   On the ground plane antenna 4505s its swr 1.74 on channel 16 and on repeater channel 16 its 1.11.    

With the printouts attached would it be worth it to try to trim the antennas anymore.  I am still on the fence if I should try another swr meter because the antennas have been tuned to the frequency as far as I can tell.

 

It’s also funny to me that the Mount I’m using I would have thought the no ground plane antenna would work better.  I wondering if the fenders I’m using is causing a problem they are metal.

thanks 

[aapaws]

Ps I’m still waiting on the NanoVNA the one I order was 3 weeks out.  

[axorlov]

There is a mess with regards to the antenna models, I see three antennas mentioned, one a "ghost" another two whips. The printouts are for 4505S (what is that? 4503S?), another is for 4505NGPS. Hard to make  sense, but lets try.

- The shorter whip appears to be MUF4503S, which is 5/8 antenna;
- The two-element whip appears to be MUF4505NGPS, which is 1/2 over 1/2 antenna? I can't find a good specs for it, but judging on the length of elements it looks like it's 1/2-1/2.

If above is correct, the results for tuned antennas are not surprising.

5/8 antenna will work without ground plane, pattern will be messed up, and gain will be not what it should be when sufficient ground plane is present, but not by much. And, being a single element, it is much easier to tune. That is a virtue of 5/8 antennas: easy to tune for SWR, and they still work under non-ideal conditions.

1/2-1/2 is harder to tune to SWR, due to elements having an effect on each other. Btw, even 1/2 single element is harder to tune than 5/8, it is more sensitive to length. When properly tuned, it should outperform 5/8 with no ground plane, and should have better pattern. It very likely outperforms 5/8 already, with the current SWR 2.3. Do you want to use it as-is or want to tune it more, is between you and your transmitter.

I would go with 5/8, it seems good enough.

 

Edit:

Looking at the printouts, it looks like tiny bit of shortening of the element of 1/2-1/2 will bring SWR down. You can try to do so when NanoVNA comes and you are familiar with it. And do sweeps and tuning in place, on your fender mount.

[aapaws]

I will try shorting it just a little to see what happens maybe a 1/8 inch just to see.

the models are 

https://theantennafarm.com/shop-by-categories/shop-all/mobile-antennas/300-512-mhz-uhf/no-ground-plane-antennas/8346-pctel-maxrad-muf4505ngps-detail

https://theantennafarm.com/shop-by-categories/shop-all/mobile-antennas/300-512-mhz-uhf/high-gain-antennas/8345-pctel-maxrad-muf4505s-detail

https://www.arcantenna.com/products/trab4503-m2m-400-490-mhz-black-low-profile-omni-antenna

https://www.arcantenna.com/products/trab4500n-m2m-400-490-mhz-black-low-profile-omni-antenna

That are the exact antennas.  The trab4500n is total useless and the 4503 is the best for the ghost antennas.

The other whip antennas are the ones above that match the printouts with the tune sheets.  I thought this would be of help with the confusion.  I will tune them again just a little when I get the new meter just to see.  I also ran a separate 10 gauge ground wire just to see if it would help and it did very little.

Thanks for the quick response.

[aapaws]

I started to play around a little with the length.  Got the swr down to 1.35 from 1.74 on reg channel but on repeater channel it went up from 1.11 to 1.49 that was on antenna 4505s whip.   On the 4505ngps I got it down from 2.27 to 1.74 on reg channel and 2.39 to 1.65 on repeater channel.  Don’t think I can tune any better.  

I’m leaving the 4505s whip antenna requires ground plane but gets best signal swr.  

Could it be possible that the metal fenders could be acting as a reflective ground plane even though the mount is 1.5” higher than the fender?

sorry did not take pics of the 4505ngps signal.

thanks 

 

[axorlov]

2 hours ago, aapaws said:

Could it be possible that the metal fenders could be acting as a reflective ground plane even though the mount is 1.5” higher than the fender?

Yes, it can provide reflective plane to some extent. But important to realize that SWR is just a amount of mismatch between antenna and transmitter. In other words, SWR is not a measure of the efficiency of the antenna. Your transmitter will be happy now, but antenna pattern is unknown.