Antenna placement question?

[WSEZ903]

I have a Subaru Forester Sport that I have a Tram 5.5" mag mount with a Browning UHF gain antenna that I have cut to 467 MHz.  I have purchased direct mount to the roof but I want to drill once and be done.  Question is when I place the mag mount in the middle in front of the shark fin by a few inches I get an SWR of 1.7 of higher.  If I move it in between the shark fin and the side rails on passenger side it drops to 1.5 +/-.  If I move it to the same spot on divers side I get about 1.3 +/-.  The back of the vehicle does have a fiberglass/plastic cowling for rear window and more towards the front I have the "Moon Roof" as they call it.  I do have a roof rack that I put on once in a while and with it on or off I did not notice any gain or loss in SWR when testing with it on the sides.  The roof rack rail in attached picture in the back I have moved forward and all the way back and it did not really affect the reading.  I.e. 1.52 vs 1.56.

Any thoughts as to why it is lower on the drivers side vs center?  Attached is a screen shot of my roof.  Side note the passenger side black rectangle that looks like it is on roof rack it the thumb screw for 360 camera mount.

Edited November 22, 2024 by WSEZ903
Mis spelled word.

[WRYZ926]

Double check to see what the SWR is currently on 467.550 and 467.725 before you make any adjustments. It's always easier to make the antenna shorter verses trying to lengthen it after cutting.

[WSEZ903]

2.10 on 550 and 2.20 on 725

 

i put the midland mxta26 on and it is at 1.10 (550) and 1.7-1.9 (725) Ironically it was a lot higher with mag mount so I went with the Browning BR-450 instead as I had installed them in the past on vehicles and no issues.
 

I have it (browning ) cut to 470, now thinking I don’t know why and it might be a tad too short.   I will see if I can find where I can but a new bottom rod or just order a new antenna and deal with the loss.  I have the midland in there for now. Midland is ok, but browning seems to have a better signal to me. 

[WSEZ903]

OK  so I had added a reply twice since my last but it did not post for what ever reason.  

I actually cut the antenna to 470 for what ever reason.  I honestly do not know what I was thinking.  So I ordered a new one and cut it to the 465 are.  Did a test and SWR was 1.80-85 area.  Took about 3 mil off and now 2.2.  I guess i need it  longer or I am not measuring the correct spot when cutting?  I also have the midland gain antenna that I get a bit of a better reading on but it does not pick up as well.  So, I took the original Browning BR-450 antenna and put it back on for the time being as it is below 2.0. 

Thanks for all the help in this. It is really appreciated.

[SteveShannon]

7 hours ago, WSEZ903 said:

OK  so I had added a reply twice since my last but it did not post for what ever reason.  

I actually cut the antenna to 470 for what ever reason.  I honestly do not know what I was thinking.  So I ordered a new one and cut it to the 465 are.  Did a test and SWR was 1.80-85 area.  Took about 3 mil off and now 2.2.  I guess i need it  longer or I am not measuring the correct spot when cutting?  I also have the midland gain antenna that I get a bit of a better reading on but it does not pick up as well.  So, I took the original Browning BR-450 antenna and put it back on for the time being as it is below 2.0. 

Thanks for all the help in this. It is really appreciated.

Is the Browning a higher Q antenna?   How wide is the dip? You’ve been aiming at 465.xxx MHz. How is it at 467.xxx MHz?  Do you have someone you could borrow an antenna analyzer from?  A cheap NanoVNA will sweep the SWR so you can see what the response is across a range of frequencies. It could save you the expense of going through antennas. 
Is it just a piece of stainless steel whip you need to replace the one you trimmed? Sometimes auto parts stores have replacement whips.

[WSEZ903]

I will ask around.  It is the browning BR-450 https://a.co/d/0DDe9XK. Amazon link. 
 

this is with the original one I had purchased that I put back on. 462 is fine. 467 is a bit higher.pictures attached. 
 

I will check an auto parts store for other whips. Home Depot was going to be my guess.   My goal is to get the 467 side to 1.25 or better.  Just figured it would help prolong the life of the radio. 

[LeoG]

I know this is more about placing an antenna on a vehicle and having directional qualities because of where you place it but I have a weird dilemma with a base antenna

I've had the same antenna on my small repeater at my shop and it has given me mediocre results ever since I put it up there.  After we had some wind my cheap mount folded and the antenna leaned.  I straightened it up and reinforced it best I could and life went on.

Then another agressive wind came around for a solid week and the mount failed again.  The antenna was at about a 15º lean and the repeater was contacting my house very well.  Thought it was odd.  So after the winds died down after a week I got a much sturdier replacement for my mount and got the antenna up vertical again.  It's about 2' lower because I separated the mounting brackets more to take the leverage the wind produces on the mast.

I could get to my house base station, the wife said I was coming in great.  She on the other hand was barely making the repeater.  And when she was it was horrible.  So last night I started testing with a voice activated recorder.  Driving away from the repeater toward the house calling out at different streets til I reached my driveway, tested there with an HT and then in the house testing the base station. 

I did this 4 times with not great results.  Found that the HT I use normally in the shop wasn't doing a great job and swapped it out.  Tested in the shop and then in the office.  I went up on my ladder and loosened up the mount and turned the antenna about 10º and now it started to come in better.  I still don't know as of yet if it'll work as good as the test I did last night.  But that test was very good.  It always comes in better later at night than in the normal work hour time.

So I'm just wondering why my omnidirectional antenna seems to be far from omnidirectional.  Seems like there is a distinct lobe that has a 20dB or more lack of power.  The repeater is about 42 watts and the house base is 25 watts, both measured out the backside of the radio.  House is 84' LMR400 and the shop is 50' LMR400.  It's line of sight but heavily treed.

More testing will be done today, this time not all by myself.

[WRYZ926]

Here is a video where a guy played with the antenna height on his dual band antenna to find out what worked best for his location. He was in a bit of a hole with lots of trees around. He found that having the antenna up as high as he could get was not the best solution.

Nitpicking the Height of My 2m/70cm Base Station Antenna

[LeoG]

Yup.  multipath reflections can really affect reception/transmission if you get your antenna in just the wrong position.  In the house receiving a weak station moving the HT just a few inches can make or break the reception.  Same exact thing for an outdoor antenna I would assume.

All summer long I was receiving a repeater and the signal was great.  I figured as winter approached and the leaves fell off it would only get better.  Was really wrong about that.  The signal degraded by a huge factor to the point where sometimes it was getting under the squelch and I had to lower it.  Now that we are in full winter, all leaves that are going to fall have.  The signal is better but nothing like it is in the summer.  I assume it's just multipath interference and antenna position.

[WRYZ926]

Propagation can definitely change between the different seasons. Location and local terrain factors in too. Basically the shorter the wave length is the more vegetation will affect signal propagation. Analog TV stations are another examples. the VHF channels will not be affected as much by foliage compared to the UHF channels. Same goes for two way radios. 

I have learned to despise cedar and pine trees. They definitely mess with UHF frequencies.

I travel down two paved county roads to get to the closest VA hospital. There are plenty of valleys and forested areas. And is some places there are a lot of red cedar trees growing close to the road. I have quite a few spots where I have a hard time getting into the 70cm and GMRS repeaters while I have no problems getting into the 2m repeater.