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My SWR's are weird

C

chad68

Member
Dec 20, 2010
13
0
11
I have a Monkey Made MM9 mounted on my bed rail behind my cab on the drivers side. It has a 9" shaft. The coil is about 7" behind the cab. Ideally I should be using a 22 or 27" shaft like the 10K's, which I'm thinking of getting instead of the MM9 I have.

Here's the thing. SWR's are 1.8 and 2.2 when parked outside away from all trees and such. When the truck is parked in my garage the SWR's are 1.2 to about 1.5.

Why the hell would they be lower parked inside a tiny one car garage?

Another thing is with my Wilson mag mount they are 1.1-1.3 outside and then go off the chart in the garage. The mag mount SWR's react the opposite way of the other antenna. What the Wilson does makes sense but the MM9 thing confuses the hell out of me.

I know why the MM9 is high outside, because of where it's mounted with the coil at the wrong height and a crappy ground plane but I can't figure out why they are so much better in my garage.

On a different note, anybody make a 3/8"x24 thread extension shaft for these types of antennas, like say about 12-15" extension?

If I can get the bottom of the coil above the roof line any guesses on how much I might expect to drop the SWR's? I would be happy with 1.5 or less. Even with 2.0'ish SWR's the MM9 gets out and receives fine.

So for now I'm thinking of getting an extension, just buying a long shaft 10K or just go back to a Wilson 1000.

Sorry about all the freakin' questions.

I will try to see if I can figure out how to upload the pic.

http://i648.photobucket.com/albums/uu205/chad68/anten003.jpg
 

The part of the antenna above the coil is the part that is putting out your signal. The coil just lets you use a whip that is less than 102" in length. If you have a whip in the antenna that is too short that is what is causing your weird swr readings.
 
SWR will change with what's around an antenna, inside or outside. Having it go down is a bit different, but still not that uncommon, when inside a building. All I'd make a guess at is that the thing could be tuned better.
The coil not clearing the cab does contribute to part of the problem. Raising it with an extension would help that particular part of it. "Gunny" (CBRT forum) makes those extensions, don't have his site's address, sorry. No idea what the prices are, you'd have to go see. Also have no idea of the quality, I've never had my hands on one. I don't have any reason to think they would be bad though.
Good luck with it.
- 'Doc
 
MrSuburban said:
I am sorry this is a pet peeve of mine ...It is called SWR not SWR's
Click to expand...
SWR's, RMS, ground wave etc are all bad terminology, like Garth once said, it takes the same effort to learn the proper terminology as it does the incorrect terminology ;)
 
359 said:
SWR's, RMS, ground wave etc are all bad terminology, like Garth once said, it takes the same effort to learn the proper terminology as it does the incorrect terminology ;)
Click to expand...

Not really ground wave, and Rms = root mean square are ok

SWR's is just bad grammer LOL ;)
 
MrSuburban said:
Not really ground wave, and Rms = root mean square are ok

SWR's is just bad grammer LOL ;)
Click to expand...
Ground wave is non-existent at 11m, where the term is used the most and there is no meaningful use to express RF as RMS, AVG is what people are referring to, not RMS.

EDIT____
While we're on the subject of pet peeves, AB1 biased transistors are right up there too, lol
 
Last edited:
MrSuburban said:
I am sorry this is a pet peeve of mine ...It is called SWR not SWR's
Click to expand...

I was calling them SWR's because they're different on 1 and 40 LOL. Good point though. On the other hand if they are higher than 1:1 than you would have multiples ('s) LOL.

I know what you mean, I hate it when people talk about "driving" a motorcycle.

edit:

"My SWR readings!"
 
chad68 said:
I have a Monkey Made MM9 mounted on my bed rail behind my cab on the drivers side. It has a 9" shaft. The coil is about 7" behind the cab. Ideally I should be using a 22 or 27" shaft like the 10K's, which I'm thinking of getting instead of the MM9 I have.

Here's the thing. SWR's are 1.8 and 2.2 when parked outside away from all trees and such. When the truck is parked in my garage the SWR's are 1.2 to about 1.5.

Why the hell would they be lower parked inside a tiny one car garage?

Another thing is with my Wilson mag mount they are 1.1-1.3 outside and then go off the chart in the garage. The mag mount SWR's react the opposite way of the other antenna. What the Wilson does makes sense but the MM9 thing confuses the hell out of me.

I know why the MM9 is high outside, because of where it's mounted with the coil at the wrong height and a crappy ground plane but I can't figure out why they are so much better in my garage.

On a different note, anybody make a 3/8"x24 thread extension shaft for these types of antennas, like say about 12-15" extension?

If I can get the bottom of the coil above the roof line any guesses on how much I might expect to drop the SWR's? I would be happy with 1.5 or less. Even with 2.0'ish SWR's the MM9 gets out and receives fine.

So for now I'm thinking of getting an extension, just buying a long shaft 10K or just go back to a Wilson 1000.

Sorry about all the freakin' questions.

I will try to see if I can figure out how to upload the pic.

http://i648.photobucket.com/albums/uu205/chad68/anten003.jpg
Click to expand...
well id get a tram tri mount then mount it on the roof
this will probly get your swr down to 1.5 or less from
your first post ya stated you had 1.8-2.2 so that tells me
ya may need to trim 1/4 inch or so off the bottom of whip
but i wouldnt until ya relocate the antenna.as to why it read
ok in garage ...no idea. but i wouldnt use that reading
 
The best I have been able to get the reading now with the MM9 is 1.6 on 40 and 1.7 on channel 1. That is with it still mounted behind the cab. I think that's about as good as it's gonna get mounted there. Right now I'm using 9 or 12 feet of coax. I picked up some 18 foot stuff, so I will see if that makes any diff, since I'm going to need the longer coax when I get my new radio anyway.

For the hell of it I bought a 4" Wilson silver tip. Wow can barely get the SWR readings below 3. Instructions indicate I need a longer tip. I have an extra whip that will fit but doubt I'm gonna even bother with that antenna. Maybe if I get bored enough I will try a longer tip.

Also bought a 2 foot non adjustable stick just for using as a 99% recieve only antenna. It recieves and gets out at least 5 miles at night (even in my garage). For some reason any antenna I mount behind the cab has lower swr readings than when parked outside in an open field and they all get out about 5 miles parked in my garage. Some wierd vortex, Twilight Zone stuff going on in my garage.

I'm toying with the idea of getting a tram tri mount and getting the roof clear bra'd and trying the MM9 and trying a 102 and see how that goes.

In the end I will probablly end up using a 10K double coil SW with 17" shaft behind the cab, just because it's the most convienent spot, since I have to take a whip off several times a week and will fit inside my cab when not in use.
 
You probably need to pay more attention to your vehicle body as a counterpoise for your antenna. No matter what kind of antenna you try.
Often pickup truck beds are mounted on rubber, and dont have good electrical connection to rest of truck frame for the purpose of radio frequency. It often requires braided straps to improve the situation. Its usually most helpful to have a braided strap directly between the cabin frame and truck bed frame for that type of vehicle. This become more important if you want to run big amplifier.

Should not be concerned with swr in a garage, because there can be lots of metal around.
What matters is the performance in an open area without stray metal around.

I also must wonder if your truck bed is plastic on the outside, and how much metal is really there, because your antenna must be mounted on metal.
 
I ran into the same problem on my dodge dually when I went with the p-10k. I was using a 30" shaft and was way above the roof line with the coil but you have to remember that you dont just radiate from the tip of the antenna or above the coil so you get reflection off the cab of the truck when you are that close. The ideal mount is a puck mount in the roof but if you are like me Im not doing that. I drive through the woods and it just wouldnt work. I moved mine to the right rear corner of the bed and my reflect dropped way down. My swr is right around 1.1 but it does make you somewhat directional..
 

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