Antenna Question?

[dnguillory]

So I have my nmo through roof mount at back center of roof on my dodge megacab. Sunroof so SWR is better near the back. I can use my tram 1140, browning BR140, Larsen nmo27, or laird C-27 (I'm obsessive). It works well and get good receive and decent output range. I also have a predator 10k on a flat bracket in center of top of headache rack. 1.1:1 SWR on all 40. It is wider bandwidth and I'm convinced that TX range is better. For some reason it seems my receive is not as good as the through roof. Again, I'm obsessive so keep that in mind, but could the nmo do better overall because of ground plane than my 10k? The 10k is on a 9" shaft and it is total about 63". The nmo antennas are only about 52-53" total with base. Im told I should be using a 17" shaft so coil is higher but the whole antenna is completely above roof and not obstructed.

Does the 10k have better transmit range on both tx/rx or does the through roof have an overall better chance? I switch between my galaxy dx-48T, cobra 29lx with x-force x-80, my hr2510 with palomar 250, and my magnum 257hp.
I want to use a 4pill amp with my 29lx (better sounding tx and very better receive than the Galaxy). Don't know how, but the receive on the 29lx and HR2510 is much better than the Galaxy. The receive on the magnum is noisy but the tx/rx audio is unmatched.
My nmo antenna handle my amps now, but a 4pill will explode off the roof.
Am I nuts and can anyone weigh in? Thanks in advance.

[The DB]

The first thing about antenna performance is the higher the antenna is mounted the better it will perform.

The second thing about antenna performance is the longer antennas outperform shorter antennas.

The third thing about antenna performance is if you have a shortened antenna, including every mobile antenna shorter than a 102 inch whip, the higher the loading coil the more efficient the antenna will be, and thus the better the antenna will perform. Although this one has a caveat, to make any real difference you would actually notice you need the coil to be at least half way up the antenna, which will never happen with the Predator antenna design for several reasons, mostly mechanical in nature. That being said, that doesn't mean that there aren't other non-performance benefits for moving the load up the antenna some as well. For example, if you are having trouble tuning the antenna it has been reported that tuning a Predator antenna can be made easier if you have a longer shaft. As yours seems to be tuned fine I wouldn't worry about it.

Also a note, the same aspects that makes an antenna transmit well also make the antenna receive well. These two aspects are directly related to each other, it is called reciprocacy and has been demonstrated to be true when applied to actual antennas and accurate measuring equipment in the strange and wonderful place called "the real world"...


The DB

[MDYoungblood]

The reason the roof mounts work better than the rack mount is a capacitance problem, the front half (I am talking counter poise) is fine but the back half has to drop to the bed level. You are seeing a good SWR because of the front half. Here is a quick trick to figure out what I'm talking about, take 2 wires from the mount's ground naturally and run them to the back of the bed, one on each side of the tailgate, you will see an improvement inbothTX and RX. They can be sloped to the back but have to start at the mount, length doesn't matter.

3's

Greg

[dnguillory]

Thank you both (db and Greg). I will try that. Yeah, the bed is a CM flatbed in which the headache rack is welded to bed all together. For those reading, in my humble opinion, I like the nmo base loaded antennas for pickups. You can barely see them aesthetically, the perform damn good for a barefoot radio, if the only option is a magnet Wilson 5000 or 1000, or even through roof, I would opt for one of them first. If you don't need to run more than a 40-50w dead key.

Greg,
What kind of wire should I use for the down-riggers you suggested?

[MDYoungblood]

Anything will work, 14 gauge is an all around wire, like everything else bigger is better but not just to try. I've had a couple of rollbacks installs and I used an aluminum pizza pan as a counterpoise (takeoff point for the signal), looked funny but worked great.

3's

Greg

[dnguillory]

Ok. Sounds good.

-- Sunday, 26 April 2015, 19:25 PM --

What about RG6 coax? I have loads of it. Can I strip and put ring tips on the shielding on both ends and leave the coax whole? Thanks again.

(edited by MDY, please remember this is a family forum)

[MDYoungblood]

RG6 is 75ohm, it's for TV, Cable, Satellite and stuff. It can be made to work but it wouldn't be efficient. Good quality coax and antenna will make it a one time install.

3's

Greg

[dnguillory]

Greg,
I have rg8 run for antenna but was wondering if rg6 would work for the two counterpoise wires you spoke of.

[MDYoungblood]

Okay, boy I need to start back reading. Yes it will be fine, hook the center and shield together to make one wire out of it. After you try that and it works, (yes it will work), you could add more, one to the center and two more to the sides. If they would make a metal spider web bed net, it would be great.
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3's

Greg

[dnguillory]

awesome. thanks

[MDYoungblood]

Did it work?

3's

Greg

[dnguillory]

Greg,
before I tried it, I put my W1000 through roof and am using it for now so I could put that one on another vehicle. I will definitely try it on that vehicle because im sure I will need to. this weekend more than likely. thank you for the follow-up.