In lieu of through hole mobile mounting...

[TheBlaster]

I mirror mount, when I use a whip, through hole is impossible on my vehicle.

Any technical info to suggest that self made ground planes attached to my mirror mount bracket with strong crocodile clips close to feed point will broadly increase antenna efficiency ? (extra counterpoise for it to work off)

Or would putting some 6 x 5 foot metal poles 6 inches apart under the vehicle roughly where the antenna is mounted on the ground reduce ground losses at all ?

Just thinking out of the box for a little extra performance, feel free to shoot me down in flames.

This is possible to test in reality of course but is there any theory that would give prior insight before doing a test with a local at some juncture ? Thanks

I am loosely resting my thought on this page:

http://www.k0bg.com/eff.html

 

[secret squirrel]

What type of antenna and mount are you using? Is there a problem you are trying to fix or just tune everything the best you can do.

 

[TheBlaster]

All working fine, it is an optimization question and relates only to static mobile operation.

Thanks, I am using a 3/8 whip connector/ SO-239 fed mirror mount, stainless steel attached to an aluminium rear reversing mirror arm on a high 2M high vehicle. This mirror arm is conductively metal to metal coupled to the rear door (and I bonded the rear door to the rear side panel) I maximized metal to metal conductivity throughout but of course the ideal is through the roof with a large area of steel (middle of a roof) and I want to try and minimize any losses by creating "add ons" if possible.

I feed it with the shortest amount of Super 8 (mini8) cable I can with a 5 turn choke just before feed point. In total about 2.5 meters of cable for negligible cable losses, I shortened it so there is just enough to get it to my transceivers position.

I am additionally thinking that I may be able to G Clamp an aluminium pole at the feed point (as in... right under the vertical antenna) that may help create some form of extra counterpoise.

I am obtaining a very good SWR 1.2:1 and the antenna/s (centre load and a self made tank whip) seem to work pretty well, but you know how it is, improvements are improvements, and if easily obtained, something I am interested in.

Even leaning 2 x 10 foot poles against the mount is feasible and could act as some kind of additional counterpoise.

I suspect the proof in the pudding will be in its eating, which can be fun, but wonder if anyone has done this stuff before. I have seen mirror mounts with what would appear to be a largely pointless 12 inch ground plane stub (image attached) so if I can build on that with any metal structure under the feedpoint to make it "better" than I would like to.

 

[secret squirrel]

https://www.qsl.net/kk4obi/Center-fed L-dipoles Vertical.html

Check out this link. Look at Vertical L Antenna. By adjusting the angle of the lower leg it affects the radiation pattern and the antenna impedance to maintain low SWR. in theory you may be able to direct radiation forward and keep matching impedance. Hope this offers some help. There are a lot more knowledgeable gentleman on this forum than me on these matters.

 

[TheBlaster]

Thanks, I had suspicions some degree of directionality and impedance change may result from "add ons". The antenna will be somewhat direction as it is already mounted
at one end of the vehicle instead of centrally mounted. So it would be uncertain as to how it may affect the pattern.

In fact this can be potentially used to advantage to a small degree, sling shot-ing the energy (and RX) a little more in one direction than another.

I would have to consider any signal report changes may relate to changes directionality
as much as globally improved field strengths.

In short I gather from the link I supplied that more ground losses = less low angle radiation. I want to think about this and experiment but the complex interactions are clearly impossible to understand without technical measurement equipment.

 

[Handy Andy]

It's the crocodile Clips" - did you mean Battery Cable type of clamp or something more like a push nut, C-Clip type of install? Like a Pinching of two plates.

The "pinch points" would not be the best at being RF conductive - may be more of a problem than what you have now when it comes to noise.

Saw the reference to the "downward" tuning stub...although "Cute" only provides a matching solution to a problem you still will have.

Remember that RF uses the "skin effect" so it tends to use surface finish metal more than the body - but due to the nature of ground loops, current and noise and the eddies that form from their distance and the proximity of long runs. Want to advise you that due to the nature of RF wanting to use such skin - you may be better off simply developing a function of tubing and reinforcement- to make an antenna "array" mount - you gain surface area for the counterpoise you're looking for.

Seen many trucks and vehicles use Satellite receiver mounts ADDED onto the Mirror brackets to enlarge the mounting surface. There's side benefits - it's adding torque and tensile strength as well as provide a better counterpoise for RF using both the pillar and mirror bracket for the door.

 

[TheBlaster]

These are croc clips, I see your point about noise and the pinch points, even light wind might make these scratch around on the surface of the mirror mount.

 

[midnight special]

maybe this is what you could use,,,, https://mfjenterprises.com/products/mfj-347

 

[TheBlaster]

Yes that is what I am using now, I am considering adding to its bulk to create a greater counterpoise that the vehicle body can give now. (given it is supposedly not the optimal way to mount compared with through hole in middle of roof - which is impossible)

 

[M0GVZ]

If it's purely for static mobile just get four lengths of wire, approx 9ft long (reduce by 5% if using insulated wire) and four long stakes. Hammer the stakes into the ground leaving three feet or so sticking out, bring the wires off the mounting bracket in a X pattern attaching them to the top of the stakes. Doesn't matter if one or more is laying across the body of the vehicle. Hey presto, one elevated radial system that'll work pretty well. You'll know if it's working well by the fact the SWR should go down on the lower channels and be lower than that of the upper channels because as you improve the RF ground the resonant frequency of your antenna drops so you need a shorter one for a given frequency.

 

[Slowmover]

These are croc clips, I see your point about noise and the pinch points, even light wind might make these scratch around on the surface of the mirror mount.

I must’ve graduated high school in the 1970s. Had a different name, then.
.

 

[TheBlaster]

If it's purely for static mobile just get four lengths of wire, approx 9ft long (reduce by 5% if using insulated wire) and four long stakes. Hammer the stakes into the ground leaving three feet or so sticking out, bring the wires off the mounting bracket in a X pattern attaching them to the top of the stakes. Doesn't matter if one or more is laying across the body of the vehicle. Hey presto, one elevated radial system that'll work pretty well. You'll know if it's working well by the fact the SWR should go down on the lower channels and be lower than that of the upper channels because as you improve the RF ground the resonant frequency of your antenna drops so you need a shorter one for a given frequency.

That seems like it would work, less the hammering them into the ground, static mobile often means you are on tarmac and less so a field. However in my mind there is a balance between the convenience of a whip mounted on a vehicle with any "add ons" and going the whole hog and sticking one of my 1/2 wave's up.

I would use a base station antenna for uncompromised performance but if it is a less comfortable or more awkward QTH location I like the ability to drive off and be unattached to anything if need be.

I will definitely consider this, I initially discounted long radials but 3 x 102 inch radials spread could be the perfect compromise in some situations like some kind of hybrid vehicle GPA (Ground plane Antenna, especially if using a tank whip)

Good replies all, thanks..

 

[TheBlaster]

I must’ve graduated high school in the 1970s. Had a different name, then.
.

Might be just the U.K. nomenclature.

 

[Slowmover]

Might be just the U.K. nomenclature.

There, a reptile. Here, an insect.

Roach clip: archaic slang for this device used to hold “the roach”; the tiny butt end of a marijuana cig.

A 1970s artifact.



.

 

[Slowmover]

How did the tests go?