steel mesh for mobile 2/70 antenna?

[mjac]

Ok, good info I am sure. But ya'll have officially reached over my head levels. I'll return to lurk mode now, carry on.

Bill, Ih8mud is a bit dated and LC focused but I did see one or two earlier Gen T4R antenna mount examples. Several lip on hatch arrangements.

Looking forward CFW and what options it may present.

 

[Tennmogger]

It's probably best to use an antenna analyzer and a reflected power meter.

There is no conceivable way that anyone on the internet can remotely evaluate your antenna!

You could spend all the money in the world on random antenna bits because the internet told you to, but with an antenna analyzer, you could build a two meter antenna out of rusty fence wire. buy one!!

That said, the reason why you haven't seen much about ground plane requirements for any antenna is because there isn't one. There's no universal equation. If you're mounting a vertical antenna on a vehicle, you may not be far enough from the ground to experience strong issues in impedance or reflectance due a lack of a ground plane. (proper or not.)

But in the end, you can't tell evaluate the difference between a pie tin, a wire mesh, or radial counterpoise - or whether or not you even "need" a ground plane without the proper equipment.

Hi Sonoronos, I hope I have simply misunderstood some of your comments. First, an antenna fits somewhere between a device that radiates radio energy perfectly, and one that radiates nothing (like a dummy load). Both those extremes, and all in between, can have 50 Ohm resistive response and look great on an antenna analyzer or SWR meter. So, an antenna analyzer might be the worst device to evaluate how well an antenna radiates.

As for finding out what works from questioning actual users on the internet, I would choose that first, rather than relying only on an antenna analyzer, for the above reason. That said, I also use an antenna analyzer, or an SWR meter, or a forward/reverse power meter to verify 50 Ohm resistive (or deviation from it) After the antenna has been designed from experience and experimentation, the type info commonly found on the internet. Then evaluate the antenna's real performance with a field strength meter, or talking to your buddy, LOL.

A ground plane is absolutely defined as part of an antenna system for most common vehicular antennas. The exception might be the half-wave mobile antennas sold as "no ground plane required", but, even those have been optimized to work when a vehicle IS under the antenna.

Bob

 

[nemoaz]

Conceptually, fender mounts are bad, duckies are bad, glass mounts are bad, magnet mounts are bad, and lack of ground plane is bad, yet many people get by with one or several of the above.

 

[Hilldweller]

.... Then evaluate the antenna's real performance with a field strength meter,...
Bob

The FieldFox works great as a field strength meter.

I ran up 515 yesterday to try and ping that repeater in Cleveland that you like. I got it the other day near my house when 2M was propagating like crazy. But yesterday it was just lousy.

I was playing with other repeaters in the area: 145.3700 (-) PL 103.5 is a good one for CFW. 146.805 (+) PL 100 is still the best around but has too much traffic for us to use for an event.
I spoke with one of the clubbers that maintains 145.37 and he said it's fine for us to use it for CFW.

 

[taliv]

hey Bill, are you bringing the drool-worthy keysight stuff to CFW?
I will be lucky to get my 2m/70cm antenna installed by then. tarheel stubby will probably still be sitting in garage. trying to figure out where to put it on the new rig. thinking about putting my j-pole and long wire tuner on the trailer when it gets in end of january.

 

[Hilldweller]

hey Bill, are you bringing the drool-worthy keysight stuff to CFW?....

I have a standing invitation to borrow the FieldFox ----- but the dang thing costs over $18k and it makes my stomach flip thinking of bringing it camping... Too much going on.
I've invited people to come by the lab and chat with the RF engineers for years and only a few have come. ....and now they're moving downtown.
I'm sure I'll keep in touch with a few of them but I won't have access to the meters anymore in a month.

One of the guys goes to HAM meetings every now and then. If we can get a guaranteed group I'll try to arrange a field day with him and a good meter.

 

[taliv]

totally understand

 

[jonny123]

It's probably best to use an antenna analyzer and a reflected power meter.

There is no conceivable way that anyone on the internet can remotely evaluate your antenna!

You could spend all the money in the world on random antenna bits because the internet told you to, but with an antenna analyzer, you could build a two meter antenna out of rusty fence wire. buy one!!

That said, the reason why you haven't seen much about ground plane requirements for any antenna is because there isn't one. There's no universal equation. If you're mounting a vertical antenna on a vehicle, you may not be far enough from the ground to experience strong issues in impedance or reflectance due a lack of a ground plane. (proper or not.)

But in the end, you can't tell evaluate the difference between a pie tin, a wire mesh, or radial counterpoise - or whether or not you even "need" a ground plane without the proper equipment.

What alloy and sized opening wire mesh are we talking about when it comes to the wire mesh option? Would we be talking stainless steel? Something like the 100 x 100 mesh stainless steel 304 thats available here: http://www.bwire.com A pie tin? Those things are so cheaply made - I don't see that standing the test of time!

 

[mjac]

Bill,
Do you think a SWR meter might be available? I am hoping I might have something up and running to check.

 

[mpinco]

.....A ground plane is absolutely defined as part of an antenna system for most common vehicular antennas. The exception might be the half-wave mobile antennas sold as "no ground plane required", but, even those have been optimized to work when a vehicle IS under the antenna. .....

The old DC vs. RF ground concept that many struggle with. The mobile vertical is basically 1/2 a dipole. A monopole. It is up to you to supply the other side of the dipole with vehicle surface or other "planes". I'm working through that now with my LR4 which has a glass top. The glass is embedded with metal for sun shielding but it is not a good "plane". Recently added a roof rack so need to construct a good RF ground to create the other half of the dipole.

 

[Hilldweller]

Bill,
Do you think a SWR meter might be available? I am hoping I might have something up and running to check.

I almost always have one in the Jeep.

 

[mjac]

Good deal!

Sent from my XT1254 using Tapatalk

 

[DaveInDenver]

What alloy and sized opening wire mesh are we talking about when it comes to the wire mesh option? Would we be talking stainless steel? Something like the 100 x 100 mesh stainless steel 304 thats available here: http://www.bwire.com A pie tin? Those things are so cheaply made - I don't see that standing the test of time!

Just needs to be conductive and the mesh not too large, but the best will be copper or aluminum and for 70cm I'd pick an opening of 10mm or smaller (tighter is better) but it would be less critical for 2m. A good, cheap material is aluminum screen door fabric if you can find the raw stuff that's not painted or coated. A couple of layers of that would be an excellent ground plane.

Just to make a point, you only technically need one radial to make a counterpoise (e.g. just making a dipole) and the more you use the better it will work up to the point that it's a continuous plane (e.g. sheet metal). So there's a point of diminishing returns - 1 works, 4 works fine, 8 better, 16 is excellent and more isn't going to start not making much difference with each additional one.

So woven mesh is treated like a shielding cloth where you analyze the aperture for effectiveness. Judging effectiveness is at first just making a good coupling and feedpoint impedance. As you start to increase the number of radials you get a cleaner pattern free of effects due to an imperfect ground.

Thus as you tighten up the weaved pattern it begins to effectively appear to the RF energy as solid metal at some point. With 2m being relatively long wavelength the opening (aperture) can be fairly large (say 100mm or even looser, 2 or 3 cm) and the waves can't tell there's any space between the threads. As you go up in frequency you have to tighten up for this to be true. For microwaves the fabric looks like regular clothes fabric it's so fine and tight. Eventually the necessary weave needs to be so tight that you are forced into using sheets and foil practically speaking.