groundplane question

[af5rn]

Jon, weren't you having some problems with that setup? SWRs or reception or something? Did you ever determine what the problem was? It still seems to me that those plastique stand-offs might be a hindrance.

 

[jon_k]

Jon, weren't you having some problems with that setup? SWRs or reception or something? Did you ever determine what the problem was? It still seems to me that those plastique stand-offs might be a hindrance.

Yes. This setup did and still does have a small problem. Engine noise!

As I described in another thread, this only appeared when I connected to the stereo input of my vehicle stereo. (Scanner headphone to stereo AUX jack)

Well, with my amateur rig the noise is always there when I am RX. Friends say that they hear not a crackle or even a pop when I'm TXing, which is nice to know.

Noise is non existent when the ignition key is set to ACCESSORY with all accessories on. It's not the fuel pump or anything else. Once starting the vehicle, I get the noise. Rev the engine and noise gets louder.

Sounds like I've got a spark gap transmitter under the hood. Could be the rotor, spark plugs, or leak from plug wires. Unsure which, or how to fix. This is a 1994 chevy truck, obviously lacking all the high-tech electric ignition systems. It's all oldstyle, timing and everything.

I never tried grounding the antenna base to the battery ground post/wire. Perhaps that would cure or eliminate some RFI? Don't know, will try it on my next day off. If this this experiment has good results, then I will:

1) Ground the toolbox itself to the negative battery post (Or the cab chassis. Who knows if the truck bed is well grounded.)
2) Either A) Add an electric jumper (short wire) from toolbox metal to antenna base or B) Get metal standoffs to do the trick for me.

 

[jon_k]

ugh. dupe post.

 

[rvawatch]

As long as you aren't transmitting no interference should be caused. (If you do transmit, the scanner connected will be destroyed from the power obviously.) I'm not an expert at running multiple devices off one antenna. This should be fine though.

I have posted a similar question about this recently. Are you saying that the scanner would be destroyed by simply being hooked up to its own antenna at the same time another radio was hooked up to a separate antenna for transmitting? In my case it's only a 5 watt CB, and I know you are referring to a ham radio, but I might get one someday.. so I am curious.

Thanks

 

[jon_k]

I have posted a similar question about this recently. Are you saying that the scanner would be destroyed by simply being hooked up to its own antenna at the same time another radio was hooked up to a separate antenna for transmitting? In my case it's only a 5 watt CB, and I know you are referring to a ham radio, but I might get one someday.. so I am curious.

Thanks

Yes.

Receiver circuits in the radios are not meant for the high voltages put through the wire when a radio transmits. They are rather intended for the very low inducted power from radiowaves to amplify and receive. If you send them the powerful voltage of RF through that scanner, I'm sure it would be toast in 2-3 seconds or less. The receivers on CB radios and the sort avoid frying during transmitting because of a relay (I assume) that flips when put in transmit mode to keep it isolated from the transmit circuit.

[EDIT, READ!]
No.

I didn't read your question correctly. I thought you meant put the scanner and the C.B. on 1 antenna split on 1 feed line. That'd be bad.

You said the Scanner and CB will have separate antennas. If this is the case and CB transmits, it will not destroy the scanner. However, the scanner will have poor operation during transmit. It will desense the frontend of the scanner.

The RF from the C.B. will be so powerful that it will basically flood the VFO of the scanner to the point that it can't discern other frequencies from the C.B. frequency. It will be so powerful it will silence any other frequency to the scanner. You won't hear anything during transmit (unless you're listening to the c.b. frequency on the scanner.)

Once you unkey the CB, scanner will work again.

 

[jassing]

Sorry to jump in on an old thread.. but:

This is ___exactly__ my setup. It works wonderfuly. See attached images for reference on my setup for my scanner antenna.
<snip>Click link for OVERALL picture of the mount on the truck. http://i27.tinypic.com/jfgn6r.jpg

Emedded on the right: Closup of assembly

I was looking to mount a CB antenna to the back of the cab, exactly you have on your tool box.. at the edge, with teh antenna at the ground plane, just not on the ground plane. I was told this wouldn't result in a useful ground plane.

I was gong to mount the cb on passenger side and scanner on drivers side -- same method you used on the toolbox, same placement (i the toolbox were the cab/roof) just w/o the spacers.

So this thread actually contradicts what I gleemed from others -- your real world performance is good with this setup?

I have substantially more space at hte back of the cab for mounting than you do (older truck)

thanks
-josh

 

[W6KRU]

Sorry to jump in on an old thread.. but:



I was looking to mount a CB antenna to the back of the cab, exactly you have on your tool box.. at the edge, with teh antenna at the ground plane, just not on the ground plane. I was told this wouldn't result in a useful ground plane.

I was gong to mount the cb on passenger side and scanner on drivers side -- same method you used on the toolbox, same placement (i the toolbox were the cab/roof) just w/o the spacers.

So this thread actually contradicts what I gleemed from others -- your real world performance is good with this setup?

I have substantially more space at hte back of the cab for mounting than you do (older truck)

thanks
-josh

Since jon hasn't posted since August-2008, you probably won't get an answer from him. That setup will probably work but it will be far from optimum. It will work better with a 1/2 wave antenna but still not optimum.

 

[snakecharmer]

Sorry to jump in on an old thread.. but:



I was looking to mount a CB antenna to the back of the cab, exactly you have on your tool box.. at the edge, with teh antenna at the ground plane, just not on the ground plane. I was told this wouldn't result in a useful ground plane.

I was gong to mount the cb on passenger side and scanner on drivers side -- same method you used on the toolbox, same placement (i the toolbox were the cab/roof) just w/o the spacers.

So this thread actually contradicts what I gleemed from others -- your real world performance is good with this setup?

I have substantially more space at hte back of the cab for mounting than you do (older truck)

thanks
-josh

Wow this is an old thread! I guess I never updated with what I ended up doing. I tried a mirror mount setup like in that picture bolted to the side of the box and it didnt work too well. That is not my truck but setup was similar. I then bolted a couple pieces of steel plate to the top of my aluminum tool box so that I had a place to stick mag mounts. It worked marginally better. Shortly after that, I purchased a fiberglass camper shell so I needed to relocate everything. I bit the bullet and drilled a hole and installed an NMO mount just in front of the third brake light and installed the 2m antenna there. I then installed another NMO on a fender bracket on the driver side of the hood directly across from the regular radio antenna. I ended up ditching the CB and second scanner all together. The difference in performance was night and day to say the least. So in my experience the tool box is a last resort. As for the hole in the roof, I installed a black plastic NMO cap when I traded it in last year and they probably thought it was an XM antenna or something.

Here are the only real pictures I have but you can see both antennas. And here is my dash install as well. I since shortly after replaced the Yaesu with an Icom with green backlighting bucause my OCD couldnt deal with one yellow backlight.

 

[jassing]

Since jon hasn't posted since August-2008, you probably won't get an answer from him.

Good point...

That setup will probably work but it will be far from optimum. It will work better with a 1/2 wave antenna but still not optimum.

There's no way to be "optimum" with multiple radios. "anything will work" -- but I want more than crap, understanding I'll never get optimum.

thanks
-j

 

[W6KRU]

There's no way to be "optimum" with multiple radios. "anything will work" -- but I want more than crap, understanding I'll never get optimum.

thanks
-j

Optimum is doing the best you can with the restrictions you have to work with. You seem to be looking for a justification to mount antenna on the back of your cab. If I was an antenna installer, I might just mount the antennas the way you want them and send you on your way. I would have done the best job I could taking the customers wishes into consideration.

If some one else came into the shop and was not opposed to me drilling holes in the cab of his truck, I would mount both antennas on top of his cab and send him on his way.

The setup with the antennas on top of the cab will work a lot better but both installs are optimum.

You have to figure out what you want and go with it. If you have to mount them on the side of the cab, go for it. It will work like crap but if you can't provide a ground plane then deal with it the best way you can and go for it.

You should not use an antenna that requires a ground plane for proper function so that means you will be restricted to a 1/2 wave antenna because a 1/4 or 5/8 wave both require a ground plane. You are going to have to compromise somehow. Plenty of police cars that had vhf-low band radios had 1/4 wave antennas mounted on left rear fenders which was a poor ground plane. That was a compromise that was made to work.

My optimum is not going to necessarily match your optimum. I would prefer a mag mount on the roof over mounting on the side of the cab. That would cause a headache due to the routing of the coax into the cab but it would be my compromise if I couldn't drill holes in the roof.

You just can't change what a ground plane is or isn't.

 

[jassing]

Optimum is doing the best you can with the restrictions you have to work with. You seem to be looking for a justification to mount antenna on the back of your cab. If I was an antenna installer, I might just mount the antennas the way you want them and send you on your way. I would have done the best job I could taking the customers wishes into consideration.

I have no problem drilling holes, the problem is the height restrictions I have -- A rack over the cab yields very little space there.... for UHF it seems "higher is better" so mounting on the back of the cab is better than mounting on the hood. I get a lot of EFI from the engine; so I'm trying to avoid mounting on the hood..

If mounting on the toolbox as in the picture is better than mounting on the cab; then I'll mount there -- I don't understand why the toolbox is a better ground plane than the cab hood.
I'm trying to understand what makes a good ground plane when the optimal ground plane is not available.

If some one else came into the shop and was not opposed to me drilling holes in the cab of his truck, I would mount both antennas on top of his cab and send him on his way.

Even if I could mount a 3 or 4' antenna on the roof, it would require me taking the antenna off driving down some streets with trees... it'd just put the antenna too tall for practical daily use.

The setup with the antennas on top of the cab will work a lot better but both installs are optimum.

Point taken.

You have to figure out what you want and go with it. If you have to mount them on the side of the cab, go for it. It will work like crap but if you can't provide a ground plane then deal with it the best way you can and go for it.

Not side, back. Just like the picture shows on the back of the toolbox -- just up another 2'

thanks. I admit I don't fully understand proper ground planes -- which is why I'm asking to try to understand it so I can adapt it.

It almost seems like I should get a chunk of sheet metal mount it high above the tool box and mount the antennas there...

Appreciate your advice, and points are well taken.

 

[W6KRU]

If your only problem with a roof mount is whacking trees, then why not use a short antenna on the roof? I would much prefer a short antenna on the roof over a 4' antenna mounted on the back of the cab. A Larsen 150/450/800 is only 19" and will probably have more clearance than a 4 footer on the back of the cab. The Larsen is a quality antenna that will probably outperform any fiberglass antenna on the market and doesn't cost a lot either.

 

[jassing]

If your only problem with a roof mount is whacking trees, then why not use a short antenna on the roof? I would much prefer a short antenna on the roof over a 4' antenna mounted on the back of the cab. A Larsen 150/450/800 is only 19" and will probably have more clearance than a 4 footer on the back of the cab. The Larsen is a quality antenna that will probably outperform any fiberglass antenna on the market and doesn't cost a lot either.

Thanks; but "if I could mount a tall antenna...." -- roof rack is in the way.
I guess I could mount them on the toolbox with some quick disconnects if that'd be better... I was going on "taller is better" theory -- but if that isn't the case -- I'll drill up the toolbox -- beats cutting a hole in the body anyway.

 

[W6KRU]

Thanks; but "if I could mount a tall antenna...." -- roof rack is in the way.
I guess I could mount them on the toolbox with some quick disconnects if that'd be better... I was going on "taller is better" theory -- but if that isn't the case -- I'll drill up the toolbox -- beats cutting a hole in the body anyway.

OK. It sounds like you have to make a compromise. If you mount the antenna to the toolbox, the cab will shield the antenna from signals coming from the front of the truck and it will be less sensitive from that direction. You have to live with it and it's your decision to make.

 

[jassing]

OK. It sounds like you have to make a compromise. If you mount the antenna to the toolbox, the cab will shield the antenna from signals coming from the front of the truck and it will be less sensitive from that direction. You have to live with it and it's your decision to make.

Thanks DDan. that's exactly it -- I have to compromise, I can't use "the optimal"... However, i was hoping that someone ( with more knowledge than I have) would say one way is better than the other; not just "you're not doing it on the roof, so whatever you do sucks" I was hoping for something like "option A sucks the least". I don't know if mounting it higher w/o a ground plane OR mounting it in a blocked location but on a (sort of) ground plane sucks less than the other. As I read all the posts, faqs, etc -- the toolbox will not provide a proper ground plane anyway -- it's not big enough.

Thanks for your input tho -- I appreciate your time. I'll take the info I have and decide where to drill the holes ...

-j

 

[K2theFEA]

Hi guys,

Hoping for some guidance/suggestions on antennas, placement and mounting. I have a 2013 Kia Sorento and the entire roof is a panoramic moonroof i.e. all glass. Due to the shape of the hood and hatch I think my mounting options are severely limited. I have the factory roof rails and an aftermarket Thule Aeroblade crossbars. For the time being I am only interested in scanning. I'll eventually want to get into CB radio. For now, I'm mainly scanning for VHF low 39-59 MHz. My garage, that I park in everyday, won't support an antenna taller than 18 inches. What do I do? Am I SOL? Here is a picture of the roof (not my exact car but you get the point):

https://s-media-cache-ak0.pinimg.com/736x/35/5c/41/355c413b315a9a3a7722cbbb09bf0e8a.jpg

Hope you guys can give me some good tips. I am open to entertaining any suggestions and then I'll whittle them down to my favorite one. I am not adverse to drilling holes on the side, back or roof. Just want to know what is the best technical, cosmetic and practical fit.

Thanks,

 

[jassing]

I would think a magnetic mount would be best.
I had very good luck with a little magnetic mount that was less than 16" and I would just toss the antenna wherever and run the coax thru a window. Worked better than the scanners own antenna.
Once you get into transmitting, the ground plane will become an issue, but they do make "no ground plane" antennas. Whips mounted at the bumper or side of car work well and are very forgiving to hitting things. A hood mount, either side or forward, is another option. Since "size matters" when using a cb antenna you might consider a nice solid mount and a quick-disconnect so you can just pull it off prior to getting into your garage. (or parking on the street)

 

[K2theFEA]

Glad to help.




Understandable for one hole. I am considering 1 hole in my roof as well. I'd put it in the center horizontal, but vertically it would be further near my brake light as well.


I have also seen hood mounts that are made for specific trucks. You may see if you can find one made for your truck specifically.



We may have differing priorities and interest in the radio hobby which may conflict with each other.All I can share is what I would do with your truck, and why:
ROOF: The hood is the #1 best spot, and in my mind thats for the transmitter. Mainly because transmitted signals go out further with a proper ground plane. After all, don't you want to be able to reach those distant repeaters on the other side of town? (My biggest pet peeve is to be able to hear a repeater, but not be able to Tx to it. I try to do anything (height/groundplane) to increase my chances.) I also like to at least listen to repeaters as distant as possible.

To add to my reasoning, amateur radio repeaters (and your transmitter) run on very low power output when you compare it to the hundreds of watts your commercial Police/Fire repeaters are pushing. So you earn more with a ground plane here in my opinion. You might pick up Police with a twist-tie made into antenna buried 6 feet under concrete with rebar. Unfortunately the amateur systems aren't as powerful with their output, and your 2 meter rig probably does 50watts max. Give it the height and ground plane advantage.

HOOD / BED
The next best option with the best ground plane area will be your hood. The antenna will be likely in the top left corner of your hood by the drivers area. Not the best ground plane, but OK.

I can't tell you what to put here.

• Do you value performance on 150/440mhz?
• Do you value performance on 800mhz?

Pick one that has higher value and put it on the hood. It will gain the benefit of the ground plane. It just depends on which priority you want for which antenna.

Pro TIP: For all your antenna mounts, purchase the same type of antenna mount types. That way you can move antennas among the mounts. The antennas and each mount will be interchangeable this way. If your priorities change, you can just unscrew an antenna and move it to another mount. I've made this decision on my vehicle and have standardized in NMO. I'm happy with the standardization.

Pro TIP 2: Use the same coax connector on the end for your radios. Standardize on all BNC end connectors, or all PL-259. That way any antenna wire can be used with any radios. (I'd do all BNC since it's a small connector. For the HAM radio you can get BNC to PL-259 to connect to your radio. Your preference. This is so you can interchangeably change antennas on your radios.) This will just simplify interchangeability and makes things simple for new equipment addition in the future.



I use an Austin Spectra for my scanning needs. I use an Comet SBB-7 2 meter/70cm antenna for amateur use. I'm happy with both.

These are my first mobile antennas. I've not been around long enough to start making recommendation's for other peoples rigs. However, 3 of my HAM friends purchased the Comet SBB-7 the same day after I purchased mine at the Hamcom here (and one of the operators who purchased has been an operator for 7 years, general.)




Building a ground plane with sheet metal is acceptable. Aluminum is an excellent conductor. When you get /really/ specific the ground plane will need to be a specific length out from the center of the antenna base. You will need to find a site with a list or the equations to calculate proper length of your ground plane for the frequency your running. (In the perfect world they say an infinite ground plane is the best. This is never possible though unless you have property rights to a place like Earth made out of pure copper. I'm also sure you appreciate some space in the bed.



Well an proper ground plane would be a solid circular sheet of metal with a length calculated base on the center frequency of the antenna tuning (90 degress from the whip). Of course, those guys with a huge HF antenna towers usually bury steel rods of the calculated length (as many as they can muster) under the ground in their back yard. You can do the same thing with metal rods. You would add as many as you can (or ideally a flat circular peice of sheet metal) around the base of the antenna. Again you will need to calculate how far out the metal reaches for the center frequency your antenna is tuned for.

Again, for the bed you may not even bother adding a ground plane. It's just something to do for added performance if you happen to have one in a suitable location for antenna placement. Myself, I don't think I'd fabricate a ground plane if I didn't have one readily available.



Having a dedicated 800mhz isn't a bad thing. But running two scanners off one antenna is fine.

Running both scanners off the same antenna has been done before plenty of times. Some people just get a T connector and do it that way. Other people get isolator devices to isolate the two scanners.

The scanners shouldn't interfere with each other in my opinion. You may get a birdie or two from internal interference from the VFO's but this should be rare and there's only about 4-5 birdie frequencies in the whole scanner. The birdies won't damage anything.

As long as you aren't transmitting no interference should be caused. (If you do transmit, the scanner connected will be destroyed from the power obviously.) I'm not an expert at running multiple devices off one antenna. This should be fine though.

Thanks for all the indpeth feedback you post! Very helpful. Quick question, do you like the performance of the Austin Spectra in the 40-50 MHz range?

Thanks,

 

[zues2054]

Ground Plane

Great topic..
I found this thread as I was doing research on Transponder antenna installation on my helicopter. my question is:
Does the antenna have to be physically attached to the ground plane? In my best installation location, the antenna will be attached to a aluminum plate approx 6x6" that is mounted to the helicopters frame. This plate is approx. 18" below the aluminum hull (engine etc. keeps me from mounting directly to hull). Transponder operates 960.0-1164.0 mHz.
Thanks for your input.

 

[prcguy]

A 6X6" plate is plenty big enough for an effective ground plane in the 960 to 1164MHz range. Ideally the antenna would sit in the middle of the plate with the plate having a very short and direct connection to the shield of the antenna.

The typical little whips used for DME and similar at those frequencies have a integral mount with a TNC connector, you just drill a hole in a metal sheet and the mount will ground properly. Installing an antenna like this usually requires a licensed aircraft mechanic/tech.
prcguy

Great topic..
I found this thread as I was doing research on Transponder antenna installation on my helicopter. my question is:
Does the antenna have to be physically attached to the ground plane? In my best installation location, the antenna will be attached to a aluminum plate approx 6x6" that is mounted to the helicopters frame. This plate is approx. 18" below the aluminum hull (engine etc. keeps me from mounting directly to hull). Transponder operates 960.0-1164.0 mHz.
Thanks for your input.