• Effective immediately we will be deleting, without notice, any negative threads or posts that deal with the use of encryption and streaming of scanner audio.

    We've noticed a huge increase in rants and negative posts that revolve around agencies going to encryption due to the broadcasting of scanner audio on the internet. It's now worn out and continues to be the same recycled rants. These rants hijack the threads and derail the conversation. They no longer have a place anywhere on this forum other than in the designated threads in the Rants forum in the Tavern.

    If you violate these guidelines your post will be deleted without notice and an infraction will be issued. We are not against discussion of this issue. You just need to do it in the right place. For example:
    https://forums.radioreference.com/rants/224104-official-thread-live-audio-feeds-scanners-wait-encryption.html

No ground plane mobile antenna

Status
Not open for further replies.

sparks40

Member
Joined
Jan 4, 2009
Messages
218
Location
Illinois
Hello all...I was wondering if someone could point me towards a manufacturer that sells a 2M/70cm whip that does NOT require a ground plane to work. I want to have a permanently mounted antenna on my truck, but due to present circumstances, the only feasible option is a stake pocket mount, which offers next to nothing in regard to a ground plane.

I currently have a 1/4 wave whip mounted there, but it's only good for 10 watts before the swr jumps up due to the lack of a proper ground plane. The only other question i have would be regarding the whip length. In my present setup, would it do me any good at all to go with something taller, like a 5/8 or 1/2 wave, or is a no ground plane antenna my best option here?
 

N4KVE

Member
Joined
Mar 1, 2003
Messages
3,015
Location
PALM BEACH, FLORIDA
Most mobile antennas do not require a ground plane. Look at all the magnetic mounts that are used. If you look in a HRO oe AES catalog at the Diamond section, only a few antennas listed require a ground plane. I have been using the same antenna for years with a magnetic mount & thick vinyl to not scratch the paint on the car, & only recently installed it with & trunk lip mount with a good ground, & no difference in performance. I still can get into repeaters 60 miles south of me. GARY N4KVE
 

LtDoc

Member
Joined
Dec 4, 2006
Messages
2,145
Location
Oklahoma
That stake-pocket mounting for a VHF antenna isn't going to be the best in the world, but it can certainly be the best for you at this time. It has nothing to do with having or not having a "groundplane" (actually, that 'groundplane' is the other half of the antenna). It does have a 'groundplane', by the way, it's the metal of the truck. It's a matter of antennas wanting to be -above- metal, and not liking to be -beside- metal (the cab). It would make a difference if that antenna were on top of the cab.
A 5/8 wave antenna will make a difference, even if were mounted in the same place as your present antenna. I can't say how much of a difference, but it would be noticeable. It would also benefit from being on top of the cab.
All antennas have two 'parts', or a 'groundplane', or a counterpoise, it's 'other half', or whatever you want to call it. If there aren't two 'terminals/connections', then there's no current flow, which means no completed circuit, which means no antenna. That 'other half' may not be apparent, but it's there. Most of the so called 'no groundplane' antennas use the feed line as it's 'other half'. Sound odd? Probably, but it's a fact. It also means that the 'other half' also radiates, just like the 'whip' part does. So, there can be disadvantages to it, as in how that feed line is run can make a big difference.
[All RF is an alternating current. That means that the (+) and (-) 'terminals switch every half of a cycle. So, during half of the cycle that 'whip' is the 'ground' and the 'gound' part is the part that's doing the radiating. 'Nuther odd thought, huh? Oh well, all this stff is a bit odd, right?? ;)
Have fun...
- 'Doc
 

W2NJS

Member
Joined
Mar 27, 2006
Messages
1,934
Location
Washington DC
The stake that you're using serves as the ground, although it's a poor ground plane, right now, so the stake and truck bed serves as the other quarter-wave of the quarter-wave antenna. And the SWR is the same ratio in a system whether you're running one, ten, or one hundred watts. If you want to get a better match then MFJ makes an inexpensive VHF antenna tuner which I think can be used mobile.
 

KC0KM

Member
Joined
Dec 19, 2002
Messages
278
Location
Kansas City (Raytown) MO
Although it may not be related, on my father's van, a Chevy Lumina AVP, is all fiberglass, and there is no way to mount a magnetic mount antenna. I learned that with a mag-mount, that the vehicle it's self is the ground plane. So (in various of versions) came up with a mobile magnetic ground plane.

I have taken a piece of sheet metal, a heating register/run plug. I then had welded on four pieces of heavy wire (coat hangers) cut to about 15 inches or so, on the corners. I then screwed in suction cups, which then sit on the van. I have another one (I made two is last time), and my father is using it for his HT to get better into the repeater (he used it for the first time last week, and it worked like a charm).
 

prcguy

Member
Joined
Jun 30, 2006
Messages
7,818
Location
So Cal - Richardson, TX - Tewksbury, MA
Most no ground plane antennas are a 1/2 wave end fed with a matching circuit, basically the same as a J-pole but with an LC or combination with a transformer instead of the 1/4 stub matching.

When properly designed there is no feedline radiation and the feedline is not considered part of the antenna. The end result is about the same radiation pattern and gain as a center fed dipole.

If you terminate the end of some coax with a 1/4 wave, 5/8 or anything other than a 1/2 wave and no ground plane, then then coax will want want to have RF current flowing and it will radiate.

Most VHF or UHF antennas in a truck bed stake pocket should tune and work ok. I have an NMO mount on an L bracket on my truck bed rail that serves the same purpose and antennas that were tuned on a roof mount have slightly high VSWR on the L bracket due to the extra whip capacitance to ground when tuned on the roof but when tuned on the bracket they achieve low VSWR and work fine.
prcguy

That stake-pocket mounting for a VHF antenna isn't going to be the best in the world, but it can certainly be the best for you at this time. It has nothing to do with having or not having a "groundplane" (actually, that 'groundplane' is the other half of the antenna). It does have a 'groundplane', by the way, it's the metal of the truck. It's a matter of antennas wanting to be -above- metal, and not liking to be -beside- metal (the cab). It would make a difference if that antenna were on top of the cab.
A 5/8 wave antenna will make a difference, even if were mounted in the same place as your present antenna. I can't say how much of a difference, but it would be noticeable. It would also benefit from being on top of the cab.
All antennas have two 'parts', or a 'groundplane', or a counterpoise, it's 'other half', or whatever you want to call it. If there aren't two 'terminals/connections', then there's no current flow, which means no completed circuit, which means no antenna. That 'other half' may not be apparent, but it's there. Most of the so called 'no groundplane' antennas use the feed line as it's 'other half'. Sound odd? Probably, but it's a fact. It also means that the 'other half' also radiates, just like the 'whip' part does. So, there can be disadvantages to it, as in how that feed line is run can make a big difference.
[All RF is an alternating current. That means that the (+) and (-) 'terminals switch every half of a cycle. So, during half of the cycle that 'whip' is the 'ground' and the 'gound' part is the part that's doing the radiating. 'Nuther odd thought, huh? Oh well, all this stff is a bit odd, right?? ;)
Have fun...
- 'Doc
 
Last edited:

prcguy

Member
Joined
Jun 30, 2006
Messages
7,818
Location
So Cal - Richardson, TX - Tewksbury, MA
I've seen transformer and autoformer configurations where the low impedance end is connected to the shield and center conductor to the first tap and the high impedance end cap coupled to the radiator. The transformers are like a 9:1 ratio or higher and the PAR end fed series would be similar.

The dual winding transformer types would have one end of the high impedance side connected to the shield and I've also seen some odd setups like the A99 where they have their own formula for matching with a transformer and capacitors.
prcguy


prcguy,
And what is that transformer connected to??
- 'Doc
 

woodylarkin

Member
Premium Subscriber
Joined
May 14, 2006
Messages
5
Location
Indianapolis, IN
No Ground Plane Mobile Antenna

The Diamond NR770HNMO is one good example of a no ground plane antenna. It is for 2 meter, 70 cm. I have one mounted on the left side of the hood on my Toyota Tundra. It is mounted using a Diamond K400SNMO mount. This mount clamps to the edge of the hood, trunk, door, etc. It can be attached to act as a ground or not depending on what type of antenna you are using. Another advantage of no ground plane is that there is no need to damage the paint on your vehicle. This antenna also has a fold-over feature if you need it.
 

woodylarkin

Member
Premium Subscriber
Joined
May 14, 2006
Messages
5
Location
Indianapolis, IN
True, but if a ground is required when using a clamp on mount, the screws on the uderside of the (hood, trunk, door, etc.) must be tightened to go through the paint to contact bare metal; if a no ground plane antenna is used, a small aluminum strip is used over the screws to clamp the mount.
 

LtDoc

Member
Joined
Dec 4, 2006
Messages
2,145
Location
Oklahoma
... and those screws are typically on the 'underside' of the body panel the mount is attached to. The baring(sp) surface on the top side of that body panel can be 'padded' to prevent any marring. The biggest problem I have with any of the 'lip mounts' is that the feed line has to make a very sharp bend to get under that panel. That is going to limit the size of the coax used with that mount, and with the sealing the mount might interfere with.
I've found that for my particular purposes just drilling the required hole isn't a big deal. YMMV naturally.
- 'Doc


(Have I ever had problems with those holes? Of course I have. If I don't do it right, I usually have to do it over again, or fix what I shouldn't have done to start with. Those holes have never made any appreciable difference in trade-in value. If a salesman starts in on that nonsense, I find another salesman. Simple. Then again, I (and the bank) have owned the vehicles I've drilled holes in. That can make a difference.)
 

woodylarkin

Member
Premium Subscriber
Joined
May 14, 2006
Messages
5
Location
Indianapolis, IN
Those are valid points, doc.
The Diamond mounts come with RG 316 cable which is very thin, 50 ohms, and temperature resistant to 200 degrees. It was fairly easy to install and pass through the firewall along with the power cable from battery for radio. I did not encounter any problems with kinks.
 

Anderegg

Enter text in this field
Premium Subscriber
Joined
Mar 7, 2010
Messages
1,589
Location
San Diego
Old thread, but it has elements that are similar to my question.

I've got a low band whip mounted on a black painted L bracket on my quarter panel. For RX ONLY, do I need to crape away the black paint where the NMO mounts and the screws bolt to the car to get (ground) optimum reception?
 

krokus

Member
Premium Subscriber
Joined
Jun 9, 2006
Messages
3,775
Location
Southeastern Michigan
Old thread, but it has elements that are similar to my question.

I've got a low band whip mounted on a black painted L bracket on my quarter panel. For RX ONLY, do I need to crape away the black paint where the NMO mounts and the screws bolt to the car to get (ground) optimum reception?
Optimum? Yes. Will it work, without removing paint? Probably.

Sent via Tapatalk
 
Status
Not open for further replies.
Top