No ground plane antenna to improve reception?

[DanLP456]

So I listen to my SDS-100 at work and the mobile antenna sits on my desk with no ground plane. I’m currently using an EM Wave EM-M43002 (EM Wave EM-M43002 Tri-Band 150-162/450-490/763-870 MHz Mobile Antenna - 17.7 in - NMO - Spring Base) and it says ground plane required. I listen to a 700mhz trunked system mostly but also a little VHF and UHF and the reception seems fine. I’m curious if my reception could potentially be improved with a no ground plane antenna such as the Browning BR-136 (Ultra Multi-Band Antenna 136-174/380-520/698-960 MHz Browning BR136). Or maybe it doesn’t matter much that I don’t actually have a ground plane? Thanks for any advice!

 

[jtwalker]

What is the EM-Wave sitting on?

 

[DanLP456]

What is the EM-Wave sitting on?

An NMO magnet mount on a wooden desk.

 

[ka3jjz]

You need to put it on something the magnet will grab onto. A large cookie sheet (the bigger the better) might be just the ticket. Move it around a bit. There may be more than one sweet spot in your place. Won't hurt anything

 

[jtwalker]

Hoping you were going to say metal desk…

Bring a metal cookie sheet from home and slip it under there and see if you observe an improvement.

Just from practicality I would say a non ground plane antenna should perform better than your current setup, but I’m not an expert.

 

[mmckenna]

An NMO magnet mount on a wooden desk.

That ain't a ground plane, unless there is metal within a few fractions of an inch under that wood.
If it is a large enough magnetic mount base, it may provide a suitable ground plane on 800MHz, but it won't on UHF or VHF.

Try putting it on a metal baking sheet, file cabinet, aluminum foil, metal screen, etc.

I'm skeptical that the Browning is actually a 'no ground plane' antenna on all those frequencies. The similar models from the major manufacturers are not sold as no ground plane antennas.

Even if they are "no ground plane", they are usually a 1/2 wave design. A 1/2 wave design has 0dB of gain without a ground plane, the same as a 1/4 wave antenna on a ground plane. The EM Wave multiband antenna is 1/4 wave on VHF and it has some actual gain on UHF and 7/800MHz with a ground plane.

I wouldn't spend money on the Browning and expect better performance than what you have now. I'd put the effort into putting a ground plane under the EM Wave and using that.

 

[prcguy]

The Browning should use a ground plane and not counting that my experience is the Browning might work a tiny bit better on VHF at the expense of a little worse on UHF. This is due to the loading coil on the EM Wave breaking up the whip to perform better at UHF but the coil has a little loss at VHF reducing its performance and the Browning does not have the coil. Hard to say what the difference is on 700/800 but I would expect the Browning to have a wider band width on 7000/800/900 from the fat base that is active on those bands.

 

[prcguy]

I see a lot of other ads for the Browning BR-136 and none of them mention "no ground plane". I suspect the Antenna Farm made a mistake.

 

[merlin]

If you understand what a ground plane is, you find it raises the gain lobe just above horizontal. This gain is what antenna makers use in their advertising.
A ground plane is not mandatory, an antenna can still be tuned to resonance without that. The gain lobe instead of being compressed above horizontal is now like a huge doughnut flat to the horizontal It will be less compared to the ground plane.
Take for example a low VHF antenna on a car rooftop. It has a better gain lobe than say the same antenna on a motocycle. the antenna still tunes but a bit longer. For receiving, the difference is hardly a 2 Db loss so you may never even notice. Why a scanner with that little whip on the back can work so well.

 

[prcguy]

If you understand what a ground plane is, you find it raises the gain lobe just above horizontal. This gain is what antenna makers use in their advertising.
A ground plane is not mandatory, an antenna can still be tuned to resonance without that. The gain lobe instead of being compressed above horizontal is now like a huge doughnut flat to the horizontal It will be less compared to the ground plane.
Take for example a low VHF antenna on a car rooftop. It has a better gain lobe than say the same antenna on a motocycle. the antenna still tunes but a bit longer. For receiving, the difference is hardly a 2 Db loss so you may never even notice. Why a scanner with that little whip on the back can work so well.

Some half wave end fed designs can operate fine without a ground plane but many try to use the coax shield as a counterpoise making it an active part of the antenna causing some RFI problems at the radio end. As mentioned a ground plane can help pull the radiation pattern towards the horizon improving coverage at a distance, otherwise a ground plane does not/should not radiate. Ground radials can also help keep RF off the coax and decouple the coax from the antenna.

Some older thoughts on 1/4 wave ground plane antennas were incorrect showing a 1/4 wave radiator, a ground plane then a "mirror image" below the ground plane and claiming it radiated similar to a 1/2 wave dipole. This is NOT true and a 1/4 wave ground plane will be about 1dB down from a 1/2 wave dipole because half the antenna (the ground plane or ground radials) do not radiate. I would think the Browning BR-136 is in this category being a 1/4 wave at VHF, 3/4 wave at UHF and a fat 1/4 wave at 700/800 sort of isolated from the whip from a discontinuity between the fat base and whip. Without a ground plane I would expect the coax shield to radiate and be an active part of the antenna.