Antenna advice

[kwallace21]

Hi folks,
Have a Mitex General 5 watt radio which I am connecting to my Autocom with a PTT and mounting the radio under the seat of my 1150 GSA.
The antenna unscrews and I have bought a length of mini co axial cable and SMA connectors from Maplin to mount the antenna on the side of my topbox.
Anywhere upright will do.
Mitex say that extending the original antenna is no problem and doesn't need to be ground planed yet another company has said it must be ground planed.
Does anyone know for sure. If I mount it on a section of the metal top box plate will that help?
Wondering if lying flat under the seat will give me enough range.

cheers
Kev

 

[Bumpkin]

Mitex say that extending the original antenna is no problem and doesn't need to be ground planed yet another company has said it must be ground planed.

I would be inclined to go with the manufacturer. I can't see how the included antenna could be ground-planed on a hand-held. So stands to reason that they are GPI and can be mounted anywhere convenient so long as the cable run doesn't result in significant losses.

Wondering if lying flat under the seat will give me enough range.

That will reduce the range to a few hundred yards in my experience, the antenna needs to be upright.

What frequency is the radio? VHF or UHF? If the latter and you're running on PMR bands then the Bikers Oracle antenna kit might be worth a look.

 

[Kritou]

Don't know anything about Mitex but somehandhelds have a metal chassis (ex A80) that provide a ground plane in rubber ducky mode

Have you considered a dipole antenna (they do not require a GP, would be about 20cms long for UK PMR and usually come with an adhesive backing that allows them to attach to the inside of your screen)?

 

[Sumprat]

Don't know anything about Mitex but somehandhelds have a metal chassis (ex A80) that provide a ground plane in rubber ducky mode

Have you considered a dipole antenna (they do not require a GP, would be about 20cms long for UK PMR and usually come with an adhesive backing that allows them to attach to the inside of your screen)?

Even if a hand help radio doesn't have a metal chassis, the holder will act as some sort of ground plane.

Whether it needs one or not really depends on what wave length configuration the antenna is.

Can't remember the exact details but a 1/4 wave antenna needs a ground plane. I think a 5/8 wave or two times 5/8 wave doesn't and a 7/8 wave does.

I'll assume the radio in question is UHF and probably near 400 Mhz. In this case the dipole will be about 30 to 35 cms long as each leg of the dipole should be a quarter wave length, thus making a half wave dipole. These are easy enough to make yourself, plenty of resources on the net.

The best method of gaining distance is height. If you could make (or buy the dipole) and mount it on some sort of mast above your head height that would be a great improvement. A thin plastic pipe with the antenna inside at the top would suffice.

 

[Kritou]

Hi folks,
Have a Mitex General 5 watt radio which I am connecting to my Autocom with a PTT and mounting the radio under the seat of my 1150 GSA.
The antenna unscrews and I have bought a length of mini co axial cable and SMA connectors from Maplin to mount the antenna on the side of my topbox.
Anywhere upright will do.
Mitex say that extending the original antenna is no problem and doesn't need to be ground planed yet another company has said it must be ground planed.
Does anyone know for sure. If I mount it on a section of the metal top box plate will that help?
Wondering if lying flat under the seat will give me enough range.

cheers
Kev

I'm not using my dipole antenna at the moment so if you want to try it out I'll stick it in the post. The feed is only about 1 metre in length so you may have to use your mini coax to extend it if you want to have the radio under the seat and the antenna elsewhere

Mounting it as suggested in a plastic pipe is a good idea as it needs to be away from the metal mass of the bike - otherwise the RF will take the line of least resistance and dissipate itself into the frame etc (giving an unbelieveably low SWR and delusions of being able to talk to the moon!)

pm your address if interested

 

[kwallace21]

Dipole

Hi there,
thank you for the offer. I think I will try the extension cable I have and see if it works first.
If not I will give you a shout and take you up on your offer.
many thanks

Kev

I'm not using my dipole antenna at the moment so if you want to try it out I'll stick it in the post. The feed is only about 1 metre in length so you may have to use your mini coax to extend it if you want to have the radio under the seat and the antenna elsewhere

Mounting it as suggested in a plastic pipe is a good idea as it needs to be away from the metal mass of the bike - otherwise the RF will take the line of least resistance and dissipate itself into the frame etc (giving an unbelieveably low SWR and delusions of being able to talk to the moon!)

pm your address if interested

 

[Boon]

Sticking a little UHF antenna on a metal topbox will give you plenty of counterpoise..........this is a good antenna site,the radiation pattern will elongate over the counterpoise so a centre fitting is technically more efficient/omnidirectional but in practice you wont loose much by mounting it to one side.

http://www.moonraker.eu/Amateur-Rad...Tri-Band/MR700-270-38th-THREAD-MOBILE-ANTENNA


http://www.moonraker.eu/Mobile-Moun...NAIL-S-MOUNT-FOR-DIRECT-MOUNT-WITH-38-FITTING



dual band antenna and mount for £14

or just buy a whip and 3/8 ths base and bingo .......an antenna and mount for less than £10