Motorola TDN6084A antenna ground plane question

[Josh]

I've acquired a used, but nice Motorola TDN6084 VHF Fiberglass antenna... it's 20' long.

Anyhow, it didn't come with a ground radial set. So, is there a suitable alternative, or can someone give me direction on radial length and downward angle if I have to make my own?


-Josh

[psapengineer]

Josh,

It's a co-linear antenna, right? I don't remember the model number.......

It should be able to operate without the 'radials.

Otherwise,

Try about 18" at 120Deg spacing, 30 degrees away from the mast (60 deg below horizontal...)

That should be close enough.......

[Josh]

Josh,

It's a co-linear antenna, right? I don't remember the model number.......

It should be able to operate without the 'radials.

Otherwise,

Try about 18" at 120Deg spacing, 30 degrees away from the mast (60 deg below horizontal...)

That should be close enough.......

Yes, it is a colinear, but I am unsure exactly how things stack up- it isn't obvious. It only gets "5.25 db" of gain, over a half-wave, which doesn't seem like very much for its size (20') for VHF. I had a cheaper aluminum antenna boasting 6db of gain and was only 8' in height (stacked 5/8 wave antennas).... maybe it referenced a quarter wave for its gain specifications. Either way, I stood it up on a jack stand in my back yard, leaned against the garage with a short run of RG8x with better than expect results (the top 8-10 feet cleared the garage roof-line).

Thanks for the tips, similar antenna seem to show a 45* angle, I just wanted to be sure (since these are typically mounted way higher than I can gauge with a protractor!)

-Josh

[515]

I picked up a similar used antenna a few years ago. Not sure on the part number, but mine is badged "Motorola", and rated for 150-159 MHz. It was wall-mounted on the penthouse of an old hospital building that was being demolished, so there were no radials on it.

I think it's basically an RFS/Celwave PD220 series "Super Stationmaster", which do have the radials. So maybe the thing did originally come with them, but they were removed so it could be mounted on a wall.

I've got it mounted on my chimney now, and swept it with a SiteMaster, and it was fine over the 150-159 range... So it seems to be happy without them, at lease VSWR wise.