Dumpster Dive antenna ID

[CbusRog]

I'm trying to identify this antenna. A friend of mine rescued it from the dumpster where he works (there were six of them, and I got one). He's an electrical engineer and holds an Extra Class license, yet he didn't know right off what it was, other than a VHF-UHF multi-band (I suspect he left identification up to me as an exercise). He knows I'm into scanning and have the ability to put an antenna up high (35' over local terrain), and he thought it might be a good starter base-antenna for me. There are no numbers or identifying marks of any kind. The longest element measures 69.5", the second longest measures 48", and the short element measures 16.5". The three horizontal radials measure 77.5" each. (The center element and radials are adjustable; the lengths are how I found them.) I did the math on the elements for 1/4 wave and 1/2 wave, and nothing fell within any common bands. I then calculated 5/8 wave, and the two shorter elements landed mid-band for 70cm and 2m. The longest element came close to mid-band for FM broadcast at 5/8 wave. ???

The connector is a N-type with a BNC adapter. I connected my GRE PSR-500 with a 6', 50 ohm coax, at ground level, but did not notice any improvement in reception on any bands, and in some cases, worse than my Diamond RH77CA. Of course again, this was not up high, but at ground level, and inside.

The antenna was free, so if it doesn't work out for scanning, it's no big deal. I'm just wondering if it's worth mounting up high.

 

[jon_k]

Looks like a Jpole but I didn't know they benefit from groundplane.

Plus the design is incorrect (the dimension length and gap of J). For Jpoles the scale is more like this:

|````
|````
|```|
|```|
|_|_|
|````
|````---- < feed

Where:
| = 70cm

Where:
|
|
| = 2 meter

Where:
|
|
|
|
| = Driven

 

[btritch]

I used to have one JUST LIKE THAT..Same identical thing until the Twister of 08 got ahold of it and tore the center from the ground plane, , It's one of the older rat shack bases I think...I got mine used so not real sure..

Not real good on the 400 MHZ range though, 'SPECIALLY bad on the 800 MHZ...or 900 MHZ range...

 

[lebrunmn]

That's an old Radio Shack 20-014... I used to have one: great with VHF, not so hot in the 800MHz range, though.

Regards,

 

[blueangel-eric]

boy that's a nice find!!!! i never find antennas in the dumpster.
but recycling places is a good place to look if they let you.
Eric Burris

 

[CbusRog]

That's an old Radio Shack 20-014... I used to have one: great with VHF, not so hot in the 800MHz range, though.

Regards,

Yup, that seems to be it. (I Googled the RS part number - pictures, reviews, etc.) Thanks!

 

[217]

Rat Shack 20-014

I bought one of these used in 93. Did not find it very useful for 800's cellular. It just collected dust until two years ago when I made a j-pole from it for 161.000 Mhz. 1st pic is the day i made it. Second is after recalculating and fine tuning. Antenna picks up signals from 100 miles on good days.

 

[kb2vxa]

It's a tri band quarter wave ground plane and your math is right. Never mind the 1/2 or 5/8 wave bit, the feed point impedance is all wrong and would require a matching network for each band. 3/4 wave also gives you a 50 ohm impedance BTW so now you have to figure out what you want to do with it, "free" gives you a lot of latitude.