I'm looking to build a 1/4 wave 11 meter CB Ground Plane antenna, like the one Radio Shack used to sell. Does anyone have the dimensions for the radiator and radial lengths? Thanks!
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Dimensions for 1/4 wave CB Ground Plane?
- Thread starter TheSpaceMan
- Start date
Try this using 4 or more stainless steel 102" whips, a mirror mount L-bracket, and one of more hubs from an A99. I have several homemade hub and I also make one that only uses 1, 2, or three slanted down radials. The more radials I use the better the antenna seems to work at my location.
You don't need the pipe attached to the side of the antenna, just tape the coax close to the mast. Works better for me than you might expect. I'm thinking of building one and adding it to my list of antennas to compare, and I'll get it up about 35' feet, and post my results here on WWRF.
Good luck, and keep us posted.
Marconi's is of sturdier materials than mine, but it can be done with wire, a fishing pole, and some PVC.
The vertical starts out around 9', and is trimmed down until the SWR is good.
The radials are roughly 5% longer than the vertical.
The vertical starts out around 9', and is trimmed down until the SWR is good.
The radials are roughly 5% longer than the vertical.
B
BOOTY MONSTER
Guest
Awesome. That Archer 21-901 Ground Plane was the exact antenna that I was thinking about! Interestingly, in the picture it appears that the radials go straight out and are not sloping downward like most ground planes! (The old Lafayette CB ground plane had sloping radials). Perhaps the fact that the elements are 108 inches might have something to do with it? Hmmmm.
Horizontal radials or sloping radials. That slope is just another way of changing the input impedance of an antenna. Works the same way, and for the same reason that 'drooping' the legs of a 1/2 wave dipole antenna does. A very common way of doing impedance matching for a lot of years.
- 'Doc
- 'Doc
Just when I thought I knew 1/4 wave GP's, I get thrown a curve ball (so to speak)...I could NEVER get a true 1:1 match. Best I could get was around 1.5:1 - not too bad, just not 1:1.
With making a GP, Has anybody ever achieved a 1:1 match with a 1/4 wave GP (without using the tuning stub shunt method)?
Bob, KD5MHQ
With making a GP, Has anybody ever achieved a 1:1 match with a 1/4 wave GP (without using the tuning stub shunt method)?
Bob, KD5MHQ
If I remember correctly, putting the radials at a 45 degree angle should tune the impedance close to 50 ohms . . .
It's quite possible, but remember that it will be "perfect" at only ONE frequency. If it's "flat" from one end of the band to the other - especially at HF -- either the antenna or the feedline has a lot of losses. There is NOTHING wrong with 1.5:1 or even higher - as long as the transmitter doesn't cut back its power. If it's as low as you can get it, USE it.
Booty I have one of those "deluxe colinear" Rat Shack antennas in my basement. still works but it hasn't been used it in years. Was a family members and upon removal he was going to throw it out so I took it.
Marconi,
Is the hub in the pic from an A99 or is it one of your homemade ones?
Also, will a GP with a single sloping radial perform as well (in the direction the radial is pointed) as one with 4 radials?
Thanks!
I think the picture of the hub is an original GPK hub with four radials slanted down and three radials horizontal. I just drilled and tapped for three added horizontal radials.
I don't recall working my Marconi on air with only one sloping radial, but I did test the idea near 18' feet. My Eznec model of the idea also shows one radial will work very well, and depending on your mounting being well into the clear and at least 18' feet high, the antenna should work just fine.
As I removed radials from my antenna during my testing, I did find the antenna, with only one slanted element (radial), the match tended to be more like a full 1/2 wave dipole R=70 ohms J= <>0 ohms. So the match suffered a bit, but it was nothing to worrying about, the SWR was still below 1.50:1 at the radio.
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