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Explain the counterpoise/ground...

T

The Jerk

Active Member
May 6, 2008
647
66
38
Reading, PA
I am trying to set up a stealth base antenna. I attached a 102 whip to a metal pole...figured the metal pole would act like the counterpoise.
Got everything hooked up, Grant XL, rg8, and ended up with a 1.7:1 on 20. All indications point that the antenna is too long, and I've already cut 3 inches off it. Its not getting any better by cutting it off...its already short without the spring.

Should I worry about it?

Sent from my SAMSUNG-SM-G730A using Tapatalk
 

My swr was way lower when I had my 102" on top of my deep fringe stacked tv antennas. I was using my tv antenna booms for makeshift ground plane radials.
For 27.205 MHz a 102" whip should be fine if you didn't cut any off of it.
You might not have everything grounded right. I have my radio equipment and antenna tower grounded to earth.
Check this out.
CB Radio DIY Antenna - YouTube
The 102" Whip CB Base Station Antenna - YouTube
 
The Jerk said:
I am trying to set up a stealth base antenna. I attached a 102 whip to a metal pole...figured the metal pole would act like the counterpoise.
Got everything hooked up, Grant XL, rg8, and ended up with a 1.7:1 on 20. All indications point that the antenna is too long, and I've already cut 3 inches off it. Its not getting any better by cutting it off...its already short without the spring.

Should I worry about it?

Sent from my SAMSUNG-SM-G730A using Tapatalk
Click to expand...

I would not cut the antenna.Have a problem of impedance, because the installation is incorrect.
The impedance has nothing to do with the antenna resonance.To find out where an antenna resonates, you need a "grid-dip meter", not a SWR meter or a "antenna analyzer".
We always try to get 50ohms at the point of feeding an antenna, but a dipole is resonant 70ohmios approximately 1/2 wavelength on perfect ground.
This never happens in the real world.
You should try to get a better installation of the antenna, which will ensure better performance and more approximate impedance coupling.

no see
 
nosepc said:
I would not cut the antenna.Have a problem of impedance, because the installation is incorrect.
The impedance has nothing to do with the antenna resonance.To find out where an antenna resonates, you need a "grid-dip meter", not a SWR meter or a "antenna analyzer".
We always try to get 50ohms at the point of feeding an antenna, but a dipole is resonant 70ohmios approximately 1/2 wavelength on perfect ground.
This never happens in the real world.
You should try to get a better installation of the antenna, which will ensure better performance and more approximate impedance coupling.

no see
Click to expand...

No see:
:oops:
Why did you choose not to tell him that the 1/4 wave vertical antenna needs some ground planes mounted at a 45 degree angle/downslope to match the impedance to 50 ohms?


The Jerk:
You may need to add some length to it now that you've trimmed off some length. You can do this by adding some length at the antenna base with a spring or spacer. Three inches is a lot to remove from a 1/4 wave whip, it will have consequences. What freq did you intend to use it on, CB or 10m?
 
Last edited:
SWR on 1 was about 1.6:1 and just about 2:1 on 40. That means it needs to be shortened, according to the equipment I have available. I was just trying to set up a quick base with a spare Grant XL. I built a horizontal dipole using 102s at the last place and it worked phenomenally for skip, but it sucked for talking local. That's the reason I was trying to make a vertical. I thought the steel pole would act as the counterpoise? I can redo it, and use a second 102 for the counterpoise; but... That's why I asked the question... Further: Cutting the whip did NOT affect the SWR as you would have expected...there was no change before to after.
 
The Jerk said:
SWR on 1 was about 1.6:1 and just about 2:1 on 40. That means it needs to be shortened, according to the equipment I have available. I was just trying to set up a quick base with a spare Grant XL. I built a horizontal dipole using 102s at the last place and it worked phenomenally for skip, but it sucked for talking local. That's the reason I was trying to make a vertical. I thought the steel pole would act as the counterpoise? I can redo it, and use a second 102 for the counterpoise; but... That's why I asked the question...
Click to expand...

You can take your horizontal dipole that you already made and suspend it vertically and it will work, so long as the coax feeder is perpendicular to the dipole for four or more feet.

But when using a 1/4 wave vertical, it will need to have the appropriate ground planes as suggested above. If your mast support was the same length as the whip, it probably would work so long as you used fiberglass masts to support it underneath. It should have a SWR of 1.5 @ 75 ohms impedance which is typical for a dipole - BTW. 17.2 ft long overall. However, the coax's position will affect it - IIRC.
 
Yeah, that whole "feed being out four feet" is almost impossible for me. Looks like I'm going to have to look at another option. I don't exactly have the room to make it a horizontal now.
 
To get some antenna length back you might could spiral some solid conductor copper wire onto the whip's top to extend it if you don't want to buy another one.
 
The Jerk said:
Yeah, that whole "feed being out four feet" is almost impossible for me. Looks like I'm going to have to look at another option. I don't exactly have the room to make it a horizontal now.
Click to expand...

If you've tied the coax to the metal mast you'll have common mode on the coax and this may affect the SWR reading. Create a RF choke, place it at the antenna socket or as near as possible and bring the coax down keeping it away from the mast.

It'll reduce or hopefully eliminate common mode current, may lower noise and it'll probably have an effect on the SWR.
 

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