Base Cb Station

[peacefrog922]

I recently purchased a 102" whip on a spring mount and I am using this as a base station set up. I have it mounted on a fence post with a 5ft extension. I am also using a 100' RG8u cable to my Uniden 980SSB. I cannot get my SWR under 3! Any suggestions to lower the SWR?

 

[prcguy]

The whip needs a lot of sheet metal under it or at least some 9ft ground radials to work. You basically only have half the antenna if you didn't supply a ground plane. 100ft of RG8 is not great either, the loss will be starting to add up and that much coax is actually hiding what the real SWR is making it look better than it is.

Why not get an actual base antenna, which will be large, and move it so you don't need so much coax?

 

[AM909]

RG-8 is a bit less than -1 dB for 100 feet at 27 MHz. Even if you could cut that in half, I doubt you'd be able to hear the difference.

Add four, 9- to 10-foot long, 45-degree down-drooping, wire ground radials, spaced 90 degrees around the center.

Seems like the whip is a little short. A quarter-wave at 27 MHz is 104-109", depending on velocity factor.

 

[prcguy]

SS whips are typically 102" and with the 6" spring mount that's 108". I've never seen a whip longer than 102" except for a special 110" or so fiberglass version for a Shakespeare HF marine antenna. I have one of those longer whips in the garage somewhere. No need to droop the wire radials down, three or four 9ft wires straight out will match up just fine.

RG-8 is a bit less than -1 dB for 100 feet at 27 MHz. Even if you could cut that in half, I doubt you'd be able to hear the difference.

Add four, 9- to 10-foot long, 45-degree down-drooping, wire ground radials, spaced 90 degrees around the center.

Seems like the whip is a little short. A quarter-wave at 27 MHz is 104-109", depending on velocity factor.

 

[AM909]

SS whips are typically 102" and with the 6" spring mount that's 108".

That's what I was missing – the spring.

No need to droop the wire radials down, three or four 9ft wires straight out will match up just fine.

There's another thread somewhere here that addresses the reason for the downward angle (raising? the impedance, AFAIR), and goes into detail about the affect of the length, number, and spacing of radials.

Of course, everything's relative. To adapt a famous legal quotation, with a good tuner and/or right feedline, you can tune up a ham sandwich.

 

[prcguy]

There are lots of other threads addressing the reason you don't need to bend the radials downward also and no tuner would be needed in that case. I probably authored several of those other threads and I won't go into the details here unless someone asks.

That's what I was missing – the spring.


There's another thread somewhere here that addresses the reason for the downward angle (raising? the impedance, AFAIR), and goes into detail about the affect of the length, number, and spacing of radials.

Of course, everything's relative. To adapt a famous legal quotation, with a good tuner and/or right feedline, you can tune up a ham sandwich.

 

[peacefrog922]

I just added speaker wire ground radials. The antenna is approx 8-9 feet off the ground and there is a ground base that has 6" metal rods coming off of it and I threaded the ends of these and added the ground radials. 6 of them 60 degrees apart. I am running rg8u cable 100ft. I still can't get the SWR under 2.6. I am not sure what else I can do??

 

[peacefrog922]

The "radials" are tethered to the ground, so they are approx 14 ft long and tied down at approx 45 degree angle.

 

[AM909]

Using a frequency of 27 MHz and a velocity factor of 0.95, a quarter wave is about 104". A couple of sites have recommended the radials be 10-12% longer, which would be 114–116" or about 9 1/2 feet. I don't recall how sensitive the radial length is, and don't know what the correct VF for speaker wire is , but you might try trimming them down to about 10 or 11 feet to see if it improves the SWR, then trim small amounts from there to find a dip, trying to keep everything else constant, like body and cable positions.

 

[prcguy]

Shorten the ground radials to about 9ft.

I just added speaker wire ground radials. The antenna is approx 8-9 feet off the ground and there is a ground base that has 6" metal rods coming off of it and I threaded the ends of these and added the ground radials. 6 of them 60 degrees apart. I am running rg8u cable 100ft. I still can't get the SWR under 2.6. I am not sure what else I can do??

 

[iMONITOR]

I don't understand why so many people put antennas designed for use on metallic mobile vehicles on their house. Why not use antennas designed for a base? Sure you can make it work but I think you'd be sacrificing performance regard of what you convert, modify, or add. Same for scanners, why? I understand if that's all you can afford or it's something you have laying around in the garage, but why intentionally buy an antenna that's not designed for what you intend to use it for?

With all those cookie sheets and pie/cake pans on he roof it must look like Martha Stewart or Betty Crocker lives there!

 

[Mophead]

I had a similar setup years ago. The whip was old and completely rusted to it's spring. I used a piece of plywood as a base and made four 9 ft radials with thick aluminum grounding wire and had it all laid out on my flat rowhome roof. Almost had a perfect flat match and got out really well.

 

[merlin]

What do you have for radials, That is important.
If you have ever seen a droopy drawer antenna, they are your whip (or =) with radials pointed downward at 43 degrees. This provides your 50 ohm impedance and best horizontal gain.
If your whip is 102 inches, it is intended to be used with a spring and that will further reduce your SWR.
Cheers

 

[merlin]

There are lots of other threads addressing the reason you don't need to bend the radials downward also and no tuner would be needed in that case. I probably authored several of those other threads and I won't go into the details here unless someone asks.

Horizontal radials will significantly raise the departure angle of the antenna with 1/4 wave ground plane.
(sometimes a good thing like skip)
By bending them down, that gives a better horizontal departure.
They can even be straight down (like a bazooka antenna) with a slight loss in gain.

 

[merlin]

The "radials" are tethered to the ground, so they are approx 14 ft long and tied down at approx 45 degree angle.

From the whip, shorten them to about 119 inches. you can use insulators to tie them off.

 

[N8YX]

I don't understand why so many people put antennas designed for use on metallic mobile vehicles on their house. Why not use antennas designed for a base? Sure you can make it work but I think you'd be sacrificing performance regard of what you convert, modify, or add. Same for scanners, why? I understand if that's all you can afford or it's something you have laying around in the garage, but why intentionally buy an antenna that's not designed for what you intend to use it for?

With all those cookie sheets and pie/cake pans on he roof it must look like Martha Stewart or Betty Crocker lives there!

I've installed many 1/4w whips w/ tuned radials in place of so-called "base antennas" and they've all worked well IF they're mounted at least one wavelength up. In the ham world, a 6BTV is a quarter wave on every band which is covered. Mine is mounted with the base at 30ft, and uses four tuned radials per band.

No complaints with either setup. An omni is not the equivalent of a Yagi at 100ft but I haven't had trouble working anything I want.