Using a 102" as a base

[ajw2685]

Ok, I know, I know. Just buy an A99 and use an actual base antenna. BUT, this will be setup at my parents house since I will be in an apartment for the next three years while I attend Grad School. Also, I really don't have a place to mount an A99 that my Father would approve of. He sure is not going to let me mount one on his roof, he just had a new roof put on this summer. I thought about mounting it on our garage/shop but again, he just had a new roof put on that this summer too. The primary goal here is short distance communication between friends and family. My brothers truck has a Wilson 2000 and my car has a Wilson 1000. If we want to talk skip, we just go mobile. So, what all do I need to do to use a 102" as a base antenna. I have read about people hiding these in trees where they have covenants against antennas in yuppie neighborhoods. My biggest concern is getting it grounded out and what coax I should use. Any suggestions/ideas would be appreciated.

 

[Beetle]

You're going to need a good ground plane (not the same thing as "getting it grounded out"). This can be radials or a large sheet of metal. You have to substitute something for the metal frame/chassis/body of the vehicle that the 102 would normally be installed on.

 

[SR385]

Three pieces of 12ga wire 102" give or take, long soldered to where your shield of the coax can connect to it. Pull them out equidistant as a triangle and about 45 degree angle to the vertical element.

Trim the lengths of the ground plane wires to get the SWR adjusted.

 

[ajw2685]

Three pieces of 12ga wire 102" give or take, long soldered to where your shield of the coax can connect to it. Pull them out equidistant as a triangle and about 45 degree angle to the vertical element.

Trim the lengths of the ground plane wires to get the SWR adjusted.

Thanks for the information. Would something like No. 9 wire work? It is thick/stiff and won't bend in the wind.

 

[SR385]

Thanks for the information. Would something like No. 9 wire work? It is thick/stiff and won't bend in the went.

Yup. The difference will be that as the thickness of the wire changes, it's velocity factor also changes so the length will vary from thin to thick wire a bit.

Cut long, trim later.

It should work pretty well. Sometimes with antennas it's hard to admit that something simple will work as well as something that looks much more convoluted. It gets a lot worse with higher frequencies too. UHF 1/4 wave are just tiny suckers but they still get the job done...it just doesn't 'look like' it should work.

 

[Marconi]

Well SR385 is right on the money as far as I'm concerned.

Homemade 1/4 wave SS whip for base

Uses an L-bracket mirror motor mount and a hub from an A99 for the ground plane

 

[hotrod]

well im glad i came across this.as i got a friend wanting to
get a setup going.he lives in town with very close neighbors
so he didnt wanna fork out 50-100 bucks for a antenna
he cant use due to tvi.the only thing i question is were is
the 6 inch spring?seems everyone says the 102 whip needs
the spring to tune for 11 meters.i already got the whip
and hub and gpk only problem is 1 radial the threads are
about shot would 2 work ok

 

[Beetle]

The more radials the better. You might need to add a few inches to the radiator to compensate for the lack of the spring. Then again, you might not. That's where experimenting comes in.

 

[FL Native]

you could allways skip the whip and just use wire. make a simple di-pole. 108 inches up to the center of the coax and start with about 118 inches for the down side and hook it to the shield of the coax. trim the longer end after you get it set up to ajust the swr. you could get fancy and hook up a 1:1 balun at the antenna feed point. 8)

 

[Marconi]

2685, do as 385 suggests and work with the GP radial element for your tune.

You need to keep the radiator showing a bit of capacitance and adding a 6" spacer or a spring is probably not going to be of much benefit in this setup. If you get it close to tune you should be able to make it resonant right in the middle of 11 meters with a typical 102" whip. I get much better tuning response working with the GP radial length and their being a little longer is better up to a point.

The more radials the better, but if you can use at least three 1/4 wave electrical length elements in the GP you should get it to work fine.

You can also affect the match some by adjusting the angle. I have found 45 is a very good compromise angle. Personally I prefer to work my 1/4 wave with a bit of mismatch and have the GP more in the horizontal, I get more gain on my field strength meter. However if you want a really good match, start out at 45 degree down from vertical. You may see less gain, but your match will be better and your bandwidth should also improve.

If you feel the need to try and tune this one to a more perfect SWR, then try moving the angle of the GP up or down if you are able to do that. I find lowering the angle down tends to raise the 50 ohm resistive match closer to 50 ohms at the feed point and raising it up towards the horzontal does the opposite.

Good luck, you will find this antenna is pretty remarkable the way it will perform if you can get it up about 40+ feet.

 

[ajw2685]

40 feet is stretching it. I could get 20ish no problem, maybe 30, big maybe. I had someone lined up with a free TV tower, 20-25ish feet worth. I need to hunt them down again.

 

[hotrod]

well one i had in mind will only be about 20ft. my friend not
allowed a big base antenna however landlord said could use
a mobile if he wanted tono higher than 20ft.were about
15-20 miles apart and talk ssb i figure this setup shouild
work for that.hopefully the swr will be below a 1.5 thats
all im really concerned about.dont wanna fry his radio gear

 

[BIONIC_TEXAN88]

i used a 102" whip and 3 8' ground radials I rigged up at 30' to the base. worked very well and I had no problems hitting folks 30-50 miles away on ssb. swr was low as well (1.3-1.5).

 

[Switch Kit]

I remember that one Tex , real close to Marconi's links . DAMN !! I love it when a plan works out !!

 

[ajw2685]

I figured out how I am going to mount this thing on my parents house. This also means I could be using an actual base antenna. Ok... Follow this carefully!

I am going to build a mount out of 2x4s and plywood (either treated or painted/sealed) in the shape of a wide "V". It will ultimately look like a "W" but without the outer top halfs of the sides. This will sit on the peak of my parent's house and I can place two cinder blocks on either side in the smaller "V's" to hold it in place. I can then build supports off of this to bolt a pipe to that will hold the A99.

I am so happy I finally figured out a way to mount my antenna that isn't permanent and won't put holes in any of my Father's roofs!

Time to order the A99 and 100+ feet of coax.

EDIT: My Picasso style drawing should better explain my plan.