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eHam Forums => Elmers => Topic started by: KC7KLZ on December 16, 2012, 08:34:02 AM



Title: Small footprint HF antenna....
Post by: KC7KLZ on December 16, 2012, 08:34:02 AM
Hi All,

I'm looking for ideas on how to make a small footprint HF antenna.  I live in a small apartment, and my only place to put up any sort of antenna is the balcony.  I live in a first floor apartment with a parking garage underneath.  So I'm about 16 feet up.  The balcony is 14 feet long.  I figure I have about 13 feet of usable length for an antenna.  My thoughts are probably a dipole with traps on it.  I've also been looking at the MFJ antenna tuner w/ the artificial ground.  Being up over 8 feet from the bottom of my balcony I think grounding might be an issue.

Any thoughts would be really appreciative. ??? ??? ???

'73

Eric Scott
KC7KLZ / VE7KLZ


Title: RE: Small footprint HF antenna....
Post by: WS4E on December 16, 2012, 09:38:51 AM
I am going to throw something else out.

This antenna has been getting popular in the portable ops crowd, especially for use with the new Elecraft KX3.  Its becoming almost as popular as the Buddiepole.

I got to see one recently that a fellow ham in our club purchased and I was really impressed with how well it works.

Its called the "Alex Loop".  It seems to work amazing for the size it takes up, and does not require any radials or anything like that.
http://www.alexloop.com/index.html

There are reviews of the alexloop here on eham too that you might want to read:
http://www.eham.net/reviews/detail/9012


If I lived in an apartment situation I would definitely look at it.  You might also look at the buddiepole depending on how much space you have to setup an antenna.




Title: RE: Small footprint HF antenna....
Post by: N3DT on December 16, 2012, 11:42:56 AM
When I was relegated to an apartment, I used some antennas I had on hand for mobile operations, called Ham Stick.  Only about 8' high, they are single band verticals, all you need is the counterpoise or even just a single ground wire at 1/4 wave for the band and you're in operation.  You can even wrap the counterpoise around in circles or whatever.  They may require some capacitance to bring to really good SWR which can be done with a BNC-T.  They're narrow band but usually cover most of the bands except below 30M.  I found them quite effective even off a fence post or mobile.  They're easily changed from one band to the other too if you get the quick disconnect arrangement.  Otherwise they just screw on and off.

http://www.abc-comm.com/HAMSTICKS_ANTENNAS.htm

I have no association with them and not sure they're still available.

Dave
N3DT


Title: RE: Small footprint HF antenna....
Post by: M6GOM on December 16, 2012, 05:22:12 PM
Look at the Cobwebb antenna. 20-17-15-12-10m full size dipoles in a 8ft square. The G3TXQ variant is the easiest to build.

http://www.karinya.net/g3txq/cobweb/


Title: RE: Small footprint HF antenna....
Post by: VE3PP on December 17, 2012, 05:35:03 AM
Look at the Cobwebb antenna. 20-17-15-12-10m full size dipoles in a 8ft square. The G3TXQ variant is the easiest to build.

http://www.karinya.net/g3txq/cobweb/

Good antenna but pretty tough to fit that on an apartment balcony.



Title: RE: Small footprint HF antenna....
Post by: KQ6Q on December 18, 2012, 02:55:07 AM
you don't have the space for a trap solution, but a tunable dipole, like the Buddipole, or its equivalent from Superantennas, would let you operate on several different bands, although you'd have to readjust to change bands. A hamstick dipole would also work, but would be a single-band solution, but would come in around $100 plus a mounting solution.


Title: RE: Small footprint HF antenna....
Post by: VE3PP on December 18, 2012, 04:31:39 AM
Years ago I made this antenna to use while I was camping.

http://www.hamuniverse.com/joystickantenna.html

With a 40 foot counterpoise I made contacts on 80 meters using that antenna. I was not licensed for 40 M and up at the time. But if I made contacts on 80 with it then it should make contacts on 40 and up.

You need a good tuner. I used a Dentron Jr. Monitor to tune with.



Title: RE: Small footprint HF antenna....
Post by: VA7CPC on December 18, 2012, 09:32:48 AM
I had two antennas when I was stuck with a balcony apartment:

1.  A metal "flagpole", 16.5' long, sticking out horizontally.  That was quite usable on 20m.   My landlord approved.  The balcony's metal railing served as a counterpoise. 

2.  A 31' JacKite pole, only used after dark.  You can build a loaded 40m dipole (loading coils in the middle of the elements, each element 15' long) and tape it to the pole.  Reasonably good results on 40m, and very nice results (with the coils shorted out) on 20m.  20-gauge copper wire was fine -- there's no mechanical load on the elements.  Coils were wound over 2-liter plastic Coke bottles, for light weight.

An LDG Z-11 Pro autotuner made life easy. 

The Alex Loop is good, but (I think) it's QRP-only.

Think about using CW and digital modes, rather than SSB.  You'll need every dB you can get.

.            Charles


Title: RE: Small footprint HF antenna....
Post by: KJ4FUU on December 18, 2012, 10:31:27 AM
You can also buy a dipole adapter for hamstick type antennas for about $20. You just clamp it to a mast,
and screw in a hamstick of your band of choice on each side. It's not the best performer, but an antenna
beats no antenna.

73,

-- Tom


Title: RE: Small footprint HF antenna....
Post by: N3DT on December 18, 2012, 04:23:28 PM
TenTec is selling the hamsticks for about $30.  You can get them on ebay for $20.  Just search hamstick.  I was always impressed with how good they worked for their size, but then that was in the last 2 sunspot cycles, the 15 meter one worked great mobile ssb for dx.  I'd always wanted to build a 40M beam out of them, it would be very narrow BW, but I bet for the size it would work great.


Title: RE: Small footprint HF antenna....
Post by: VE3PP on December 18, 2012, 05:02:42 PM
I used Hamsticks years ago when I operated HF mobile once in awhile. 40 Meters and up they worked pretty well. I had the 3 magnet mount on the truck roof. No extra ground from the magnet to the truck body. I also had one for 80 meters and made contacts at night on it up to 400-500 miles away.

I built a 17 M Hamstick dipole, stuck it on a rotor at 30 feet in the air and it actually worked fine. I have seen plans for the 20 meter Hamstick 3 element yagi.

Simple and easy to use if you can get a decent counterpoise wire in place. They are not going to be as good as a beam or a dipole 40 feet in the air. But they will get you on the air.

Another option would be the Screwdriver type of antenna. Not cheap but one antenna for all bands. Guys use those on stationary mobile homes. I know a guy who has one mounted on a mast in his back yard. Runs a 240 foot counterpoise wire around the fence line of his yard. He tells me it works great for what it is.


Title: RE: Small footprint HF antenna....
Post by: WA8FOZ on December 18, 2012, 06:51:41 PM
If you need to stay on the balcony, consider the MFJ magloop. Or maybe a folded dipole hung on the balcony above yours.

Off the balcony, the jackpole is a good idea. Two of them make a dipole. So do two 17-foot telescoping whips.


Title: RE: Small footprint HF antenna....
Post by: ZL3OF on December 18, 2012, 07:21:08 PM
How about a loop? If you have 13 feet available and 8 feet from floor to ceiling then 13+13+8+8=42feet, make it as big as you can. Feed it with twin line to a balanced ATU such as a single coil Z Match and it should work ok on 20 metres and above. It would be neat, tidy and unobtrusive with no need for a ground or counterpoise, apart from any station earth.
I don't suppose it would be much use on 80 but it might be better than nothing on 40/30.


Title: RE: Small footprint HF antenna....
Post by: KC7KLZ on December 18, 2012, 07:53:40 PM
Thank you very much.  There are a lot of good ideas.  I'm leaning towards the hamstick dipole, or the loop antenna.  Both have some interesting possibilities.  I'm looking at getting an MFJ 934.  It looks like it will do what I need it to do.

Again Thank You.

'73

Eric Scott
KC7KLZ / VE7KLZ


Title: RE: Small footprint HF antenna....
Post by: M5AEO on December 21, 2012, 11:36:53 AM
I am in almost exactly the same situation as you!  My balcony is about the same size.  I spent a great deal of time experimenting and my final antenna design is as follows.
Buy some plastic plumbing pipe about 13 feet long.  Wind 33 feet of insulated lightweight wire from top to bottom and attach to balcony railings (I use plastic cable ties, but use good quality ones).  Feed this into one side of a 1:1 balun and attach as many radial wires as possible to the other side of the balun.  The radials can hang down over the sides of the balcony, or lay them out on the decking (this will de-tune them but they do still work).  Best to add a common-mode choke then feed back to your shack using some coax (I use RG8) and into a decent ATU (I use a Palstar).  People will tell you that this is a great compromise, and so it is, BUT it does work.  I have worked Australia and Malaysia using 100 watts of SSB.  I generally run only 50 watts and still make good contacts all round Europe.  This week I worked Algeria on 20 and 15m.  You won't be able to go lower than 40m unless you start to experiment with loading coils.
Overall, this antenna has allowed my to get back on the air in a situation that I thought made radio impossible.  It's also very cheap to make: excluding the balun and coax it cost me about $10 to construct!

73 Jonathan, M5AEO, London UK.


Title: RE: Small footprint HF antenna....
Post by: KC7KLZ on December 21, 2012, 05:20:33 PM
This sounds great.  I'm still trying to picture it in my mind.  The wire is wrapped around the 13 foot pipe.  Then it is mounted horizontally on the balcony railing.  One end of the wire is attached to a 1:1 balun on one end, and the other end of the balun is a series of radials that are either hung over the balcony or laid on the deck.  This would effectively act as the other side of a dipole.  Then it is fed into the radio via a coax, and tuned with an ATU.  I might have to give this one a shot.  I can't lay the radials over the side of the balcony, but If I were to mount the pipe higher up on the upper roof, then run the radials down one of the side walls, would that be as effective?? 

'73

Eric

KC7KLZ / VE7KLZ   


Title: RE: Small footprint HF antenna....
Post by: M5AEO on December 22, 2012, 07:54:55 AM
No no!  Mount the pipe as a vertical, and the wire is wound on as a 'helical' element.  If you look in any of the antenna text books you should find various versions of 'helical vertical' antennas.  In my case I have been able to drop some of the longer radial wires over the side of the balcony: I have 14 radials and some of them are just sitting between the decking planks.. The balun will help to bring the feed-point impedance down to something manageable, and the choke should help with TV interference and common-mode currents on the outside of the coax feeder.  You will certainly need an ATU to get it to work.  I have had great success  even running just 50watts.
Good luck!

M5AEO