Long Wire Antenna for HF

[zz0468]

The op said he was looking for "field expedient that I could throw in my cargo pocket and move out". Stuffing even that micro tuner from MFJ in the pocket of the BDU and letting it beat me in the leg is not my idea of a fun day."

That's hardly a realistic scenario when you're talking about HF. A VHF or UHF HT, maybe but HF? LOL...

I get it. The OP wants small and light. That's doable. Pocketsize, with any chance of working someone, not so much.

He mentioned 20 meters. A single band dipole fed with RG174 might be ok. A 5 watt transmitter feeding a dipole with 35 feet of RG174 would have an ERP of a bit under 4 watts. I used to do backpack camping and took an HW7 with me and used a dipole fed with RG58. It was plenty small and light enough. Worked all over the world with that.

Anything you can come up with that meets his requirements is going to be a compromise.

This is true. But performance doesn't have to be one of the things compromised. There are plenty of successful QRP operators out there, and the secret to their success is paying attention to antenna efficiency and losses. It's relatively easy to get a 4 watt ERP with a 100 watt transmitter. It takes a but if thinking to get a 4 watt ERP with a 5 watt transmitter.

Yes the RG-174 is a compromise. It serves two purposes. It attenuates the reflected power as mentioned.[/quote]

As well as the forward power. Why!? Why would you want to do this when there are better solutions?

It also keeps the size and weight down to meet the stated requirements. He is asking for something for quick deployment and easy transport and the best you guys can come up with is a full size rhombic.

Absurd. No one suggested a rhombic.

So, do any of you geniuses have a suggestion for the op that meets his requirements or not?

You betcha I do!

Single band dipole, RG174 feed ok for short runs. Multiband dipole, use 300 ohm ribbon line and a mini-tuner.

And some advise: RG174 is pretty fragile stuff. You're not likely to be wanting to string your antenna real high for practical reasons, so you might consider using RG58 for better durability. The losses of RG174 are manageable at HF if the VSWR is low, like you get with a single band dipole. Running it as a non-resonant multiband dipole can see VSWR run to 20:1 or more.

At 28 MHz, that can make the feedline loss for a 35 foot piece run from 1.5 db (1:1) to over 6.5 db (20:1), so I strongly recommend you don't use it in a multiband antenna.

 

[prcguy]

I'll again suggest a ZS6BKW which for portable use can be a 94ft dipole fed with about 40ft of small lightweight TV twinlead. It's resonant and useable without a tuner on 40, 20, 17, 12, 10 and 6m.

Just Google the antenna to get the basic dimensions and initially cut the feed line in small increments until it matches on 40m and your good.

The performance is great and similar to a G5RV used with no coax and a tuner at the end of its balanced feed line but you don't need a tuner unless you operate 80 or 15m.

For portable use I get plastic chalk line reels from Home Depot and replace the string with 47ft of thin wire and about 30ft of guy string. I also install BNC connectors on the TV twinlead feedlline, which is not easy but installing PL-259s is. In either case make good strain reliefs at the connectors with hot glue style heat shrink. The feedlline to wire connection can be a Pomona female BNC to binding post adapter or a mil surplus dipole center insulator.
prcguy



Quote:
Originally Posted by jhooten
So, do any of you geniuses have a suggestion for the op that meets his requirements or not?

 

[gigyahurts]

Greetings,

I'm looking for advice on a long wire antenna for HF operations. I'm look at the 20 meter band as my place to start. I have a PL-259 connector and a spool of speaker wire from Radio Shack. The idea I had was to run the wire directly into the connector and then use a rope to put the antenna up in a tree. The radio I'm using is the FT-817. I'm leary about high SWR so I want to get this right before I make a mistake.

I use a 857 at 25 watts for my field radio and a roll up dipole that I can roll out to 80 m or 40 m which gives me NVIS coms 24/7 all year in my area. Making one for 20 only would be even smaller. I made the antenna from electric fence poly line which is 2mm polypropylene rope with ss strands in for carrying the current. I also cut some small plastic spreaders that clip on to the line to make a ladder line. I don't use any insulators on the end as the 1.5mm dacron cord insulates enough. There is a short 4" stub of coax to join up the line and I put heat shrink on the first few feet of wire to eliminate wind twisting and causing a short.

I spent a bit of time with an analyser to set all the dimensions properly and tied knots in the line for the top ladder connector and on each side for the 40m dim. For 80 you roll it all out. It is set for a max height of 3.5m and will work down to 2m in the middle. The excess line shorts out on the small aluminium spool when on 40 to terminate the line.

I borrowed heavily from Bonnie's design KQ6XA Antennas by Bonnie Crystal but made mine for my specific task. My antenna weighs about a pound, will fit in my pocket and is near indestructible. It works well on both frequencies it is set for with a near 1:1 swr. It is pretty narrow in bandwidth but can be adjusted for higher or lower in the band by an extra wrap more or less on the spool. Set up and recovery takes about 2 to 5 minutes each and only uses two tie points that are as high as you can reach and benefits from set up in gullies and can be set up in darkness by feel.

If you want a single band antenna only, your insulated wire will work fine. Measure it out to the calculated middle of the band or where you want to work and put a minimum xmit on it to check swr if you cant borrow an analyser. Adjust as required.

 

[LtDoc]

The only real problem with most of the suggestions deals with the feed line. Sorry, but that RG-174 is really worthless at HF and the typical feed line lengths. The problem with it is that it attenuates thing in BOTH directions. You may still have some power at the antenna when transmitting, but how about the attenuation of the received signal, how much of that can you afford to loose? That makes no mention of how to put connectors on the stuff for the typical radio? It's really not worth the trouble. Just how 'portable' does it have to be?
- 'Doc

 

[prcguy]

My portable ZS6BKW with chalk line reel elements is very light weight and fits in a small side pocket on the pack for my 20w HF mil backpack radio. TV twinlead seems lighter in weight than RG-58 coax.
prcguy

The only real problem with most of the suggestions deals with the feed line. Sorry, but that RG-174 is really worthless at HF and the typical feed line lengths. The problem with it is that it attenuates thing in BOTH directions. You may still have some power at the antenna when transmitting, but how about the attenuation of the received signal, how much of that can you afford to loose? That makes no mention of how to put connectors on the stuff for the typical radio? It's really not worth the trouble. Just how 'portable' does it have to be?
- 'Doc

 

[41a0203c]

Thanks for all of the feedback everyone. After reading all of the replies, I have some good ideas now.

 

[41a0203c]

I will definately check out the antenna you recommended. The reason I want to stay light weight and portable is because of some of the fun I had in PRC-150 training a few years ago.

 

[prcguy]

Did the PRC-150 happen to follow you home?
prcguy

I will definately check out the antenna you recommended. The reason I want to stay light weight and portable is because of some of the fun I had in PRC-150 training a few years ago.

 

[41a0203c]

Nope. I had to leave it with the unit when I got out. I bet its sitting on a shelf collecting dust.

 

[DcotorWu]

This guy here has it right. I have done this in various lengths of wire a dozen times. Works fine. You can use just about any wire and even pieces of pvc pipe for insulators. The main thing is to try it. You will see. This dude has it right.
$4 Special Antenna by W1GFH - The Four Dollar Special Antenna!

73 Doc