Building Hf Antenna

Started by Jim Boswell, June 21, 2012, 05:38:25 PM

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Jim Boswell

Hello,
Getting ready for Field Day. Today I have to finish building my 80/40meter dipole/inverted V. After that I will pack the radios and gear. This year we will be using two Tentec Hf rigs, an Icom IC-7200 and a 2/6mt SSB/CW/FM. Rig.
If I have time I will rig-up some solar panels to suppliment the batteries.
I hope you all enjoy  Field Day and be safe.

gil

#1
Hello Jim,

Could you share the dimensions of your dipole? Do you use traps? How high will the top of your "V" be?

80m requires such a long antenna, it almost doesn't seem practical to me...

I have  a PAR 40/20/10m end-fed dipole, and that is already 40' long. I plan on getting a telescopic fiberglass antenna mast, so I can lean it against the house pointing up. I also made a 20m off-center fed dipole with the SOTA tuner, and that is 50' long. But 80m!!! You need property to put that up! That's what, 140' of wire?

Have a great week-end,

Gil.

Paul

HF antennas, simple 1/2 wave dipoles, aren't difficult to make.  The 'magic' number is 468.  Divide it by the frequency in Mhz and the answer comes out in feet.  This is a 'ball-park' length usually slightly too long.  That's not a biggy, and it's certainly easier to shorten an antenna than to lengthen one.  It's also a fairly good idea to add a foot or so to the formula lengths to allow for making connections etc.  You will have to tune it anyway (adjust it's length) so a longer than necessary antenna will be shortened to the 'right' length in that tuning process.  Trimming from the ends of that dipole is probably the most common way to do that adjusting.  The biggy there is to keep the two 'legs' of that dipole equal in length (close works fine).  It's also a good idea not to cut the extra wire off, but fold it back onto the antenna.  It'll be there if you should ever have to lengthen the thing later.  No, that folding back onto it's self doesn't hurt anything.  What kind/size of wire to use?  Whatever you happen to have enough of that will support it's own weight and a little bit more.  Size isn't all that important at all.  Neither is if it's insulated or not, both work just dandy.  For example, a 500 foot spool of #14 insulated/stranded single conductor wire will make more antennas than you'll probably ever need.  A large spool of nylon cord/rope is also a very handy thingy to have.  It makes a very good insulator too.  It has to be strong enough to hold the antenna and feed line's weight in whatever your local weather is like.
Emergency antennas are only used for a fairly short time so don't have to be all that 'fancy' or 'high-tech'.  If it'll conduct electricity it can be used to make an antenna.  Use what you happen to have handy.  There are a lot of things that could be used, some handier than others, but still useful.
This is getting longer than I planned on so I'll quit here.
Have fun.
Paul

Jim Boswell

Hello Gil and Paul,

Paul is correct on the formula. For the 40/80 antenna I use some pieces of PVC pile to spread the wires apart. $ to 6in. works good and if you use the gray electrical PVC the antenna will last longer. In the Summertime, 80meters has a lot of static from TS. I use 80 mainly for Winter QSO'S. This past Field Day was a dud, the bands were not open. We made only 1 contact on 6mt, 0 on 10, 15 bands.
Good luck on the code, I never got good on CW, got my Novice and proud of that. I built a Heathkit HW-9 and am proud of that little rig. Even if I don't do CW most all my rigs have the CW filters and if need be I could could get a message out. I live near Socorro, and have some land for playing with antennas.
Take Care,  73'S  KA5SIW

gil

Hi Jim,

I have a kit on order from Small Wonder Labs, a Retro-75, AM transceiver on 3880kHz. I think I'll make an end-fed dipole for it. There are no tall trees around the house here, so it might be a challenge to install. I plan on getting a 33' telescopic mast, maybe an inverted V...

How would you describe 80-75m as far as conversations go? I know different bands have different "feels."

Gil.

Jim Boswell

Gil,
     We have lots of TS in New Mexico. For the most part, 80meters is out of action due to static most all Summer. Yes, the 80meter antennas can be a bit large. I use a Husler vertical antenna for 80meters. I like 15 meters for CW and SSB when the band is open. For the most part if you want to do CW on 40 meters you need a narrow IF filter. When I was just starting ham radio it was a bummer to spend all your money for a radio just to find out you need another 50-80 for an IF filter to hear 40meter CW.
     Sometimes you can buy the fiberglass poles that can be put together to form 20-30 foot uprights. There work good for 20 and 15 meter inverted vee antennas. The gray PVC pipe can also be used be telascoping one piece inside another piece, use cross bolts to hole them with about a 2ft. overlap. The white PVC gets brittle from UV in the sunlight. Some people are lucky and can use trees to hoist wire antennas into the air. 73'S  KA5SIW

gil

Hi Jim,

My K1 has three programmable filters, between 800 and 200Hz. It works pretty well. I wish it had a 2.6kHz filter to listen to SSB better. I can tune up to about 170kHz above the bottom of each band. No SSB transmit of course, only CW.

I could build a four-band filter board for it, which would get me 40, 30, 20, and 15 or 17m. Not sure if it would be worth it. I already have 40 and 20m.  probably couldn't sell the dual-band board, so I'd basically be out $100. Or I could unsolder some components off the 40/20 board and make it a 80/something. Though changing boards is a pain..

Have a great week-end,

Gil.

Lamewolf

Use the formula 468/freq in mhz = length in feet.  Using 3.5 mhz get you around 135', then feed that 1/3 off center (45' one side, 90' on the other) with a 4:1 balun and you have a Windom type antenna that will work several bands without a tuner !

Lamewolf

Quote from: gil on June 22, 2012, 10:01:54 PM
Hello Jim,

Could you share the dimensions of your dipole? Do you use traps? How high will the top of your "V" be?

80m requires such a long antenna, it almost doesn't seem practical to me...

I have  a PAR 40/20/10m end-fed dipole, and that is already 40' long. I plan on getting a telescopic fiberglass antenna mast, so I can lean it against the house pointing up. I also made a 20m off-center fed dipole with the SOTA tuner, and that is 50' long. But 80m!!! You need property to put that up! That's what, 140' of wire?

Have a great week-end,

Gil.

Gil,

If you don't want to use a full size dipole for 80 meters, you can get by on a 88' doublet fed with either 450 ohm ladderline or 300 ohm TV twinlead and use a tuner to match it.  Thats like a dipole that 44' on each side, but with a tuner it will work 10 thru 80 meters and works quite well !  I use one as a field day antenna with the center supported by a 31' telescopic Jackite pole www.jackite.com  My 88' doublet is made from #20 speaker wire and fed with cheap Radio Shack 300 ohm TV twinlead.  For 10 thru 40 meter coverage you can even go shorter with a 44' doublet.

KC8AON

gil

QuoteIf you don't want to use a full size dipole for 80 meters, you can get by on a 88' doublet fed with either 450 ohm ladderline or 300 ohm TV twinlead and use a tuner to match it. 

Yep, once I get the tuner for my KX3 I might have enough space for one... It won't be very high but good for NVIS.

Gil.

Lamewolf

Quote from: gil on November 15, 2013, 07:24:58 PM
QuoteIf you don't want to use a full size dipole for 80 meters, you can get by on a 88' doublet fed with either 450 ohm ladderline or 300 ohm TV twinlead and use a tuner to match it. 

Yep, once I get the tuner for my KX3 I might have enough space for one... It won't be very high but good for NVIS.

Gil.

The only clinker with this antenna is that a lot of the built in autotuners don't have enough matching range for such an antenna so its good to use a manual tuner like one of the cheap MFJ Tmatch tuners or a balanced tuner like the Emtech ZM2 Zmatch tuner.  I homebrewed a clone of the ZM2 and it matches the 88' doublet quite well 10 thru 80 meters !  Good luck !
KC8AON