ICOM AH-710 type of folded dipole

[KF9CM]

I was wondering about the ICOM AH-710 folded dipole antenna. First of all I think they want too much for it ($300). I guess the cost comes from the non inductive resistor (470 ohms @ 150 watts). This appears to be an 1.8 to 30 MHz antenna.  I would assume it wouldn't be to hard to make except for the resistor. any thoughts?   

 73 de Gary,KF9CM

[Mike/W8BAC]

I used the G5RV version when I rented a small place and had limited space. It was a huge disappointment. The resistor on that (Icom) one is a bit wimpy. how much power are you going to pump in to it?

Any sort of dipole, zep or even a random wire with tuner would be better in my opinion. The G5RV type antenna is a cloud burner and you'll regret spending the money.

What is your situation, yard size? Can you find the room for a dipole?

Mike

[ka3zlr]

Welp, if we're gona put up That folded Dipole, put up the Barker Williamson version...Do Not Run any real power...No serious carrier Old buzzards...makes great smoke... had one given to me...It lasted one season...Eh...

Now if you have a coupla trees, and can create a "square in the air" or close facsimile there of...Put up a Loop OM...vertical or horizontal...great limited space antenna...feed it with coax, balanced line tried em both it works...a loop on 40 vertical.. man i made some smoke with that thing...on 7.290 AM...when i ran the viker II...Loops are fun to experiment with...if yer short on room..now myself on 75/80 i prefer a phased array.. but dat needs room...

Also try a Coaxial Double bazooka.. neat antenna, all made from same coax...it's a band specific antenna..but they're great for throwing over a tree...Real quick ..... get on the air fast and will tolerate some power...Nice Noise canceling effect too...they're also a Terminated antenna...

Have fun 73.

[AF9J]

Hi Gary,

The problem with the G5RV is that stupid length of coax put into it, within the last 25 years or so, to make 80s & 90s solid state transceivers with wimpy internal tuners, able to match up to it.   This coax section gets downright lossy at certain freqs.  On 17m for instance the modern G5RV is like an aircooled dummy load.  The original balaced line only version of the G5RV is an OK antenna.  

As for the folded dipole AH-710 - as soon as I read about the resistor in it, I figured there were going to be losses.  The resistor is to help out impedance at certain freqs by adding a resistive load, and as such disspates RF as resistive heat losses, when you want radiation. The B&W folded dipole is similar to the AH-710. It'll match 2:1 or less just about anywhere, but at many freqs, is like an air cooled dummy load for radiating RF.

I agree with Mike.  Use a zepp or a random wire.  If you have to, don't run it in a straight line so you can get extra length out of it.  There will be a loss of efficiency compared to a straight line antenna, but it won't be huge.  If you can (I can't), use balanced feeders, or at least a counterpoise.

73 & with just my 2 cents,
Ellen - AF9J

[Steve - WB3HUZ]

Could you tell us why you would want to use this antenna? What are your requirements, limitations, preferences and the like?

Just to be clear, the G5RV is a dipole - just one of a special length. It was originally designed as a 3/2 wavelength antenna for 20 meters. This length produced the radiation pattern G5RV wanted at that time. Later, it was discovered that when fed with particular lengths of open wire, easy matches were obtained on several other bands.

At some point, a balun was added at the end of the open wire line and coax introduced to the system. It seems this made the antenna more popular or easy to use with most hams since they were familiar with coax and it easily interfaced with their radios. Depending on the quality of the balun and the length of coax used, the G5RV could suffer significant losses on 75 meters (160 meters, forget it). Many hams still used a tuner with the G5RV. That never made much sense to me. If you are going to use a tuner anyway, just run the open-wire or ladder line right to the tuner.

There is nothing intrinsic about a G5RV that makes it a cloud burner. The take-off angle (high, as in cloud burner or low as in DX antenna) is purely a function of its height about ground relative to wavelength.

Anyway, the resistive loaded folded dipoles are very wideband and usually will not require a tuner. But since resistive loading is involved, some loss is introduced. Just how much depends on the frequency (at can be several S units worth on the lower HF frequencies for the typical 90 foot length of these antennas). So, you must ask yourself how much loss you are willing to suffer for frequency coverage/agility and/or not needing a tuner.

Here's some good info that may help you answer these questions.

http://www.cebik.com/content/a10/wire/wbfd.html

A free registration is required (lots of other good antenna info at this site).


Info and measurements on the G5RV at the links below.

http://www.vk1od.net/G5RV/index.htm
http://www.vk1od.net/G5RV/optimising.htm

[KF9CM]

Thanks for the replies,
I've used a G5RV on several occasions as a field day antenna and it worked well on 40 meters but not very well on 80. The reason I asked about that folded dipole was, I was intrigued by the design and from what I gather, it's not worth putting up. I guess that 470 ohm resistor makes a good dummy load .
I've got a 120' dipole fed with 450 ohm twin lead. My problem is I've got the room, but I've got a lot of trees that interfere with the radiators and feed line. I tried a full wave loop but with less then desirable results.  Maybe I should setup the dipole and fire the 4X1 amp for about an hour to burn out the obstructions .


de Gary, KF9CM

[w3jn]

I've got a 120' dipole fed with 450 ohm twin lead.

All you need is a Junkston Matchbox or HB balanced tooner and you have it made.  No reason to buy that Icom antenner.

BTW that antenna is known in some quarters as the T2FD and meant to be "tilted".  It is at best -3dB from a resonant dipole, and that resistor is most certianly meant for SSB or CW duty cycles, NOT AM.  It's probably better for SWLing in receive mode only.

[N3DRB The Derb]

hire someone to cut down the bad trees and leave only the good antenna trees.

[The Slab Bacon]

Build one, leave the resistor out (leave it open at the top), feed it with ladda line and a good tuna and your good to go. I have been using one like that for a lllloooonnnngggg time with very good results. Scroll back through this section and look for my thread called "a short antenna that works" I posted a drawing and all. Several others have built it with good results as well.

                                              The Slab Bacon

[N3DRB The Derb]

Slab I bet that would work gud at my place fer 160. I should get the W7FG 75 ant outdoors and re-do the brown crap fed antenna for 160 using your design. Switch em with that big assed knife switch MOP gave me. Ebay is full of cheap bows and arrows for antenna stringing. Wish I could find the other side of the antenna, I sure could use that rope again. I'm gonna go out again and look for it some more.

[KF9CM]

We've got an ordinance from the tree huggers in our village not to cut down trees, Derb, but luckily I can trim. I looked for the  "a short antenna that works" thread, Slab,  and it didn't come up, but I've got the picture. One of the best antennas I've got is the 18HT "High Tower". I've got a 5" loading coil for 180 meters that works well. It's great on 80 for DX, but the problem is receive. During a skip cycle I had a QSO with a guy in Australia, on 80 meters, he could hear me but I had to get a relay from someone for the reception. Right now the 18HT is down due to too many branches. I'm trying to get the tree guy out for that.

I have two lots and the longest point is diagonal across both lots ( 140 feet), In the back of the lots there is a 7000 volt line running on top of the power poles. I dare not get close to that (I wish they'd bury the darn thing). By hook or crook I'll get something up.

TNX de Gary,KF9CM

[WA1GFZ]

get around the rules. Dig a hole next to the trunk and bury a bag of 10-10-10 in the hole and feed it to death. Nobody will bust you for taking down a dead tree.

[The Slab Bacon]

Gary,
        Check Here:       http://amfone.net/Amforum/index.php?topic=12710.msg93883#msg93883


                                                   The Slab Bacon

[W1AEX]

Thanks for the replies,

...I've got a 120' dipole fed with 450 ohm twin lead. My problem is I've got the room, but I've got a lot of trees that interfere with the radiators and feed line...

de Gary, KF9CM

Hi Gary,

I ran into the same tree interference problem at both ends of my antenna and also at the feedpoint. The solution for me was a "48 inch high limb rope saw" which allowed me to clear a nice swath for the wire and the feedline. Costs around 50 bucks with shipping, is a great cardio work out, and will cut limbs up to 8 inches in diameter at 75 feet (I've done it) if you add rope to each end.

Rob W1AEX

http://www.northerntool.com/webapp/wcs/stores/servlet/product_6970_12415_12415

[Steve - WB3HUZ]

You can run the antenna through the tree, if you can string it without snags. It will work fine. Just  use insulated wire.

We've got an ordinance from the tree huggers in our village not to cut down trees, Derb, but luckily I can trim. I looked for the  "a short antenna that works" thread, Slab,  and it didn't come up, but I've got the picture. One of the best antennas I've got is the 18HT "High Tower". I've got a 5" loading coil for 180 meters that works well. It's great on 80 for DX, but the problem is receive. During a skip cycle I had a QSO with a guy in Australia, on 80 meters, he could hear me but I had to get a relay from someone for the reception. Right now the 18HT is down due to too many branches. I'm trying to get the tree guy out for that.

I have two lots and the longest point is diagonal across both lots ( 140 feet), In the back of the lots there is a 7000 volt line running on top of the power poles. I dare not get close to that (I wish they'd bury the darn thing). By hook or crook I'll get something up.

TNX de Gary,KF9CM