I am thinking of using two 40M hamstick antenna mounted horizontally and feeding it with ladder line with a tuner to work 40 - 10 meters just like a wire dipole. Any thoughts. W6STU
Yes. 1) It will work. 2) It will radiate skyward (straight up, more or less) unless your attic is about 60 feet or more above ground. 3) Lots of better antennas than that---look into stealthy outdoor verticals, for one. 4) Any attic antenna is always prone to RFI and coupling to house wiring, metal ducting, downspouts, etc. 5) See point No. 3
Inductively loaded antennas are primarily single-band antennas because of lossy self-resonances at the higher frequencies. They don't work "just like a wire dipole". A 40m hamstick dipole is not an efficient performer even on 40m. If I had to settle for a hamstick dipole, it would be for 14 MHz and above.
If you're going to feed it with ladder line, why use the hamstick dipoles. Simply running wire antenna elements would be less expensive without the self resonance issues Cecil mentioned above. How much linear space do you have to work with in your attic? And of course are you limited to the attic by HOA rules or is there any possible way to get the antenna outdoors? If you must have the antenna indoors then make the best possible use of any available space.
A 40m hamstick dipole antenna will work OK on 40M but the inductive loading and feedline loss will make it very VERY inefficient on other bands. A tuner near the radio may be able to give a low SWR AT THE RADIO but will not make it radiate any better on any band but 40M.
The term "work OK" is naturally subjective. "OK" for one may be "NOT OK" for another. A 40m hamstick has a radiation resistance of around 3 ohms. Divide that by the feedpoint impedance to get an estimate of efficiency. A fixed antenna location almost always has more space available than 16 feet. High-Q loading coils and top hats will increase the efficiency and more than double the radiated power vs a hamstick dipole. An 80m or 40m hamstick dipole will result in close to QRP levels of radiation from a 100 watt transceiver. That's NOT OK for me but other's mileage may vary.
Here's something to think about... A full sized 20m dipole will outperform a 40m hamstick dipole, when the 20m dipole is used with an antenna tuner on 40m.
We did a show-and-tell at a school one day -- one guy brought a home-brew 20m hamstick dipole and a 100-watt radio. I brought an 817 and a Buddistick, tuned for 20m, which I clamped on a fence. I heard more and worked more with 5 watts, than he did with 100 watts.
I use ham sticks as my 'emergency' antenna. When there's a storm brewing and I have to lower my main antenna, I mount my hamsticks (one at a time of course) on an Outbacker Outpost tripod. ( http://www.outbackerantennas.com/outpost.html ) This setup does a pretty good job, and would work better than a dipole in the attic. If you attach a counterpoise that is (180/freq MHz) to the base, you'll find that the SWR will come right down to where you want it. You're basically creating a monoband ground-mounted vertical. Setup/breakdown time is about 5 minutes, and you can leave it out until someone complains. Most HOAs cannot do anything about a temporary structure, but if they complain, break it down, and put it back up the next day. The only disadvantage is that you have to go outside and change the antenna and counterpoise length when you want to change bands.
I did some research on this as the idea sounded interesting. I'm not an antenna builder, I just have some theoretical knowledge from studying electrical and computer engineering in college, and in reading some on antenna building. So I may not know what I'm talking about. First thing I see as a problem is the feed line. The dipole is going to have an impedance somewhere between 50 and 75 ohms, and if close enough to the ground the impedance will be even lower. Using 450 or 300 ohm ladder line just sounds like a bad idea. Use coax instead. No need for a balun but if you have one then it wouldn't hurt. But then if you are going to buy a balun then get one that suits the antenna and feed line you want to use. If you really want to use twin lead feed line and not need a balun then lamp cord, speaker wire, or doorbell wire. Doorbell wire comes in a twisted pair and might be better than the others, but it's generally pretty light gauge. Lamp cord and speaker wire will have an impedance of about 100 ohms, and be a bit lossy (perhaps an understatement), but that's likely better than the impedance mismatch you'll have otherwise. If you want something that works on 10 meters then just build yourself a dipole. A folded dipole made from ladder line will be about 17 feet long. Looking up the length of a 40 meter hamstick and I see that they are 7 to 8 feet long. If you have room for two 40 meter hamsticks put end to end then you have room for a half wave 10 meter dipole. A folded dipole fed from ladder line is about as perfect match as you'll ever get. Cheap too. As long as I've brought up lamp cord I'll mention that people have made cheap and effective 10 meter dipoles from just lamp cord. It might take some experimentation to trim it right, but it's cheap and easy. There's even some hints I've seen in tying a knot at the center to keep it from zipping apart further after being hung. The lamp cord will have some loss as the feed line but if you aren't running much line and want it cheap and simple then this works. I'm sure that there's a lot of people just wincing at the idea of building an antenna out of lamp cord. That's fine, it's not an ideal solution. I'm just thinking a lamp cord 10 meter dipole would perform better on 10 meters than a dipole made from 40 meter hamsticks would perform on 10 meters. I'd like to model this hamstick antenna when fed from ladder line to see how it would perform on 10 meters. I'm guessing the hamsticks would make for an expensive capacitance hat for a monopole made of ladder line. Then again, as I said earlier, I may not have any clue what I'm talking about.
