I just built this 40-80-160 trap dipole (from qst and arrl antenna book)http://www.dxzone.com/dx13248/trappe...60-meters.html for the limited space I have.The total length is about 124 ft. . It had decent swr on 1.8-2.0 but I have yet to find time to finish getting 40 and 80 tuned right . This is my first project beyond the standard dipole so I'm still not sure how affective this antenna will be
NVIS for 160
I have a drooping dipole - feed is coax at 30 feet and the ends are at 15 feet. Works FB out to 5-600 miles. Most of the time I use 100 watts on LSB. This winter, if it wasn't for 160 meters, there would have been very little evening conversations with locals.
re: 160M antenna ideas wanted
Originally Posted by WC4R
I agree with the replies by kl7aj, WB3BEL and KD7MSC.
You would appreciate the book by ON4UN, John Devoldere about low band dxing, even if you're not interested in working DX.
And, w8ji.com is a wealth of the most accurate information about 160 meter antennas you will find anywhere. You CAN trust ANYTHING you read there. Tom is a genius. He knows exactly what he is talking about, and major manufacturers of ham equipment and antennas pay Tom top dollar for his expert advice.
If you have the space, you should consider a couple of 580' long 2-wire bi-directional Beverage receiving antennas. I have one so far (SW-NE), and it is a "magic" antenna! On a scale of one to ten, it's "wow factor" is an 11.
Unless you want to work only stations very close to you, use a 1/4 wave vertical, an inverted L, or a T antenna with about 60 1/4 wave radials. Use Beverage antennas for receiving.
Last edited by W0BTU; 03-02-2009 at 01:27 AM.
160m antenna ideas wanted
Originally Posted by KI6PSU
I'm sure it would, but as you move the loading coils out toward the ends, they require more turns.
Also, this antenna (and it is not my design, just a sketch I found online) is supposed to work for both 160 meters AND 40 meters. The inner portions of the legs are resonant on 40 meters, with the coils choking off the outer segments. If you moved the coils, that would ruin tuning of the 40 meters part of it.
What I want to see is if the 40 meters inner segments will still work 15 meters as I do now with my 75-40-20 meter multidipole. Legs are 58'-58', 32.4'-32.4', and 16.4'-16.4'.
I was thinking of replacing the 40 meter legs with the 160-40 in this sketch. That would give me coverage from 160 m - 6 m, instead of the 75 m - 6 m I have now.
I really don't have room on my lot for a 246' dipole. I have to shorten it with loading coils.
Physics is a real, uh, problem, huh?
Shortening a 160 meter dipole by 50% presents a whole bunch of problems that are not easy to solve. Considering the antenna in the diagram with loading coils at the 50% point, the feedpoint impedance of the antenna should be close to 25 ohms with the antenna in a flat top configuration at 50 ft. and assuming you wound a coil with a relative good Q (resistance about 4 ohms). Now you need a matching network.
Once you match the antenna, the 2 to 1 SWR bandwidth should be about 11 kHz. You could get more bandwidth by winding a low Q coil that would burn up a lot of power but that is not a good choice. If you move the coils closer to the end it will decrease the bandwidth some, as well as make the coil construction more difficult. If you place the coil right at the feed point, you could increase the bandwidth to a whopping 12 kHz, but that drops the feedpoint impedance of the antenna to about 14 ohms.
It's also easy to wind a coil that will dissipate a lot of your power. With the coil mentioned above located at the 50% point on each leg, the coils dissipate approximately 37% of the applied power. The one located at the feedpoint could have less resistance because it requires less inductance but because of the higher current, the coils will dissipate about 44% of applied power. These coils are fairly easy to wind on a PVC form. You could wind a lower loss coil using an air form which would dissipate a lot less power, but the bandwidth of the antenna will go down significantly and so will the feedpoint impedance.
It's not an easy design. But you can make it more complicated by trying to make it work on two bands. In order to do that, the coils have to be at about the 50% point and they have to be self resonant on 40 meters. It just so happens that one wound on a PVC form should come very close to that. So you need a coil that has a low frequency inductance of about 87 uH, and a distributed capacitance of about 5.9 pf. That should be close. Some pruning may be required.
Oh, and the matching network probably won't work on two bands, so you may have to go with a tuner and accept a minimum SWR of 2.0 on 160.