Posted: 5/9/2012 7:07:00 PM EDT
Okay, it's actually a rotatable dipole, and I'm very pleased with it! 
I had reached the limits of my Hustler 6BTV with 32 16.5' radials (40 and 80 top part removed) and wanted something better since I couldn't fund the 50 - 60' tower and tri-bander this year. Got the MFJ-1769 aka Hy-Gain TH-1 and mounted it on a 10' mast with a Radio Shack rotator and tripod on top of my house. It's about 26' above ground and I live in a somewhat low spot. Covers 20-15-10-6 and was easy to tune for good SWR across most of all of the bands. Received signals are up to three S units higher than my vertical on HF 95% of the time for both DX and domestic stations. Pretty much always 2 S units better on the dipole. The only issue I had with the antenna is that I stripped out three hose clamps trying to get the elements tightly together. They only slit one side of the tubing from the factory and the thicker stuff wouldn't get tight enough before the clamp gave out from too much stress. I fixed that by putting a second slit on all of the sections. I still may put a stainless steel screw through all of the joints for good measure. The antenna is 1 sq ft wind load and with the 26' length it will be fun to see what part gives out first when we have the next big storm. The mast is 1" SCH 40 galv pipe and I'm betting that the rotor spins before the rest goes. Still hasn't helped with Yemen or Somalia but it seems to work well. HFTA graphs for it look really good. Just worked Tajikistan on CW first try in a pile-up! 
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Thats cool! I use the driven element from a Mosley TM-33 and have it mounted on my roof tripod's leg. Mine is fixed in position, but works. I don't have room for the whole Mosley, the rest of it is in my living room.. How much signal difference is there when you rotate it 90 degrees from the station you are listening to?
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Quoted:
How much signal difference is there when you rotate it 90 degrees from the station you are listening to? The specs say 20 dB but I've found it varies a lot depending on the station I'm listening to. The most I've seen is probably around 4 S units or so, or not much more than 15 dB. I've spent more time aiming it and then comparing it to my vertical, but I'll pay more attention to this now. I tried at lunch today but the bands are in bad shape with too much QSB to compare. |
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Quoted:
The most I've seen is probably around 4 S units or so, or around not much more than 15 24 dB.
FIFY. Those confusing dB's and S meters! Shouldn't try to rush math over lunch hour.
I have no excuse either, I'm using a Flex with a calibrated meter that reads in both dB and S-units. Just checked it again and it's over 20dB down on the null with 7O6T on CW. ETA: I gave up on him but did just manage to work Kuwait!
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Quoted:
Quoted:
The most I've seen is probably around 4 S units or so, or around not much more than 15 24 dB.
FIFY. Those confusing dB's and S meters! Shouldn't try to rush math over lunch hour.
I have no excuse either, I'm using a Flex with a calibrated meter that reads in both dB and S-units. Just checked it again and it's over 20dB down on the null with 7O6T on CW. ETA: I gave up on him but did just manage to work Kuwait! Well, that made up my mind. I going to take down "Robo-tenna" 
and put my driven element up on the rotor. I didn't realize there was that big of a null on a "rotatable dipole" so-to-speak. Thanks for the info..and new project..
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That looks like a good setup, how well does it work? My neighbor does satellites and would love to have something like that!
The effect of the null on the sides of the dipole varies a lot. The closer and stronger the station is, the less you notice it. My neighbor has his antennas less then 500' from mine and with him running 5W and me 1W on 10 meters we both noticed no difference on the dipole orientation. Noticeable changes on strong US stations, but not 20 dB. It's on the weaker and farther stations where you really notice it. S9 on the good side, down in the noise in the null. The good side is way better than my vertical and I've worked Jordan, Kuwait, Yemen, and others that I couldn't do with the vertical. Couldn't hear them well or reach them before, now I can. This will keep me happy for some time but I'm looking forward to upping the performance this much twice again next year with a 3-element Yagi over twice as high! |
I did some measuring this evening. My driven element is too long to rotate. It will hit my other mast. The Robo-tenna works well as far as gain and directionality, but a PITA to steer. It is all manual control (with rotor control boxes) as there is no computer interface to help. I tried for a while to work the ISS and AO51(?) to no avail. I could hear them, but between adjusting rotor boxes hunting for the birds, then messing with the VFO's for Doppler it was way to complex for a normal human.
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Quoted:
I did some measuring this evening. My driven element is too long to rotate. It will hit my other mast. The Robo-tenna works well as far as gain and directionality, but a PITA to steer. It is all manual control (with rotor control boxes) as there is no computer interface to help. I tried for a while to work the ISS and AO51(?) to no avail. I could hear them, but between adjusting rotor boxes hunting for the birds, then messing with the VFO's for Doppler it was way to complex for a normal human.If you can rotate the element 90 degrees that's really all you need. Mark some spots on the rotor control some how. 73, Rob |
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Thanks for the compliment, Mojo.
You'll need to be able to rotate 180 degrees to cover the full 360. I keep the rotor "homed" on South and rarely take the dial past E or W. If you only rotate 90 you'll only to point to half of the compass. Since the beamwidth is so wide though, you could actually get by with a little less than 180 if you had to. |
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Thought I'd bring this thread back with an update before it goes to the archives.
The new dipole is performing so well, and the vertical so poorly compared to it, that I plan to remove the vertical soon. We've had a dry Summer which hurts the vertical, but even this Spring when it was wet the dipole almost always won. No sense mowing around something I never use anymore. I thought about keeping it for diversity on the 2nd receiver but signals are just so weak on it. 99% of the time the dipole receives 2 S-units better than the vertical. Transmit seems better too. I just worked a ZL2 on 15 with the dipole that I couldn't even hear on the vertical. I've seen that same thing over and over. Hopefully I can get the Yagi I want next year up 50 - 60' and be so amazed that the dipole goes then too! ETA: I also notice a lot more QSB with the vertical than the dipole... ETAA: A little less noise on the dipole too And I just worked E40VB on the dipole!!! |