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#1
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40M HF antenna suggestions
With the downturn in the solar cycle and worse days ahead, I'm faced
with operating on the lower hf bands. 20M has gotten to be very hit or miss wrt propagation and it seems that more and more dx is happening on 40 (with some on 30). I have a 40M dipole up about 30 ft or so, but that really doesn't cut it. I know that this is like a discussion about "what's the best color", but what antenna systems will work well on 40M, maybe even 80M, that I could mount either on the ground or up no higher than 30 ft? I need to at least get some general direction on this from an experiential data set rather than starting with the ads in QST or CQ. Tnx - Mark Sheffield/N0LF |
#2
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Hi
One possible could be ground mounted vertical array. There are triangle and quad (four "corner" ) constructions. Triangle gives 6 switchable directions and some gain and FB but requires radial wires to be effective. QST Aug -72 had a quite extensive article of 7MHz triangle array. 73 Kari B Mark Sheffield wrote: With the downturn in the solar cycle and worse days ahead, I'm faced with operating on the lower hf bands. 20M has gotten to be very hit or miss wrt propagation and it seems that more and more dx is happening on 40 (with some on 30). I have a 40M dipole up about 30 ft or so, but that really doesn't cut it. I know that this is like a discussion about "what's the best color", but what antenna systems will work well on 40M, maybe even 80M, that I could mount either on the ground or up no higher than 30 ft? I need to at least get some general direction on this from an experiential data set rather than starting with the ads in QST or CQ. Tnx - Mark Sheffield/N0LF |
#3
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If you have the horizontal room (70 feet, sounds like you might) and
at least 35 feet up, why not a Half Square for 40? Doesn't need radials, it's an 'upside down' phased vertical array with some gain and a good TOA. Be aware however, it is somewhat directional. Easy to make on your own, also cheap and there is a lot of info on the Web. I have one for 20 meters (very modest with the antennas here) and it works a lot better than my R5 vertical and full sized G5RV. |
#4
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A horizontal Loop at low elevation can be an effective low angle radiator
when it is more than 2 wavelengths around. I had a loop running around trees in my yard, irregular shape and random length (210 feet), fed it with 300 ohm tv line. It worked quite well. At its highest point it was under 30 feet and it was at 20 feet on two corners. I even loaded it up on 160 and worked both coasts from here in Chicago with 100 watts. Read up on the topic at http://www.cebik.com/atl1.html He has lots of other interesting antenna articles on that site, just stop the address at the com/ to see the list. KA9CAR John "Mark Sheffield" wrote in message ... With the downturn in the solar cycle and worse days ahead, I'm faced with operating on the lower hf bands. 20M has gotten to be very hit or miss wrt propagation and it seems that more and more dx is happening on 40 (with some on 30). I have a 40M dipole up about 30 ft or so, but that really doesn't cut it. I know that this is like a discussion about "what's the best color", but what antenna systems will work well on 40M, maybe even 80M, that I could mount either on the ground or up no higher than 30 ft? I need to at least get some general direction on this from an experiential data set rather than starting with the ads in QST or CQ. Tnx - Mark Sheffield/N0LF |
#5
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Mark,
You're not going to like my suggestion but here goes...try a vertical. Ask around, the people with the poor ground systems and those that have never used one will condemn them. Those that have used them with good ground systems will praise them. 73s, Evan |
#6
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If you cannot convince yourself to put in the pile of ground radials,
you can use an ELEVATED 40 meter vertical. You can SHUNT FEED it so that it does not require an insulator, making the whole affair solid grounded to boot. Your radials should be a minimum of 9 feet up off the ground. You may make the shunt section out of six inch TV twin lead stand off mast clamp spacers, and use not much of a spacing for the trimmer capacitor for the gamma match that feeds it. You will find that you can take about a three foot section of RG-8 coax, and turn it into a capacitor by connecting the shield to one side of the coax feed line and the center conductor to the gamma match wire section which you make out of ordinary copper wire or whatever. Put a couple turns of hard copper ac wire around a screwdriver handle. Put that across a common antenna insulator as a two turn coil. Connect that in series with an elevated radial. Stick a grid-dip oscillator in the middle of that little loop and tune the radials to reasonance by shortening them from too long to your target frequency. Adjust the length and the gamma match deal with an AEA or other antenna analysis unit for flat SWR at the coax feet terminal for your project. Using the totally grounded method described lets you go down to the base of the pole and make SURE that it goes to a good ground rod. Use a few short six or eight foot radials at ground level to create the drain for any direct lightning hit you may take. The idea works very well from experience and more than one hit. Run your coax feed line for the affair to the base as well and thence into the shack, using techniques that ground it well too, plus proper interface lightning suppression where the coax comes into the shack as well. Here in the W5 call area, with a KW against it and a good receiver, on CW in either the CQ-WW or the ARRL CW DX test, I've consistently been able to pile up between 80 and 100 countries in any given contest .. often as many as 400-500 plus 40 meter QSO's. By using flag pole techniques you can make it look as neat as a pin for the inquisition .. grin. If you have noise problems, you can help that with the new cancellation RF devices. As well, you can also design the thing so that you can cover 80 meters too! The way to do that is to create the main vertical element so that it also has a folded loop operation all the way up to the top and down. On 80 you feed it is a folded monopole. On 40 you short that folded monopole at the base ,, a presto you have you full length 40 meter element with a wider element profile, that is all. Proper use of a Rohn 25-G few sections and a concrete ufer style base can get you a completely self-supporting element for the basic contruction. The neat part of this is that you can go inside that tower and run additional coax up it to get a small VHF antenna or dish up there. Or you can also side straddle mount a little Wireless 802.11 paddle or dish up there and PRESTO, if there is an IP wireless service, you can run that or whatever through, say, CAT-5 inside the tower .. and instant high speed connection for you as well. Just bring the internal lines down the inside of the tower and do the lightning mitigation work at the base for them as well. Yes, you'll have to adjust the tower height to account for the effect of whatever other metal mass is up there for stunts like this, but you *CAN* do it and do very well on 40 and 80 too! Plus if you get bold. you can get a full sized 80 meter stick up there with Rohn 25-G and a galvanized mast stinger on top which works just as good on 80. But you'll have to use guy wires and so on for the elevated version, which of course has those longer elevated radials as well. It's neat as a pin, terribly structurally efficient, and works a heck of a lot better than any horizontal affair you are likely to get up in your restricted space. W5WQN .. Mark Sheffield wrote: With the downturn in the solar cycle and worse days ahead, I'm faced with operating on the lower hf bands. 20M has gotten to be very hit or miss wrt propagation and it seems that more and more dx is happening on 40 (with some on 30). I have a 40M dipole up about 30 ft or so, but that really doesn't cut it. I know that this is like a discussion about "what's the best color", but what antenna systems will work well on 40M, maybe even 80M, that I could mount either on the ground or up no higher than 30 ft? I need to at least get some general direction on this from an experiential data set rather than starting with the ads in QST or CQ. Tnx - Mark Sheffield/N0LF -- -- Sleep well; OS2's still awake! Mike Luther |
#7
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Thanks for all the replies and suggestions, both to the group here and via email. Just about all the suggestions have been to go vertical in on manner or another, and this I will do. Thank you all - Mark Sheffield/N0LF |
#8
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Two suggestions:
1. Try EZNEC antenna modeling software (or buy it, NEC 3.0) and model all kinds of antennas. 2. How about a dual "H" config dipole? It concentrates radiation in two directions and is low TOA. Bob K9KKY |
#9
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Bob - never heard of a dual H. Is there a reference for it so I can read up on it? tnx - Mark/N0LF On Wed, 3 Sep 2003 18:13:55 -0400, "Bob Cook" wrote: Two suggestions: 1. Try EZNEC antenna modeling software (or buy it, NEC 3.0) and model all kinds of antennas. 2. How about a dual "H" config dipole? It concentrates radiation in two directions and is low TOA. Bob K9KKY |
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