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auto coupler with whip and coil?	Reply
by KC2RGW on September 25, 2008	Mail this to a friend!
Has anyone ever run the following SGC 237 auto coupler 3' solid mast high Q coil 102" whip I've got the coupler and whip now, but it's essentially a dummy load for 80m and not much better with a 3' mast extension under the 102" whip for 40m. I was pondering putting a coil at the top of the mast just over the roof of my Wrangler with the whip on top of that to increase efficiency for 40m and 80m. My hope would be to get more optimal efficiency for 40/80 and remove the coil if I wanted to work the upper bands again.

RE: auto coupler with whip and coil?	Reply
by K0BG on September 25, 2008	Mail this to a friend!
You can do this, but you have to make sure the coil's self resonant point is well above the highest operating frequency. Go to my web site, and look under Auto-Couplers for more details. Alan, KØBG www.k0bg.com

RE: auto coupler with whip and coil?	Reply
by AA4PB on September 25, 2008	Mail this to a friend!
My guess is that if you have that poor of performance with the SG-237 and whip then there may be other issues like proper grounding or antenna location. You are not trying to use coax between the coupler and the whip I hope. I use the same SGC coupler and a whip mounted on the lip of the bed of a pick up. I can work around the state on 75M and much of the country on 40M in the evening. I certainly don't find it to be a "dummy load". Surely its not as efficient on the low bands as a good quality, properly mounted screwdriver but its a heck of a lot more convenient.

RE: auto coupler with whip and coil?	Reply
by KC2RGW on September 26, 2008	Mail this to a friend!
No, it's wire fed with about 8" of 6ga wire to the whip. I can make contacts, but it's far from being efficient. It's just simple math, I'm tuning 102" for a band where a quarter wave is 66 feet. The losses are massive. On the upper bands I can make contacts much more easily with a quality signal. On 40m and 75m the signal is so weak it's just not worth pestering people with contacts. I like to rag chew and there is nothing worse than trying to have a conversation with a marginal signal. An example, there is a guy running 40' of end-fed wire in an attic that tries to make contact on 75m. He's also afraid of running his 100W radio at 100W so he runs it at 40W instead. He gets frustrated because nobody can keep a contact going on 75m with S9 static crashes when he is S3 at best. I never want to be that guy.

RE: auto coupler with whip and coil?	Reply
by AA4PB on September 27, 2008	Mail this to a friend!
Granted there is a lot of loss in a 102-inch whip on 75M. Even the best screwdriver is only a few per-cent efficient on 75M. When you say the antenna is a "dummy load" I'm thinking that you can't make a contact more than a few blocks away and I find that they work a whole lot better than that. If you put a coil in the middle of the 102-inch whip then you still have a 102-inch whip and the same math applies. You have moved some of the required loading inductance out of the tuner and into the whip coil so you could reduce the losses a little if you use a good quality coil. If you make the inductance large enough to make the antenna a center loaded self-resonant on 75M then the base feed impedance will be around 25-Ohms and an easy match for the tuner. If you want to make a major improvement on 75M then you need to lenghten the whip considerably. If you double the length then the radiation resistance is 4 times while the loss in the tuner is likely reduced as well. Now you probably can't drive around with a 16-foot whip but it would be possible for stationary mobile operation. I think MFJ still sells a 12-foot telescoping whip or you could make something you could assemble from small sections of tubing.

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