200' Doublet - The Hook Up

First things first. Before you drill holes and whack out expanded steel with your grinder, as I did, move your gear to a safe location. Or, if you're lazy like me, just use a drop cloth. 



Once the drilling and cutting was done, I ran PVC pipe through the holes and inside that some 1/2" flexible tubing to center the wires and to provide some strain relief going in and out. I'm not grounding the feed line, but did insert a heavy duty cut-off switch on the outside wall.




Where the ladder line drapes under the eave before entering the shack I added a short standoff to keep it a foot or so from the metal frame of the fascia and to provide a bit of support for the 35 feet or so of line leading up to the antenna. 

 

Inside the shack the ladder line goes directly to the Johnson Matchbox "Lite", with no intervening balun, and it seems to work fine. I haven't yet noticed any RF side-effects, but I haven't run more than 40 watts through it so far. The second tuner is a homebrew unit I obtained from G3VKM years ago. It is a simple L-C tuner that can also be configured in a serial arrangement. It's not quite up to that task of tuning random wires and doublets as the Johnson unit is, but it works well enough. I have it now hooked up to the 400' Loop. The tuners are required for the Ten Tec Scout since it has no ATU built-in (never did, never will). 

An arrangement of coax switches brings the tuners' outputs to either the Scout or the currently in-repair K2. This allows me to A/B antennas for a single rig, and to A/B rigs for a single antenna. It's a bit awkward for the K2, however, since it has its own ATU, but its a workable configuration for now. The coax bypass switch in the upper right of the photo is not in use at the moment, by the way.

 
I made up a spreadsheet for easy reference to the manual tuner settings for both the Loop and the Doublet. I initially made it thinking I was going to only use the Matchbox, but the addition of the open-wire feeder made that impossible without adding some more external switching, which I think would be over-kill, so I brought out the G2VKM instead.

The Loop is pretty amenable to all HF bands hooked up direct, but the doublet looked a little hopeless on 30 through 80 meters at first. The Johnson brought down those high SWRs just fine, though. The highlighted entries are just notes that those particular bands could be handled direct if I had a bypass switch in the tuners or externally. Note that the G3VKM really doesn't help enough on the 30 meter band on the Loop, but it's not terrible. 

Once it was all hooked up I did some A/B reception tests and the doublet is clearly louder by about an S-Unit over the Loop. The Loop, as loops should be, however, sometimes had the edge because of a better S/N ratio, but generally signals came through more readable on the doublet. 

We went for a 3 day trip up to Lake Arenal right after I got this all connected, so I didn't get a chance to try out the doublet on TX until this afternoon. Though I didn't do any A/B QSOs with the two antennas, the doublet was performing very well into Europe today on 30 meters. I didn't give it enough time on 20 meters, only working a couple of Stateside stations on that band. It seems that it's going to be a satisfactory antenna and I'm really looking forward to giving it a more thorough shake-down when the K2 is back in operation. If it turns out that the Loop is only useful in a small number of QSOs then I may convert it to a second doublet with a different orientation than the new one, fed also with open line, of course!

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Thanks very much for your comment! 73, Casey

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