The 160/80 antenna saga

Long story and long overdue (but who’s waiting anyway?) but here it finally is: the long and extended and most of all never ending story about my new 160/80m vertical antenna.

"In the past", being from summer 2006 up to now I used a "shorty loaded dipole" on 160m. It was an old 80m dipole loaded with coils made by Hy Power Antenna Company. My goal was to work local mults in contests like CQ WW and RDXC. I knew this antenna wasn’t going to kick ass but I must admit that out turned out to work way better than hoped for. The thing is suspended by a rope on a pulley on the top of the tower but can only be deployed if the tower is at least up one level. Simple trigonometry teaches that the dipole is too long if the triangle’s top is too low.

On 80m I used an elevated ground plane antenna. It was built from heavy duty aluminum telescopic tubing with on top of that about 7m of fiber glass fishing pole. The feed point is 4m above the ground and is connected to two tuned elevated radials. A wire went up for about 10m and then another 10m run horizontally. It was basically an "elevated inverted L with 2 elevated radials". Now this antenna rocks! For its simplicity and price, it can’t be beaten. I worked tons of nice DX on this one. But the WX needs to cooperate. Due to the location of my lot and the specific setup, it can’t be guyed. I don’t want to bother the land owners around me. So if the wind blows a tad too hard, the antenna shows odd behavior (remember the Lambada?). During CQ WW CW 2007 I needed to adjust the position a couple of times during nighttime due to increasing wind speed and changing direction.

Regular readers know that WX hasn’t been kind to field day style contesters in 2008. Even when the wind blows considerably, I can crank up the tower. So I have the yagi and 160m and a 40m GP. But the Achille’s heel of ON5ZO is 80m. Wind means no 80m. No 80m means no contest. So I had to do something. I cannot put 80m on the tower together with 160m, so I came up with the following idea…

  • Forget existing 80m and 160m antennas.
  • Run an inverted L as high up the tower and far away as you can. Add some more elevated radials.
  • Use matching device at feedpoint to trick amp into 50ohms.

This had the following consequences (pro and con):

  • No more flimsy 80m vertical = independent of the wind. Practical construction shows that this is the case.
  • Go vertical on 160m = more chance to work DX. Proven in last CQ WW CW. Easier to work USA and got called by ZY7C for a new DXCC on 160m.
  • No more retuning antennas from CW to SSB for the occasional phone contest. Small benefit but you never know.
  • Sacrifice 80/160 monoband operation for SO2R. This hurts, as I witnessed in last CQ WW CW. Learn to live with it for now.

The plan had been ripening for a few months. Only unknown parameter was the matching device. I’ve been lucky with an SGC-230 in the past but it is rated 200W and I need beefy QRO ratings. All stuff that matches weird impedances to 50ohm all by itself and handles 1000W or more is either homebrewed or extremely expensive. I’ve got more time than money so homebrew it is. Then along came a bargain and along went the bargain, read all about it here: Garage Sale @ ON5ZO. Return to zero then…

One day I was talking this over with Wim ON4BHQ = OQ4B and he told me that he was about to lay his hands on a good-as-new MFJ-998. I am not familiar with MFJ other than their questionable reputation but I was very intrigued by this device. It looked like it was what I needed. My only problem: I could not put the tuner in the shack because of my setup. I run with two feedlines from the shack to the garage. There is my antenna switching box. I don’t want to run my coax and relays with high SWR under high power and the tuner has to be on the dedicated coax for 80/160. If it’s in the shack, I need to switch it off when not on 160/80 etc etc. So I contemplated and decided that "remoting" it should work as the tuner automatically tracks bands and searches a match.

I waited until Wim got his and invited myself over to check it out. Wim said that the auto-tuning works fine except after a QSY you sometimes need to hit the tune button. That would be impossible in my case since it will be in the garage where it’s out of reach. I decided I needed to plunge into the unknown and just order the MFJ-998. CQ WW CW was approaching WARP 6… The box arrived short after ordering from a German distributor and I quickly hung up the 80m inverted L. On the tower this time, not on the wiggling aluminum tubing. I could find a match on 80/160. Next up: try to match it with the amp. Or rather: match the amp to the match found by the tuner. That didn’t work at all. I could turn the dials on the ACOM amp but never would I reach a match. I discovered a water soaked coax jumper could be the culprit. I anticipated on having it all ready the Saturday before CQ WW CW to try it out in the LZ DX contest. No go, read it here: Countdown to CQ WW CW speeding up.

So I tried numerous and countless things to get it working. I was lucky to that Peter from offered prompt support and sent off a couple of current chokes optimized for the low bands. That problem was solved. Now I encountered the problem ON4BHQ described: after a QSY, no match was found automatically and you need to hit the button that starts the tuning sequence. How much troubles can you have? I’ve built numerous antennas in the past but none were so hard to get working. But quitting was not an option with CQ WW CW starting in less than 48hrs. Desperate measures for desperate situations. I drilled a hole in the tuner’s bottom plate (bye bye warranty) and routed a small cable through the hole. I soldered the cable across the pins of the tune button. I used a free pair in a multi-wire running from garage to shack and soldered a push button on the cable’s shack end. There you go: I could now remotely tune the thing. I exchanged a few emails with MFJ prior to this. They were pretty responsive. It seems that a genuine remote controller is in the works for the MFJ-998. They already have one for the other models of automatic tuners.

Now I tested this setup with the tower 2/3 up and there was no problem on 160m. That worked. However on 80m I would get ‘arc faults’ on the amp as soon as the key down level exceeded 500W or so. This would happen in the CW sub-band (lucky me with a CW contest coming up) with key down for a few seconds in order to find a match and write down the values in my tuning table. This lead me to further investigate the antenna, re-attach radials etc – yet another complete revision of the antenna. In the cold. In the rain. Once more. I’ve had arcing errors in the past and usually it tracks down to something in the antenna system. But this time the antenna seemed OK. One thing I had noticed when opening the tuner to solder the wire, is that it was rather warm inside. Not hot, but too warm for a) temperatures in the garage and b) the power levels applied. So maybe this specific setup on this specific frequency resulted in such a combination
that the capacitors would break down?

The solution seemed simple: use very low drive levels to match the amp and then increase the drive. I could then match the amp on both bands and get 900W out without a problem while sending CW. Not key down of course because then the arc errors would show up. I never run more than 900W anyway. The next day I cranked up the tower until it was fully extended. My fear was that by raising the vertical part of the L and shortening the horizontal part, a lot of new problems would show up. But it didn’t. The antenna did its work on both of the lowest bands and never did I encounter an ARC fault and my extended tuning table with values every 10kHz was every accurate. I was very glad and I intend on looking of a weatherproof plastic housing to put the antenna tuner outside and eliminated the 10m coax from garage to feedpoint.

But I told you this is a never ending story. Yesterday I cranked up the tower to 2/3. Guess what: no problem on 160 but arc faults on 80m galore. There must be something with this particular setup on this specific frequency that makes the tuner act weird. To be continued (unfortunately)…

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