Or “The horror of QRO and extreme antenna impedances”. Last year I started dabbling with an MFJ-998 auto tuner for a 80/160m antenna. Loyal readers might remember I spent numerous hours (days!) changing everything to get it right. As it turned out the MFJ automatic antenna tuner doesn’t like currents on the coax shield. That drives the device nuts. Which in turn drives the operator nuts.

I tried adding coax choke baluns everywhere but to no avail. I finally added a homebrew monster current choke. Refresh memory here. The link shows a picture of the inside.

Today I opened up this balun to replace the M4 bolts with a sturdier M6 size bolt. The horror! I used pieces of glue gun sticks to keep the stack of ferrite cores in place. Where the wires touch this glue, it was molten. The wire is kept tightly wound around the cores by means of white cable ties. Where it touches the wires, they’re turning slightly brown. Conclusion: things must have gotten pretty hot in there.

Now what? I really do not want the mayhem to start all over again. That bloody antenna with the MFJ needs to work and stay working like it did after I added this choking balun. There are several options from here.

1. See no evil, hear no evil. Just close the box, put it up and play at maximum volume. Will it work with the new radial arrangement? Will it stay in business? Will the wire insulation melt and short out the whole shebang? The question is whether the heating came from a “one time only” failure or do the wires become too hot when using the antenna for too long?
2. Replace the homebrew unit with a commercial one that is rated 2 kW or more. DX Engineering sells one (link) and Balundesigns has one too (link). The price is right when you consider the parts. My home made choke uses a stack of 5 cores costing 10 Euro (14 US $) each. The problem is that shipping costs 35-40 US$ with the chance of a zealous customs officer picking out my parcel and charge me import duties. On top of the the added cost, this procedure will then delay the delivery of my order. Hence this option is not really attractive.
3. Replace the 1.5mm² wire pair with thin high quality Teflon coax. I’ve seen some examples that use this coax rather than simple copper wire. The copper wire’s insulation is rated x Volt, with x being a number I don’t know by heart but it certainly isn’t rated for extreme voltages that might occur with the extreme impedances the antenna exhibits under a kW load.
4. Redo the whole thing myself using a combination of more ferrite cores (100?) over the coax and use the QRO rated Teflon coax. Then add the reengineered balun with the copper wire replaced by this same Teflon coax. Approximate cost with DX-Wire stuff is 78 Euro ex S/H. Better safe than sorry and knowing this antenna / MFJ thing combo needing A LOT of choking impedance, this overkill scenario seems the way to go. Especially since I had quite some fun on 160m last winter. Presumably the coming winter will be Low Band Time again, so the bloody thing needs to work and keep working.

Stuff to think about…

• Coax switching mess almost cleared around the microHAM relay box.
• Yesterday the Big Yearly Total Thoroughly Cleansing of the shack. Found a few stacks of QSL cards which I’m not certain that I’ve processed yet. Plus a BIG box I definitely still need to process.
• Let amp run dry and have XP install yet another bunch of updates.
• Just tested all bands on the tower: 30m to 10m = all systems go!
• Bought bits and pieces plus odds and ends to connect coax in outdoors cabinet.

So I finally could actually make a QSO soon. I’ve been reading the new G3SXW book. Fun reading, I might reread his other books one of these days.

I’m contemplating to get rid of the shack’s USB mouse and PS/2 keyboard. Replace with QRO-proof 2.4 GHz stuff? People recommend Logitec products. The problem is all the ferrite and shielding around the cables that are on the desk. Apart from the looks, it limits the operating comfort. I really took a lot of necessary RFI measures. I tamed that beast so I’m a bit reluctant to change things. Each new antenna makes me cross my fingers because you never know how its radiation pattern affects the PC. Here’s a copy of a post I did two years ago. It tells how I solved my RFI issues.

The relays were clapping to the rhythm of the CW being sent. The problem was worst on 40+30m. Double six, 2 band decoders, BPF-600 filter set and reduction interface. This was a severe problem that even damaged the decoder's hardware! Tripping point was also far less than 100W, I couldn't even use the amp.
I already had a good grounding system - or at least I thought so. There were TENS of ferrite clamps everywhere too. But it didn't help.
The D6 switch is driven by the band decoder by means of two 10m long shielded (!!) cables. The shield was grounded in the shack and on the Double6 by means of the edge of the DB25 connector. That turned out not to be enough. On both ends of the control cable, I removed some of the outer insulation to expose the cable's shield and clamped a grounding strap on the shield. This strap went straight to the grounding posts in the shack and at the antenna side.
Better grounding of the control cable was the answer here and solved 90% or more of the relay "clapping" problems up to 1kW. So make sure that every DB25 has its edge connected to one of the ground pins, and that all shields are properly grounded. For  grounding wire, I use the shield of RG-213 leftovers to keep the inductance low or at least lower than a 2.5mm² wire.
Other RFI issue:
I had some problems not affecting microHAM devices but the PC. If I launched a CQ on 15m, I would lose mouse and keyboard control, which is quite painful in a contest. Or the kbd would send commands to the PC and thus the rig all by itself. On 10m exceeding 500W, WinXP was so kind as to tell me that "the computer is now shutting down". Here's how I solved it and cured the remaining 10% of the problems.

• I took the shield of RG-217 (thick) coax and routed all mouse and keyboard cables with extensions cables through this. This makes a grounded shield for the PC control cables. A Faraday cage if you will. It was not easy to get the PS/2 or USB plugs through the lengthy shield but with some fiddling and harsh words, I managed to squeeze it through.
• I bought self adhesive aluminum tape. Where PS/2 and USB extension cables get together, I taped this connection RF tight. I also used this aluminum tape to tape all connections to the PC's main board, to close all RFI holes. The backside of the keyboard too was covered with this tape, which was then used to connect this shield to the grounding wire (coax shield) slipped over the cable.
• The shielded mouse and kbd cables are then coiled up 2 to 3 times and I made a "binocular" core by means of ferrite clamp on cores. Where possible, I put ferrite clamps over all control cables. I use lots of ferrite chokes on the coax ( http://www.dx-wire.de/ ). The PC's case is also grounded to the RF ground. Most if not all of my RFI problems are now gone.

Hope this helps?
73 de Franki ON5ZO

Yesterday my copy arrived after almost two weeks. UPS can ship a complete rig in under 48 hours from W6 to ON5ZO but regular mail takes 14 days to ship a small book from the UK to here. The stamp says June 30, it arrived July 15. I’m talking about “DX Delights”, the new book by Roger G3SXW. I really enjoyed reading his other two books published by Idiom Press so I’m looking forward to reading it. I made a deal with myself I will not read it before the construction job is done.

In fact, the job itself is done. In short we removed about 90m² of concrete and paving to replace it with new stones. Every drain pipe and inspection hole underneath was changed too. Along the way we changed the shape of the terrace so there was a huge gap to be filled with ground. I’m now leveling that and hope to throw some seeds on it so it’ll turn into a lawn soon. There is other fall out too. The garage door needed adjusting, the whole garage needs repainting, all my coaxes were removed and I will have to adjust the position of the cables and the microHAM relay box. Yesterday we (XYL + me) put a big wooden pole up that will suspend the low band vertical feed point and its elevated radials. Yes, this one. I poured a concrete base that will support a huge outdoor cabinet I picked up as surplus. The plan is to put the MFJ tuner in there so it sits as close to the low band antenna as possible.

All in all there is light at the end of the tunnel here, but it’s still very faint. I hope to make some QSO in the IOTA contest to see if all still works. Probably no activity before that…

As it turns out, I finished #8 in the 2009 ARRL DX CW contest (SOAB Assisted), which is #6 EU I believe. This link tells how it went. Results will be out soon.

The closest I came to enjoying the hobby was letting the amp run idle for a few hours this morning, launch the shack PC so XP can get its dose of updates after 6 weeks and reorder the coaxes in the garage. Reorder that is, not ‘connect to relay box’…

How deep can a passionate contester sink? My last QSO was on May 31st. Currently the closest I come to the hobby is deleting tons of reflector mails every day and watch some ham related YouTube movies (like this one) during my lunch break. Even when you’re being your own boss, time is money.

No IARU. Hope to be back on the air in August…