What about the diesel engine Dodge/Mercedes/Freightliner Sprinter Van? Anyone had success using that vehicle as a mobile HF platform? I've seen a lot of them in service as FedEx delivery trucks here in the U.S.A. I understand they're quite popular in Europe. Any hams out there have experience with them?

Good point. That's why I prefer older diesel vehicles, like Mercedes sedans from the 70's and 80's. I forgot to mention that in my original post. And properly maintained, those old Mercedes diesel engines keep going and going.

Get a diesel vehicle: No spark plugs = No ignition noise

As an added benefit, you can run the engine on biodiesel. Or convert it to run on recycled veggie oil.

Reduce your carbon footprint and help keep those rare island DXCC entities above sea level!

See http://www.biodiesel.org/ for more information on biodiesel.

After experimenting with 572Bs in the AL-811 amp, I have come to the conclusion that it's best to stick with 811A tubes.

I bought a used AL-811 amplifier about 8 years ago. The seller had just replaced the original 811A tubes with a new set Chinese-made 811A's. They continued to put out full power, but after about 3 years of use, when I opened up the amp to clean out dust and check on the tube condition, I noticed those telltale welts on the plates, indicative of my having maybe taken a little too much time when tuning them up. So I decided to replace them with 572B's, not for additional power, but to give me a little more margin of error when tuning up. They worked fine, but after a few years, the power output began to drop. I examined the tubes and they looked fine physically. I then swapped the original 811A's back in and the power output came right back up to full power, even with the welts on the plates.

After lots of discussion online, I've come to the conclusion that it comes down to the relative difficulty of manufacturing 572B tubes as opposed to 811A's. The graphite plates in 572B's allow them to tolerate much higher heat dissipation than the metal plates in 811A's. However, the tendency of graphite to provide lots of nooks and crannies in which air can "hide" makes it much harder to pump out all of the air during the manufacturing process. In the "good ol' days" when tube manufacturing had higher quality control, this wasn't as much of an issue. But now, given poor quality control, a tube like the 572B, during use, will be more likely to leak air trapped in the graphite. That will eventually make the tube gassy and gradually reduce output. In the worst case, the tube will fail catastrophically, though that has not been my experience.

Sure, you'll find 811A tubes that fail prematurely, due to poor manufacturing quality control. But being easier to manufacture, at least in terms of pumping out air, there's one less point of failure. And of course, if they do fail, they're cheaper to replace.

Yes, you need to be a bit more careful when tuning up 811A's. Using an electronic keyer set to its highest speed along with a good peak reading RF wattmeter allows you to tune up at 50% duty cycle, which is much easier on the tubes than tuning up "key down" with a continuous carrier. Follow the manufacturer's instructions for tuning up your amp, or take a look at W8JI's excellent website. Properly cared for, those 811As will last a long time. And if they do fail, they're cheap to replace.

73, Martin, W7MJM

WX7G must have better eyesight than I have!    I've had good luck with the insulated #26 copper-clad Davis RF "polystealth" wire from HRO, which is similar to the Wireman product. I used it to make a full-wave 40 meter sloping delta loop, with its apex about 40 feet high, supported by a palm tree. The wire is visible, if you know where to look for it, but otherwise, I think most folks wouldn't notice it. Not quite as "invisible" as magnet wire, but it'll stay up there a lot longer and the birds won't fly into it! Indeed, the local humming birds like to rest on it. From across the street, the hummers look like they're hovering in mid air, until you notice that their wings aren't moving!

73 and good luck with your antenna plans,
Martin, W7MJM

I've had good luck with Davis RF "Poly-Stealth" 26 gauge 19 strand insulated copperweld steel wire which I bought at HRO. They sell it in 100 foot rolls. I used about 140 feet to make a full wave 40 meter delta loop. It's flexible, strong enough and doesn't stretch like copper stranded wire of similar gauge. 

Sure seems like a trap problem to me.

Water could be a problem, especially if the beam was assembled with the drain holes pointing up instead of down. You might want to check that first and, if it was incorrectly assembled, proper reassembly and a few dry days may be all that's needed to restore the beam to its original performance.

How much power do you run and on what modes? Exceeding the antenna's power rating can damage the traps in a way that might produce what you're experiencing. I believe the Mini-32a is rated for 1000 watts PEP on SSB and 500 watts PEP on CW. And if you operate any 100% duty cycle modes, like RTTY, you probably shouldn't exceed 250 watts for those modes.

Trying to operate the stock Mini-32a through a tuner on bands for which it wasn't intended, like 17 or 12 meters, could also damage the traps, even at lower power levels.

Have you tried emailing or calling Mosley? Though I never experienced the problem you've described, I've found Mosley to be very helpful when I had questions about assembly of the beam. They can certainly send you a replacement trap or traps should you determine that any are defective.

Good luck with your trouble-shooting. Hope you get your Mini-32a back to full performance soon. Let us know what you discover.

73, Martin, W7MJM

Glad you enjoyed the accordion photo, Don. I call it "my other rig." 

Don,

That should work fine, especially to the south, given the terrain you've described. I'll bet you have a great view from your QTH.

73, Martin, W7MJM

For the mast section between my Yaesu-450g rotor and my Mini-32a, I use about 2.5 feet of the thick-wall 2" OD aluminum boom material that DX Engineering sells. I use about 3.5 feet of the same aluminum boom material below the rotor, but it's secured into a 5 foot heavy-duty, stainless steel roof tripod, mounted to the roof rafters with lag bolts.

I've had no problems with this arrangement over the past year and a half, even though we sometimes get strong wind gusts during storms and occasional icing. I don't have the 12/17 meter dipole add-on, however, but I doubt that would make much of a difference.

Stainless steel or galvanized steel mast material would be stronger of course, but it would be heavier. For such a light weight beam, with such small wind surface area, 2" OD heavy-wall aluminum boom stock from DX Engineering has served well as the mast for my installation. As they say in the automobile business, however, "your mileage may vary."

I do wonder about your plan to mount your Mini-32a at only 2 feet above roof line. Mounting it in such close proximity to the roof may result in some detuning, reduced bandwidth and compromised beam pattern. My Mini-32a sits about 8 feet above my roof peak, maybe 25 feet off the ground, and seems to perform fine for me. The house sits on a hill, however; that always helps.

Good luck with your installation. See how it works and modify as necessary. Let us know your results.

73, Martin, W7MJM

If you can get a used Mosley TA-33 or TA-32 Junior in good condition for a nice price, that would be a great way to go, though it is somewhat bigger and heavier than the Mini. And yes, the Mosley website is a little bit unclear about the Mini-WARC kit. I was confused as well, but an email to Mosley and a careful review of their price sheet (the PDF you can download from their site) reveals that you can purchase the !2 and 17 meter duo-band dipole element separately and then attach it to either a Mini-32a or a Mini-33a.

Alternatively, you can buy a Mini-33a-WARC, which includes the 3-element version of the Mini plus the additional WARC dipole element, in one package and at a lower price than if you were to buy either of the Minis and then the WARC kit separately. When I purchased my Mini, I decided to just go with the Mini-32a; performance is on par with the Mini-33a, it is lighter in weight, it presents less wind-load, and is the lowest cost alternative of the Minis for tri-band coverage.

At some point, I might add the WARC dipole element, but if you know you want that element, it may be cheaper to buy the whole Mini-33a-WARC package from the get go. You can then decide whether you want to assemble it as a Mini-32a-WARC or a Mini-33a-WARC.

I've enjoyed very good results with a Mosley Mini-32a, mounted on a roof tripod, about 25 feet above ground. I rotate the antenna with a mast-mounted Yaesu 450-g. I've been using it now for more than a year.

Sure, a closer-to-full-size beam would have a bit more gain, but Mosley seems to have done a very nice job, squeezing the best performance out of a very compact design. On 10 meters, the Mini-32a is essentially a full size two-element yagi and it delivers comparable gain. Gain is a bit lower than would be delivered by a standard tri-bander on 15 and 20 meters, but not so much that you'd notice. And the front-to-back and front-to-side rejection really help on receive.

The Mini-32a is probably the lightest weight tri-band HF yagi available; that's what sold me on it. You can always attach the Mosley Mini-WARC 12 & 17 meter element to add a duo-WARC-band rotatable dipole to the array; I think the Mini-WARC element goes for about $250 new. The Mini-32a itself sells for about $400 new. Combined, that's about the price of a K4KIO 5-band Hex Beam; another way to go, if you don't mind the inverted umbrella look and heavier weight of the Hex.

Good luck with whatever you decide. Sure, if you can put up a full size beam, it will be better than a mini-beam, but the difference may not be as great as you might think. And let me tell you, the mini-beam is a big improvement over a fixed dipole at a similar height, or a near ground vertical.

73, Martin, W7MJM

Very interesting discussion, guys. In essence, an antenna system, including its supporting structure (tower, roof, whatever) has a resonant audio frequency in addition to its resonant radio frequency. Installing rope inside the aluminum elements of an antenna is a bit like adding the right amount of neutralizing capacitance to an amplifier circuit to prevent it from going into self-oscillation. 

Larry Post's < www.telepostinc.com > $200 Telepan SDR-IQ interface introduced me to the SDR world. I run it with a 20-year-old Kenwood TS-950SDX and get to experience the best of both worlds; knob tuning with the Kenwood's analog plus digital filters or click-and-go panadapter tuning of both an SDR receiver and my Kenwood. I think such "bridge" technologies will bring many older hams into exploration of what SDR has to offer.

Yes indeed Tom. This country needs to renew its commitment to education and invest in the future. No argument there.