Rebuilding the WARC Trap Inverted-V

Inverted V just below beam.

Fifteen years ago, I put up a trap Inverted-V antenna for 30/17m roughly the 12.5m level of the tower -- right above the rotator where the tower necks down to a single tube. A couple of years latter I added 12m traps to have  coverage of all the WARC bands. 

It was my first experiences building trap antennas. Naturally, I did everything wrong.

I originally created the traps using series-wound coax cable traps. They seemed easy enough to make, and pretty weather-proof. I also made the traps resonant in the band.

This article by Tom Rauch, W8JI showed me the error of my ways. 

Coaxial cable traps actually have a rather low Q. And any trap that is resonant in the band in use is going to induce more loss. Tom's advice is to make traps with discrete components, and put the trap resonance outside the band. 

Old coaxial Traps. The 17m traps are only 5
years old, but they are badly weathered.

From the modeling work I've done, a trap antenna works with the trap resonance just about anywhere between the two bands. I tend to push the resonant frequency close to, but just below the frequency - usually by 3-5%. They key is to make pairs of traps identical, so their resonant frequencies are  the same. 

I used a rather small value for the capacitor in the trap. The actual value isn't critical, anything will work. A smaller capacitor tends to couple less energy out past the trap above resonance. You'll always get some current in the entire antenna (unless you operate at trap resonance - but then you'll get the most trap loss, too). 

A smaller capacitor means a larger coil, and on the lower frequencies, this inductive loading shortens the antenna a bit. Pick a coil diameter so that the length / diameter ratio is somewhere between 1/2 and 1, as this generally results in higher Q. 

New traps, 17m on left, 12m on right.

The replacement traps are constructed on 1 1/2" schedule 20 PVC, which is roughly 1 5/8" OD as follows:

• 12m - 6 turns 14 gauge THHN and a 22 pF 6 kV capacitor, resonating about 24.4 MHz
• 17m - 9 turns 14 gauge THHN and a 27 pF 6 kV capacitor, resonating about 17 MHz

I used the existing length of 14 gauge THHN wire for the 12m segment, which, unfortunately, I did not measure. I'd start with 112" each side. the 17m segment is 18 1/2" of 12 gauge THHN each side, and the 30m segment is 93" 12 gauge THHN each side. The 30m segment is doubled back about 8" each side, twisted to connect to the end insulators. The total length of the antenna is about 37 feet.

I trimmed the Inverted-V by running it up the tower to about the 35 foot level using a rope and pulley. I learned this technique from the last time I repaired this antenna. This round, trimming only took four attempts. 

The antenna SWR curves fit perfectly on 30m and 12m, where the SWR is less than 1.5 and 1.2 across the entire band, respectively. 17m the SWR is closer to 2:1, with the lowest SWR at 18.010 at 1.58:1. In retrospect, perhaps I should have trimmed another 1/2" off the 17m segment. 

The apex of the Inverted-V is about 12.5 m high on the tower, about 8 feet below the A3S/A743. I used my RigExpert AA-55 to measure the SWR curves of the A3S/A743 before and after installing the WARC Inverted-V. There was no appreciable change in these curves on any band, which indicates there is little interaction between these antennas. 

4U1UN (and 4U75UN)

A little more than a year ago, I was looking at the Most Wanted list in ClubLog. I noticed that the United Nations HQ entity was number 30 on the list. In all my years of ham radio, I had never heard them on the air, much less worked them. I wondered if I'd ever have the opportunity to work them at all.

Well, the 4U1UN club has been busy, and late fall 2019, they finished their installation which allows them to remotely operate a transceiver near the top of the UN towers from a room on the ground floor of the building. Since that time, they have been sporadically active. 

I don't know what the rules are for operating 4U1UN, but the station has been active at least some time every month during the past year. They have gone from an entity you'd wonder if you'd ever work, to one that can easily be worked by anyone with a bit of determination.

Over the past year, I've kept a running DX Watch query going to see when they were on the air, and worked them any time I could hear them. They've been easy to work even with compromise antennas.

They confused me in September, as I thought they had gone silent. No, they just switched callsigns. They are celebrating 75 years of the UN with the call 4U75UN. There's a special certificate for working them. They should continue with that call until December 31st.

They'd be pretty easy from the USA on 160m, but I don't believe anyone has ever operated on that band. I doubt they have an antenna, and I head the noise level in NYC is extraordinarily high.

They QSL promptly through LoTW (be patient, it may take a week or two to be uploaded). I've gone from wondering if I'd ever work them to having them confirmed on nine bands (80m-6m) and three modes: CW, Phone and Digital. 

Keep an eye peeled on the spotting networks, and perhaps you can work a new one.

What's Next for DXCC?

At the end of summer every year, I start thinking about DXCC. For several years, it was getting more confirmations for 80m DXCC, so I could complete 5BDXCC. Last year, I accomplished that, including the 30m endorsement.

At the time of this writing, I have 109 confirmations for 17m. That band will be next - I'll submit that this year. This will also push me over the 1000 confirmations threshold for DXCC Challenge - I'll do that one at the same time.

The downside of earning DXCC awards on each band is there are fewer bands left.  On 12m, I need just 17 more confirmation. Given the low level of sunspot activity, that might take some doing. However, I did manage to add 10 confirmations since last year, so it is possible.

160m would be the next one. With 46/45 confirmations, it's further off. I'm not even half way to the necessary 100. I will definitely put some work into 160m this winter. But, honestly, DXCC on 160m may take a few years.

Speaking of years, on 6m I have a whopping seven confirmations. In the spring, I figured out how to use FT8 on this band, and while I heard a ton of DX, I only managed to work a handful. Definitely looking forward to the winter sporadic-E season. I think the most excitement I'll get for a while is finishing off 10-band confirmations. I have USA, Canada, Mexico, and Suriname on all 10 bands -- but there's several countries where I just need a 6m contact.

I've inched closer to Honor Roll, with 279/276 confirmed Mixed. have worked about nine of the remaining 64, but I need confirmations. Perhaps it is time to learn more about QSLing effectively.

And, if nothing else, it's fun building endorsements for the bands I already have. That's the fun of DXing -- it's long-term fun.

Ameritron AL-80A - Fixed!

AL-80A re-assembled, needing just 3-500Z and cover.

As I wrote previously, my AL-80A needed a repair. The plate choke was burned, with several windings melted, the protective diode and capacitor on the B- rail to ground had gone open, and I'd found that the amp would not tune on 160m -- due to some melted switch contacts.

I thought it might be a while before I could get around to doing this -- considering the last repair took about a year. However, since I had some parts on hand, I put the amplifier on the bench and got started.

1N5308 diode next to glitch
resistor on rectifier board. And
the replaced capacitor below.

First order of business was to fix the protective circuits on the B- rail. I removed the 1N4007 I had installed earlier. I tested it and found it to be completely open. Which is pretty much what I expected, given that the capacitor had opened destructively....

I replaced the capacitor with a fresh part, and installed a 1N5308 diode, as recommended by W8JI. And I mounted it on top of the board this time.

Next part to arrive was the Ameritron Plate Choke (Part Number 10-15197). It was a thing of beauty, and despite the package having a nice accordion dent in one corner, was intact.

Replacing the choke was actually pretty easy. I figured out I had to unsolder the wire to the parasitic suppressor and plate cap connector, and then the two blocking capacitors. This was much easier with the tube removed. (I put the tube inside the plate choke's packing box). I then removed the mounting screw and unsoldered the high voltage and the bypass cap.

Beautiful new choke installed.

Oh! Did I mention that you need to unplug the amplifier and make sure the plate circuit is completely discharged before sticking your hands into the amplifier? No? Gosh, that would be dumb. Of course, you do that first.

The old choke had a teflon washer under the ceramic, but it completely disintegrated when I removed the choke. I decided it wasn't required, and mounted the new choke directly to the sheet metal base.

The new choke had a slightly different geometry with respect to the lugs at the base and top. I decided to loosen the lug on the top and rotate it about 100 degrees. Otherwise, the blocking caps were not going to reach. To move the lug, I first had to unwind the top end of the winding and re-wind it to the lug. I think the choke wire ends were unsoldered for this reason.

Once in position, the lugs were easy to solder.

The final task replaces the melted switch contacts. I must say I got a lot of positive answers from the Amps email reflector (amps@contesting.com). Their diagnosis of my issues was spot on, and I got a lot of helpful advice.

Vic Rosenthal 4X6GP sent a link to an article about band-switch arcing on the Heathkit SB-1000, which essentially was a clone of the AL-80A. He suggested I should add the corona washer, which would help prevent more melted switch contacts. From what I can tell, my AL-80A is a very early model, and it did not have this modification. George Hall N2CG also sent me an email with pictures of the washer.

A huge thank you to goes to Louis Parascondolas, who not only wrote to me with suggestions on how to replace the switch contacts, but mailed me six contact elements (I needed four), plus the brass 2-56 hardware needed to secure them. Thank you, Louis!

Switch wafers disassembled. This was the hard part.
On left is the wafer where the contacts were replaced,
shown with contacts removed, and glued.

Replacing a switch contact isn't a huge deal. The first step is to remove the switch wafer. That took some doing. I deduced I could accomplish this without doing a lot of desoldering and re-wiring. The rear bandswitch wafer is basically connected to the coils and a couple of padding capacitors. One end of each coil was fastened to the capacitor studs, which simply required removing a couple of nuts. The larger coil had two small phillips screws holding it to plastic mounting blocks. The padder capacitors could also be unscrewed from their lugs. Easy right?

Not so fast! a single wire needed to be unsoldered connecting to the loading cap, and the rear switch wafer slid off with both coils attached.

The second wafer just had three connections, easily desoldered: coax and coil end, coil tap, and the cap. Once those were removed, it slid off.

The third wafer is the one we are after. I unscrewed the connection to the plate padder cap, and slid it off with the coax connection in place. That made it easier to unsolder the coax.

Once you get these wafers off, you have to handle them very gingerly! They are delicate ceramic and can easily shatter. The tricky part is to remove the old contacts. I recommend a drill press and very small drill bits to drill out the rivets holding the contacts in place. Gradually go to larger bits until you have removed all of the rivet material. Go very slowly because you don't want to break the ceramic switch wafer.

This is what I told myself, and I managed to get the contacts off with no trouble. I still had the shell of the rivet, which I carefully drilled out of the first hole. The last hole, of course, was a problem. I broke the switch wafer.

New switch contacts engaged for 160m.

I apparently said something aloud which brought my younger daughter into the basement to see if I was OK. (I was) The wafer was now in three pieces. What to do? I decided that I could glue the three pieces together, and it should hold. Superglue to the rescue! The glue took easily to the ceramic, and soon I couldn't tell where the split was.

I cleaned as much of the burnt contact debris off the two switch wafers as I could. When I was done, you could not see any discoloration of the L network (second) wafer, but there was still a little in the contact well of the 160m padder (third) wafer. The contacted would cover that up.

Adding the four contacts to the switch wafer was really easy.

Getting all the switch wafers re-assembled was the hard bit. I added the coax ground connection to the 160m padder (third) wafer, but I held off on the padder capacitor connection until the very end, so I could place the corona washer.

The L network (second) wafer was a bit problematic. I couldn't remember the orientation of the switching portion of this wafer, as there are two ways to put it on. Then I couldn't remember which wires went where. More pictures before disassembly would have been helpful. Studying the schematic made it clear which way things went.

Corona washer in place.

The bandswitch (first) wafer was easier. The tricky bit was soldering the connections to the loading capacitor.

Last bit was to install the corona washer to the padder cap. A brass washer was specified, but I didn't have one in the junk box. I made do with a steel washer and a lot of solder. I verified the continuity of the connection with an ohmmeter. Perhaps I'll redo this the next time I have to fix the amp. (which I hope may be a while)

After any fix like this, there's always the moment of truth. No sparks turning it on, and a quick test on a dummy load proved it tuned up with no surprises on 160, 80, 40, 20, 15, 10, 12, and 17m.

Ten minutes later, I had replaced all 13 cover screws and was already using the amp to chase DX on 40, 20 and 17m.

Working great again!

Uh-Oh.

There's that moment -- that moment of pure clarity. The pure clarity that occurs when you realize you've done something really stupid -- something stupid you can't take back.

This happened yesterday. You see, I got off work early and thought I'd spend the afternoon chasing a little DX. I managed to work VP6J on 12m CW, and later they moved down to 17m RTTY. I've never worked Pitcairn using RTTY, so I was watching their frequency closely. They weren't strong, but I went ahead and set up the amplifier on a clear nearby frequency. The day was waning, and I figured if they ever came up a bit so I could get clear print, I'd want to give it my best shot.

In the meantime, I moved down to 30m and worked some other stations. Of course, I switched the AL-80A to standby, and cranked up to 100 watts.

Everything was fine. Until later I went back to 17m to see how VP6J was doing. Their signal had come up a bit, and I could actually read the print well enough to try for a contact. I reached over and flipped the amplifier to operate, and clicked the button to send my call.

That's when I had my moment of clarity.

There was a loud noise from the RF compartment of the AL-80A, along with several sparks, and abruptly, it went dark. An acrid burning smell hung loosely in the air. Certainly, something had gone wrong.

I knew right away what I had done. I had transmitted 100 watts into an amplifier designed to take only 50 watts input.. An amplifier whose original design had not included 17m, and was happier with 40 watts on that band.

Roasted plate choke in AL-80A.

I switched the amp off and then back on, still dark. Clearly, I've blown a fuse. A quick check verified that one of the two 10A fuses had blown. It was replaced, and the amp came back to life. But as it turned on, there was a tiny arc coming from the plate choke. I switched it back off, turned the meter to the HV setting, and briefly switched it on again. The High Voltage looked fine, but I was going to have to get the amp on the workbench to see what was wrong with the choke.

Once I got the cover off, it was easy to see the problem. The plate choke has a black burnt mark. Looking closer, the turns of the choke had melted and separated. The choke would need to be replaced. From the location of the burn, it looks like it had arced from the end of a screw on the plate tuning capacitor to the choke.

I took the tube out and gave it a quick check with an ohmmeter. No grid to cathode or grid to plate shorts, which was good. The Taylor 3-500Z is pretty darn tough, and likely shrugged off the abuse I had just put it through.

Low voltage cap blown to protect meter.

While I had the amp on the bench, I checked out a couple of other things. Looks like one of the protective caps I placed on the B- rail to ground failed. Probably helped to protect the meter movements.

I'll be replacing that cap, along with the 1N4007 rectifier, since it must have gone open for the capacitor to fail. I'll replace it with the recommend 1N5408 rectifier, which can handle a whole lot more surge current.

Melted switch contacts.

Another mystery of this AL-80A I solved -- why it wouldn't tune up on 160m. An inspection of the front switch wafer shows that the switch contacts for the additional plate tuning cap have completely melted away. Since I've never used the amp on 160m, this was not me -- this was an existing problem. The switch contacts, or perhaps the wafer will need to be replaced to restore service on that band.

I ordered a replacement plate choke from Ameritron. They don't carry the original AL-80A part, but instead use a single choke (Part number 10-15197) for virtually all their amplifiers, including the more modern AL-80B. I've read this part avoids resonances on 17m which may be present in the original single-winding choke.

In the meantime, I'll have to chase DX without an amplifier for a while. Perhaps there won't be as many fireworks.

Update: I've been told that part of the problem with the 160m switch contacts is the lack of a corona washer. The picture clearly shows an absence of this part. I'll be adding one when I make the repair.

DXCC - Meeting the Challenge

Since I started uploading my logs to the ARRL Logbook of the World in November 2003, I've been working toward the DXCC Challenge. I've been carefully trying to work DX stations on multiple bands, hoping to get my current entity-band totals past the Challenge threshold of 1000.

Well, sometime this weekend, I received enough confirmations to get me past the 1000 mark. At the moment, I have 1003 entity-bands confirmed.

I guess I'll be submitting an application for the DXCC Challenge this year! That along with 30m DXCC.

UPDATE: I also notice that I have exactly 239 current entities confirmed for Mixed DXCC. This means I'm exactly 100 entities away from working all 339 current entities, or 91 away from the DXCC Honor Roll.

BAM! - AL-80A Broken Again

Well, crap. The AL-80A is broken again. Yup. I was on 17m chasing a bit of DX, when I decided I needed more than 100 watts. I hit the A->B button, then A/B, then tuned a bit away from the DX frequency (never tune up on DX - ever), dialed in 50 watts, switched the amp to operate and hit the Tune button.

Heard something go POP! as I turned the plate tuning knob, and immediately the grid current meter pegged. Not good.

A little diagnoses -- with no RF, keying the amplifier the grid current meter reads about 100 mA. Even with about 20 watts, the grid current meter pegs. Seeing the output meter peg, too.

At the worst, I may have fried my tube. I suspect I may have blown more of the metering circuitry.

This amplifier is very picky about 17m....

K1N - Fabulous DXpedition

My Results from K1N

Well, it's over now. The much-anticipated K1N DXpedition to Navassa Island is now over. Lucky for me, I made it into the log multiple times, which makes me quite pleased.

Granted, it was a pretty easy shot from here in northwest Georgia to Navassa Is compared to other parts of the world. They were quite strong on just about every band, with the exception of 10 and 12m. I never heard a peep from them on 6m.

The pileups in the low bands were completely crazy in the evenings. All of my contacts 30m and below were made in either the 0900z or 1000z hour -- 4 or 5 AM local. That's one of the secrets of working DX -- be on the band when others are not! The one exception was 60m, and, honestly, the channel was so crazy I'm not entirely sure how I made it into the log.

All of these contacts were made with 100 watts and wire antennas, either the Inverted-L or the 80/40m dipole. Working DX does not require huge amplifiers and large antennas.

The team on Navassa Island did a fantastic job handing out contacts despite unruly pileups, deliberate QRM and the usual craziness. I witnessed on CW pileups that extended over 30 kHz with people continuously calling. Finding the listening frequency in the second receiver was an incredibly difficult task, and quite often I was just guessing -- but a few times I got lucky.

As I told my friend Mike, W1YM, now that I have Navassa Is on nine bands, I'm planning to volunteer to operate the next time team heads to the island. Perhaps in 10 years....

Forth Quarter in Centennial QSO Party

No, I don't use paper any more....

We're now well past half-time. It's the beginning of the forth quarter.

Honestly, I'm amazed at the Centennial QSO Party. I have really enjoyed the W1AW-portable operations. I checked my records and I have made nearly 900 QSOs with W1AW-portable stations this year. 820 of those from Floyd County.

I'm kicking myself for not starting this right off the bat January 1, and pursuing these portable operations on every band/mode combination. Nope, I ignored these operations until February, and at first I was only trying to fill in bands - like 30m, 17m, and 12m - that I didn't have confirmed already.

Now, I'm having too much fun. I'm ducking into the shack each day to try and work a few band/modes that I can. It's been fantastic practice trying to break into the pileups.

I'm really, really impressed at how much I've been able to work with just 100 watts and wire antennas.

And the WARC-band WAS? I'm advancing. 30m - 45 confirmed, 17m - 40 confirmed, 12m - 29 confirmed. And there's still W1AW-portable logs that still haven't been uploaded.

If you haven't tried working these, there's still three months of fun left. Join in!

Half-time at the ARRL Centennial QSO Party

This logbook was last used in 2006.

OK, we are now half-way through the year, and that means we are half-way through the ARRL Centennial QSO Party, with portable operations of W1AW visiting all fifty states!

As I wrote earlier, the Centennial QSO Part is a great opportunity to get nine-band WAS confirmed, since all of the W1AW-portable operations are being loaded up to the Logbook of the Word (LotW).

So, it is half-time! How are we doing?

Well, I can say for one that I have been having a blast trying to work the W1AW-portable operations from Floyd county. With the dipole down, I have been forced to make all contacts with the 160/80/40m trap inverted L. The Floyd county station only has 100 watts (so does Gwinnett county as well, since I blew up the amplifier -- but that's another story).

Sometimes, I've been very successful working stations in every band and mode possible. Other times, it has been very difficult. Just recently, I worked the Alaska operation on exactly one band/mode. One. Conditions just weren't optimal for that circuit. Conditions can also be very weird. I had pretty good success with the W1AW/9 operation in Illinois, working them on all modes from 80-17m. But, I hadn't made any contacts on 15m or above. Then, yesterday morning, I worked them on 15m RTTY early in the morning. Late that the evening, at around 0200-0300z, I worked six more contacts for 15m CW, 12m SSB, and 10m SSB, CW and RTTY. Who would have thought that the band would be open on 10m two hours after sunset?

What's the secret? Well, you have to know how to bust a pileup. Other than that, it's just perseverance. Like working a Dxpedition, early in the week of operations, it is tougher to get through. By Friday or so, it is usually easier. By Sunday, they often are begging for contacts. I temper my patience by calling on Wednesday or Thursday, but I don't waste a lot of time.

And, how am I doing on the whole WARC-band WAS? If you remember, I had no states confirmed on 30m and one each on 17 and 12m when I started. Today, I have 34, 30 and 21, respectively. And there's still more logs to be uploaded from the last month of operations.

So, if you haven't jumped in to the fray, perhaps it is time. Enjoy.

How NOT to Run a W1AW/-Portable Operation

OK, I've been chasing some of the W1AW-portable operations. The light dawned on my back in February, when I realized that these operations could help me achieve WAS on the WARC bands of 30, 17 and 12m.

Managed to work quite a few, some with great ease. Some of it has to do with favorable propagation during the week they were on, but most has to do with the quality of the operators and their scheduling.

Others, I struggled to work at all, and in some cases barely made contacts on some bands. If this is the kind of operation you prefer, here's my list of tips on how to best optimize that outcome:

• Don't operate on the WARC bands. If you're not familiar with them, they are 30, 17 and 12m. These aren't terribly popular, since they have only been ham bands for a couple of decades now. I'm sure some folks don't even have equipment for these bands. Best to stick with the harmonically related bands of 40, 20, 15 and 10m, although I'm not to sure about 15m....

• Don't operate on 160 or 80m, even when it is dark. Rates will certainly be better on 40 or 20m, right. Few hams have the real estate for the enormous antennas required to operate these bands. Best to stay on the higher bands even after the sun goes down -- until the bands close, at least. 

• Don't operate exotic modes, like RTTY. Not many hams will have that fancy RTTY equipment. So, you're sure to work many more stations using good old-fashioned CW or SSB. If you must work a digital mode, make sure it is one of the new-fangled ones, like PSK 63 or JT 65.

• Don't operate split. Takes up too much bandwidth. We hams can't figure out how to set up our rigs for split anyway. Who cares if the rate really stinks, since everyone is calling on top of you. That will make getting the QSO all that much more challenging, right? 

• Don't operate between midnight and 7 AM. We hams certainly need our beauty sleep. They'll be no one to work anyway, right? Everyone should be asleep. And there's no need to start operating early in the morning, especially before sunrise. No one is awake then anyway, right?

• Don't operate more than one band at a time. Hams will get too confuse if you appear on more than one band at a time. Besides, there's probably only one band that's really open, so there's little need to move around.

OK, OK, I kid. I know, these operations are run by volunteers, and not everyone is an expert operator.  It just amazes me at how poorly scheduled a few of these operations were. It was especially frustrating wanting to work these operation on the low bands, and staying up late, or getting up early, only to find they were QRT.

I've slowly been increasing my LoTW totals for WAS from Floyd County. 

W1AW Centennial Operation - The Way To 9B WAS

OK, it took me a month to catch on. I read about the ARRL Centennial celebration. If you haven't heard about it, take a moment to check out the link. What you want to see is the Centennial QSO Party.

I'll wait.

Now, I didn't get very excited about the Centennial Points Challenge. I'm sure I'll work a few points this year just as a natural side effect of operating in contests and other events throughout the year. When I read about the W1AW portable operations from all fifty states (plus US territories), I didn't get all excited either. After all, I already have 6-band WAS. It took the LoTW and many years of work to complete that, doing mostly contest operation, so I didn't make the connection at first.

The W1AW portable operations make it easy to achieve 9-band WAS.

I think it hit me one night when I was looking at spots for FT5ZM. (Great DXpedition, if you didn't manage to work them, well, it wasn't their fault...) I saw spots for W1AW-portable. Some of them were on 30, 17 and 12m.

Now, I said I have 6-band WAS. That's because there are no contests on 30, 17 and 12m. I do operate there, but it's been mostly DXing. I do a little casual style operating with USA stations, but many of these rag chewers don't tend to QSL via LoTW.

I then made the connection -- these highly visible W1AW-portable operations are the perfect way to fill in all the holes in your LoTW WAS confirmations. All of the W1AW-portable contacts will be confirmed on LoTW. They will operate from each state twice throughout the year for an entire week, being on the air virtually all the time. Perfect.

Since then, I've been sneaking into the shack working W1AW-portable on all the bands that I need. I have two award accounts, one for Floyd County and one for the QTH in Gwinnett, so I have a chance to fill in the holes for each.

Don't have WAS? Or need WAS on a hard band like 80m, 15m or the WARC bands? This is your chance. Good luck.

WARC Trap Dipole

Although I've had good success using an untuned doublet on the WARC bands, I made up my mind that it would be nice to have an antenna that didn't require a tuner.

Initially, I built this antenna has a 30m / 17m dipole. The traps are made from 1.5" Schedule 40 PVC pipe, which is about 1.9" in diameter, wound with RG-59U coax. I built them in much the same manner as those I used later in the 80/40m dipole.

The 17m traps are 35 1/2" of coax wound as 4.8 turns. I trimmed these traps to 18.1 MHz. I actually built three traps, the first was a dummy form so I could figure out where I had to drill the holes to pull the coax down tight.

The 30/17m version uses 12 1/2 feet of wire in each leg, and the outer segments are 8 feet. You may have to trim the lengths to resonate the dipole in the band.

Adding 12m requires two more traps. These were made from 26 1/2" of coax wound in about 3 and 3/4 turns. Trimming the 12m traps right on frequency takes some doing, as small changes in length can shift the frequency of the trap considerably.

I inserted the 12m traps 9 feet 5 inches from the center, and then trimmed the length of the outer legs to bring resonance within the bands. I did not do a great job of measuring -- the 12m traps ended up in slightly different locations in each leg. It does not appear to affect the antenna much.

You should measure the antenna at some height, as the tuning will change as the antenna is raised. I did my initial trimming at 15 feet, and when raised to 42 feet, the resonance frequency rose over 200 kHz on 30m, and slightly less on 17m.

I built a current balun into the center mounting box for the dipole, using 10 type 43 1" ferrite beads, slipped over coax inside the box.

Since the WARC bands as so small, antenna SWR bandwidth isn't a consideration. At 42 feet, there's a little bit of a broadside pattern on 30, more so on 17m and 12m. Since I installed this antenna as an inverted V, the pattern is a bit more circular. The traps can easily handle the 700 or so watts on 17 and 12m.

The WARC bands are a lot of fun with a decent antenna. I've worked several DXpeditions with this dipole on 17m. Without sunspots, there hasn't been a whole lot of activity on 12m yet.

This sort of antenna is easy to build and install. There's no reason lack of antenna should keep you off the WARC bands.