Monthly Archives: September 2016

Hi-Voltage Variable Capacitor – Finished!

I wrapped the PE film around the center copper pipe lined everything else up and basically finished it! The feed mechanism works great and is not sensitive to me touching the tuning shaft. I should be able to finish the 40m loop now as the RG-213 that forms the loop will just connect to each end of the capacitor directly. I already have a toroid ready to work the matching so I will just have to size and cut the spreaders.The capacitor will be at the top of the loop this time with the feed point at the bottom. Been a great afternoon of homebrewing and realizing an idea that I had been working on for some time.


Connectors Soldered!

I did manage to solder the connectors to the ends of the copper tubes for the variable capacitor. Don’t even bother trying this with a soldering iron as there is just not enough heat.I clamped the connectors in my vise then stacked the pipe on top. A propane torch did the heating. Warm it up for about 30 seconds then start applying solder. Once it is nice and hot the solder will wick up nicely. Keep applying solder and work your way around the connector till done. Let them cool completely before handling as they are hot! The resultant joints looks mechanically solid. On to the PE film wrapping!


Homebrew Hi-voltage Variable Capacitor is Taking Shape

I mentioned in a post a while back that I successfully built a variable capacitor out of copper pipe and polyethylene sheet as a dielectric. The PE sheet has a dielectric strength of 22 kV/mm and the capacitor I have tested has a gap of almost 2.5mm! The problem that I have been working on is how to adjust this on a 40m magnetic loop antenna that I am testing for EMCOMM NVIS use. My initial tries at this either would not work mechanically or require quite a bit of structure to build. So I sat on this project awhile hoping to find a solution. I was sitting down at church last Sunday and just before the service started…BAM! the answer just popped into my head!

The secret is soldering the SO-239 connectors to the end of the pipe that form the capacitor. In this way, I not only minimize the losses but I can make the capacitor part of the mounting structure. A quick visit to Home Depot during the week yielded various PVC fittings and hardware. Here is how the prototype is looking thus far:


The PVC cylinder in the center forms part of the structure. The screw eye will be used to hoist this up onto a suitable tree branch or other support. The bottom part of this fitting will take a 1/2″ PVC pipe as a spreader which will join two together in the center. The copper pipe is the capacitor. In this test of the mechanism, I have not soldered the SO-239’s in place or have the PE sheet on the smaller tube. The block on the end of the smaller copper pipe has a couple of lock nuts sandwiching a delrin block forming a crude bearing. The other end of the threaded rod attached to a nut force fit into the PVC support. As the threaded rod is turned the smaller pipe will move in and out of the larger pipe giving me variable adjustment. The mechanism works so now I have to figure out how to solder the connectors in place, wrap the small pipe with the 45″ long piece of 4 mil PE sheet and epoxy down the parts that need to stay fixed. I have figured that for a magnetic loop that only works on the 40m band I need an adjustment range of 5pF which is about an inch of slide. The target capacitance range is 37 to 42pF. Each turn of the screw will work out to about 1/4pF so plenty sensitive to adjustment.

Stay tuned as I get out the oven mitt and the butane torch and try and do some heavy duty soldering.

Third Time Out with the 20m EFHW Antenna

Setup the 20m EFHW as a vertical on the 30ft travel mast as before. The mast is lashed to a chain link fence post and the match box is just off the ground. Checking the antenna at the feed point with the Mini60 antenna analyzer showed a bandwidth of 588 kHz with a 1.11 SWR at 14.175 MHz. The antenna is resonant across the 14.150-14.350  Mhz voice band. Then through a 50ft piece of RG-8X coax the SWR increased to 1.24 but the antenna remained resonant. Here is the station in operation:


There was a couple of QSO parties going on this afternoon so there was a rich field of domestic contacts. I operated at 45W using the FT-817ND and the amplifier.Partly cloudy day today so there were period with no direct sunshine. The following power statistics were noted:

After 1 hour Solar panel provided .644Ahr and the rig consumed .380Ahr

After 2 hours Solar panel provided 1.146Ahr and the rig consumed .904Ahr

I was unable to take a final reading as I accidentally pulled the plug on the solar panel erasing the counts. The 52W fold up panel was able to keep up with my duty cycle at full 45W.

I operated for 3 hours and made 16 QSO’s mainly in the Washington State area.No difficulties at all making the contacts and received solid 59’s across the board. Propagation during this time favored North America but Europe started opening up towards the end. I was able to copy QSO’s in progress with stations in Italy and Germany. I was not able to break the pile ups though.

All in all I am impressed with the performance of this antenna and with the ability of the solar panel to let me operate for an extended period even with periods of cloudiness. Here is a view of the antenna and the antenna fed point.


General Update

I have been pretty busy lately and have only had short periods of time where I can play radio these past few weeks.

I managed to get the 20m EFHW antenna out as a vertical again last weekend and ran on 45W for about an hour. Had some really good contacts and one short rag-chew. I trimmed the antenna a bit more and got the resonance point into the voice part of the band. This antenna is really working well.

The portable station worked well on a partly cloudy day. I used the 52W foladable panel on this outing and it just kept up with the consumption of the rig. Direct sunlight is definitely a plus.

The 60W foldable panel may have a problem. I am only getting a little over 12V in full sunlight. I will need to check the wiring as I seem to recall it was much higher before.

I setup the Raspberry PI WSPR station on my desk with a short antenna and ran it for 24 hours. My base HF receiver was able to pick up the signal and provide decodes but no other station was able to copy it. I think my next attempt will be connecting it to the Magnetic Loop on 20m. I’ll have to dig around for a suitable cable adapter but I a pretty sure I have one handy in the shack.

Most of my contacts have been using JT-65 and JT-9 on 80m, 40m, 20m, 17m and 10m. The 10m contacts I got lucky with to South America. 17m has been pretty decent to Europe in the mid-morning hours.40m is decent to Australia in the early morning just before dawn (hey, I am an early riser). Most of the activity centers around 40m and 20m.

I adjusted the programming on my DMR radio per instructions that Joe, N5JLR, provided me. No issues with this at all.

I have not worked on the HSMM gear, the 40m NVIS Loop or upgrading my window feed panel due to time. The sun continues to slow up its activity for this cycle. Getting used to working 20m and below and looking at antennas that will be me do just that.


Solar Generator Box Finished!

I finished wiring up the Solar generator box today. The wiring was straightforward but tedious. Everything is working as it should. I can open the lid of the box and monitor the PV panel and the loads with the solar charge controller and the wattmeters.So now I have 12Ahr of battery to power not just ham radio loads but also various other loads around the house all housed in a very portable ammo box. Here it is outside getting a charge from the twp 15W panels and also a view with the lid open. Overall, really pleased with the way it worked out.


Raspberry PI WSPR – Good News…Bad News

I setup the 20m Raspberry Pi with the TAPR WSPR board and tested receive on my main rig. The good news is that it sync’d up and I could decode the signals. The bad news is that the power supply I was using was “dirty”. I switched to a USB External battery and got better results but unfortunately quickly drained the battery. The other concern was that no other stations copied the signal during the time it was operating.I will clearly need to play with this some more and try a better antenna. Here is my setup with battery and board in a food container:

On more good news, The board draws about .5A @ 5V which translates to about .19A at 12V. A 12V 7Ahr battery with a 10W solar panel should let me run this day and night. I can use a 12V USB car charger to provide the 12V to 5V conversion.

20m EFHW Antenna On the Air!

It took awhile but I finally setup the EFHW antenna I has built and tuned for 20m up as a vertical outside late this afternoon. The antenna required no external tuner and I am able to run 45W into it without issue.

It worked beautifully!

This could be the best antenna I have built yet for 20m. I noticed low noise and lots of stations coming in. This on a day with SFI at 90 and SSN of 58.First contact was a soild 59 into Guatemala. Also had numerous stateside contacts all coming in nicely. One other DX into Brazil also 59. I ran the FT-817ND with solar power with the two 15W panels. Was able to put in over 1Ahr on the solar side and consumed only .66Ahr on the load side (rig and amplifier). Looks This will be my EMCOM goto system. Next step is to work on a linked antenna so that I can work other bands as needed. Here is the the whole station packed up:

Photo Sep 03, 6 43 09 PM

TAPR Raspberry Pi Shield Arrives

Here is my new 20m WSPR station, minus the antenna and 5V power supply.Equipped with 16GB SD card, Wifi USB dongle and the TAPR shield containing the filters and buffer for 20m. Power output is fixed at 20dBm.

Photo Sep 03, 4 42 17 PM