Monthly Archives: August 2015

Got outside yesterday….

Temps here are still crazy hot but I braved the heat to test setting up the portable station on QRP with the magnetic loop antenna. The loop goes together really fast and I was on the air within five minutes. Made several contacts during the Indiana QSO party with good reports on 20m. Still haven’t worked anyone on  17m or 15m due to band conditions. Tear down after operating for about two hours was just as quick.


Tweaks to the Magnetic Loop Antenna

I cut some struts to support a smaller diameter coax loop on the magnetic loop antenna. This worked out great. The 6 foot coax is now tunable from 20m through 10m and uses a loop diameter of less than two feet.The 10 foot coax is tunable from 40m thru 15m and results in a loop diameter of just over three feet. The whole thing is highly portable and given my testing on 20m highly effective with up to 20W power. Here is the smaller loop:

Photo Aug 22, 2 11 47 PM

And here is the larger loop. Note how the only thing that changes are the three cross PVC pipe supports:

Photo Aug 22, 2 14 57 PM

Last modification to make is installing the capacitor and switch to use on 40m which I will do once I have completed testing the resistance losses. This was delayed as I needed to order an LM317 to use as a constant current source (Have I said lately how I miss Radio Shack?).

Upgraded my 2m Base station

I setup a new Yaesu FT-2900R 2m base station in the shack here today. The unit is built like a tank and the 75W easily lets me reach the SPI and La Feria repeaters with the existing discone antenna. Looking forward to using this on Simplex.I am interested to see if I can hear any better with this than the Baofeng. The Baofeng HT I was using as a base has returned to service as a spare HT. Hopefully I can use it to experiment with packet once I get some cables wired up. Here is what the shack is looking like now…


What’s Next for the Magnetic Loop?

I plan a series of detailed measurements for the magnetic loop antenna on 40m through 10m. First I need to build a small constant current source circuit based on a LM317 regulator. I will use this to measure the connection losses between the loop and the capacitor, as well as the losses of the cap itself. I can enter the resulting loss values into the design spreadsheet to see the effect as well as work to minimize what losses there are in the connections.Next, I will take the loop outside in the clear mounted at least one loop diameter over ground. I will tune up each band and take some SWR plots with the Mini60. This will give me a clear view of what I can expect with this antenna.

I have given some thought to a copper pipe version using 1″ copper tubing and a vacuum variable capacitor. My estimate on the cost in the $300 range. Would have to clearly beat the coax version for me to proceed…

Treating myself to Early Birthday Presents

My birthday is in a couple of weeks. With approval from the XYL  I am ordering several birthday treats that can be wrapped up before I turn the big five three. First up is a S9V33+ vertical antenna from Alpha. This is a 31 foot vertical wire antenna that can be used from 40m up to 10m and is light enough to be free standing. I will test this out first as an end fed antenna and see if I can get away with not using radials. Otherwise I will install the 4:1 balun and a set of radials and run it as a 1/4 vertical.Will be interesting to see how it does against the loop and the DXtreme. Worst case is I will have a nice light fibreglass mast.

Next on deck is a 30 foot push up mast kit from ebay. It used aluminum poles to form both a tripod and a mast.Plan to use this for additional testing of the 2m Moxon and may install as permanent mast if all goes well. Found a  low cost balun kit on ebay and ordered two. Will wire one up for 1:1 and the other for 4:1 for wire antenna experiments.

The big daddy buy was a Yaesu FT-2900R 2m mobile rig. I plan to use this as a base rig with an AC power supply. Will output 75W….so….a bit more than the 5W Baofeng I am using now. I am very interested to see how this does on the valley-wide simplex net with the 2m Moxon.

Good times even with bad propagation

A CME has been ringing the Ionosphere like a bell the last 12 hours or so. Even so, I managed 5 solid QRP contacts on 20m today with the magnetic loop indoors. Tested the loop with a shorter piece of coax and confirmed it will tune up now on 12m and 10m. No activity on those bands now though but good to know I can try them when they are open. I noticed the SWR in the loop improves with a little height. Minimum looks to be one loop diameter. Need to test the magnetic loop outside in the clear as my office had iron bars on the windows. I added the capacitor to the loop and tuned up 40m but was unable to make any contacts. I fear that the efficiency is to low or the noise floor to high or both for use on QRP. I will likely try a larger diameter loop with this and see if it improves. Performance on 20m has been solid and I am anxious to try some contacts on 17m and 15m.

I have an antenna switch on the way as I’d like to make some side by side comparisons to the end fed antenna I use on my main rig. I did use the magnetic loop on receive the other day and was picking up a station in Guatemala about 58 on the FT-817ND. I could not hear this tation on the FT-450D using the end fed wire. This station could not hear me on 5W but did when I transmitted on 100W and listened on the FT-817ND.

I made 10 solid contacts today on 40m SSB during the NA QSO party including one contact confirmed on QRZ in North Dakota. Pity this op doesn’t use LoTW…Doh!

Not a bad day of Ham Radioactivity!

Magnetic Loop Antenna Data

Portable Magnetic Loop Antenna

The link above is some details on the construction and performance of the Magnetic Loop Antenna.

Planned improvements to the Magnetic Loop antenna

I have two shorter lengths of RG-213 patch cable on order for the magnetic loop antenna.This should allow operation in the 12m and 10m bands. Will experiment between 6 ft and 5 ft loop circumference for the best match. Before drilling another hole in the case for a 40m toggle switch I decided to try just clipping the 120pF silver Mica capacitor in parallel with the variable capacitor. With this in place I was able to tune the 40m band. I did not check on the antenna analyzer but noticed that the best I could do on the Yaesu FT-817ND was three SWR bars. I was not able to make any contacts but I will keep trying. I will also run it through the antenna analyzer and see what is going on on 40m in much more detail. Next up will be thinking about how to remotely tune the antenna and trying it against the DXterme on the FT-450D. For the latter I need to get a coax switch with the idea of testing receive capabilities between the two antennas. I can transmit on the FT-450D as long as I limit power to about 15W max due to the capacitor voltage rating.

Finished some chores around the Shack

Took some time this weekend to fix a few things around the shack. First up was fixing the head of my camera tripod I use with the Buddistick and Magnetic loop antenna. A little epoxy fixed the head. Now just have to sand it a bit so the mounting pipe doesn’t fit down do tight. The magnetic loop antenna needed a reliable way to connect a wooden tuning dowel stick to the tuning capacitor. Electrical tape was what I was using and was quite crude. I took a piece of 1/2″ aluminum rod out to the mini-lathe and about 20 minutes later had a decent little shaft coupler:

Photo Aug 11, 11 07 48 AM

This little gadget really helps with the tuning and makes operating the Magnetic Loop Antenna a lot more comfortable. Essentially a 1″ piece of 1/2″ diameter aluminum rod with a 1/4″ hole bored through it. Then drilled and tapped a couple of holes for 4-40 screws.

Next up was fixing the 2m Moxon. I had not glued the PVC pieces together and even the elements were slipping out of their mounts. A bit of 5 minute epoxy fixed all of that. Thanks to Ross, W3OQ, for providing me with a PL-259 to replace the one I damaged on last use. Antenna is ready for more testing with an eye for nights with good ducting.

More Tests of the Magnetic Loop Antenna

I setup the magnetic loop antenna indoors in the shack last night and found that 20m was quite active. This time I mounted it on a speaker stand/tripod as I am still working out how to use the more portable camera tripod. One last enhancement needed is a way to couple the tuning dowel stick to the capacitor shaft. Right now I am using electrical tape which is messy and doesn’t do that great a job. Once again the antenna was connect to the FT-817ND at 5W. 20m was really wide open last night with many European and Middle Eastern stations coming in 59 but working large pile-ups. I did manage to work a station in Bosnia Herzegovina with a 59 report and another in the Czech Republic with a 57.Both contacts break the 1000 mile per watt barrier.

These reports are absolutely amazing considering the homemade antenna is indoors, about 4 feet off the ground and a with a predicted 20m efficiency of about 40%!

I am really starting to get the hang of quickly tuning the antenna to the operating frequency. First I tune for maximum noise which gets me in the ballpark. Next I key the mic at low power and fine tune the antenna for minimum SWR display on the radio. Not much of a bother except I need to be in close proximity to the antenna.

Working QRP requires a bit more patience as listening skills trump calling skills. It sometimes pays to come back around to a DX station after the “big guns” have gotten their fill. I seem to get better responses when the DX station is calling CQ or has few takers probably because my signal is not getting stepped on.

I will be taking some additional measurements on the antenna today with the Mini60 and will post the results.