Monthly Archives: September 2015

Accidental Magnetic Loop Antenna Stress Tests

I definitely overdid the power into the Magnetic Loop antenna when testing the new amplifier. Biggest problem was on 40m. I hit the silver mica capacitance with way more than 500V. 40m won’t tune up now as the capacitance is now reading 63pF instead of 120pF. So I have a 150pF capacitor on order than will handle 2kV to replace it.


Solar Power Capacities

I have two solar panel setups that I can use for the portable station. I have used both successfully on QRP only with the FT-817N running 5W. One setup up uses two 15W panels for a total of 30W. The other is a roll-up 60W panel. I looked up the worst case available daylight hours for this area of South Texas and found it was 4.42 hours. This works out to 7.25Ah for the 30W and 17.7Ah for the 60W panel. Two 7Ah 12V gel cell batteries provide my storage. full discharge would be at 50% of the total or 7 Ah.

In an emergency situation needing to handle traffic, I estimated needing to run 12 hours a day such that 90% is receive time (10.8 hours) and 10% (1.2 hours) is transmit time. Now using the current draw values I measured previously with the FT-817ND and the MX-P50M amplifier I have the following power needs:

QRP (5W): 7.78 Ah

20W xmit: 12.96Ah

37W xmit: 17.2Ah

From this info one can see that the QRP station will run with the 30W panels but there is no headroom in the power budget. The 60W panel has ample energy to keep the batteries topped off. This has pretty much been confirm by my portable operations as well.

With 20W and no solar charging I would have about 1/2 hours of talk time.

Power Consumption of MX-P50M Amplifier and FT-817ND

I setup a 12V, 30A power supply I have for another project to use with the MX-P50M Amplifier and the FT-817ND. I adjusted the power supply such that is has an output voltage of 13.8V. Here are the readings on 20m:

Current draw on Receive with amplifier on standby: 0.36A

Current draw on receive with amplifier on: 0.4A

Current draw with 1/2W in / 10W out : 3.69A

Current draw with 1W in / 20W out: 5.4A

Current draw with 2.5W in / 45W out: 7.2A

Current draw with 5.0W in / 60W out: 8.3A

Note that the power was measured with an SWR/wattmeter and at 5W input is clearly exceeding the 45W rating of the amplifier. So with this power supply I would limit to 20W with the magnetic loop antenna so just need to limit output power to 1W on the FT-817ND.

Next tested battery power. My portable power is provided by two 12V 7Ahr gel cell batteries connected in parallel. I hooked this up to my charge controller and measured the output voltage at 12.6V. Here are the consumption measurements:

Current draw on Receive with amplifier on standby: 0.36A

Current draw on receive with amplifier on: 0.39A

Current draw with 5W amplifier off: 1.77A

Current draw with 1W in / 20W out: 5.25

Current draw with 2.5W in / 24W out: 6.38A

Current draw with 5.0W in / 37W out: 7.0A

For 20W current draw remains the same as the power supply by my max power output is limited to 37W.

One year later…

I was granted my ham license one year ago today. Time does fly when you’re having fun!

Mini60 Analysis Software

AK4R, Steve, offers a handy Windows utility for using the MIni60 antenna analyzer with a PC. He offers it on Ebay for $5.50 (do a search for “Mini60 software”). This is a Visual Basic based utility that has some neat features if you are working with the Mini60 and a PC. Selection of amateur band specific sweeps is real easy and the step size can be varied for more detail. There is also a continuous sweep mode. I found these two features to be very useful working with the sharp SWR of the magnetic loop antenna. I can run coarse sweeps while adjusting the antenna tuning until I can see the “dip”. Then I stop continuous sweeps and do a fine sweep to measure the SWR. The program also saves the sweep data in a csv file suitable for use with Zplots and the data and graphic are stored in the system clipboard making copy and paste operations easy with Excel or Word. The install package also includes working USB/serial drivers for the mini60. Steve has also been very responsive via email supporting the software.


All in all this is a handy utility for the Mini60 and well worth a look.

2m Moxon Update

I did some tests of the 2m Moxon with the FT-2900R and an SWR/Watt meter. I wanted to check the SWR to evaluate the overall matching. I set the antenna up indoors on a tripod up about 4 feet and connected it to the radio through the meter. Starting on low power 5W at the simplex frequency of 146.52Mhz I had an SWR of 1:1. Same on 10W. At 30W I was reading an SWR of 1.5:1 and at 75W the SWR was close to 3:1. This was not unexpected behavior as the way I built the Moxon I have the feedline running through the middle of the RF field. This is not an issue with low power but at high power it puts RF on the feedline. I wound about 6 turns of coax on the feedline and the SWR dropped to about 2:1. Adding a snap on ferrite bead with three turns of coax running through it further reduced the SWR at 75W to about 1.6:1. Aside from this issue, which is easily solved with an air choke on the feedline, it looks like the 2m Moxon is ready for testing at some height and will be ready for full power from the FT-2900R.

MX-P50M Amplifier for Yaesu FT-817ND

I had been debating long and hard on a higher power rig for HF portable use. I really enjoy running the Yaesu FT-817ND on 5W QRP and portable. There are times when conditions are just plain lousy and my signal clearly doesn’t get through the noise floor. A big goal of my portable station is for running off the grid in case of an emergency. There are times when QRP will just not get through. With this in mind I have often looked at getting an FT-857D which is a mobile /portable rig capable of 100W. Unfortunately, my budget just wont allow it. I started looking at amplifiers for the FT-817ND but cost remained an issue. I ultimately came across a Chinese made 45W amplifier on Ebay that is called a MX-P50M and comes with a cable specifically for the FT-817ND. The cost for this was $189 including shipping from Hong Kong. I have read some real horror stories regarding some Chinese made amps with most being nothing more than noisy CB amps. After a bit of research I came across some favorable reports on this unit from folks like VK2QR and GM4SLV. Check out these sites for some detailed measurements. I decided to take the plunge and order one about a week ago. I just received it today and unboxed it.

The amp was well packed and came with a  DC power cable and an ACC cable but no manual. Setup with the FT-817ND is fairly straight forward. First thing was to add some Powerpole connectors to the DC supply line. I made this a “Y” connector so I can also plug in the rig’s power supply with the same cable. This cable connects to the amp to some sort of cheesy little connector which I will discuss in greater detail. The other cable connects the amp to the ACC port of the amplifier. There are two SO-239 connectors in the back, One of these goes to the antenna and the other to the radio. I connected an SWR/power meter to make some measurements and am using the magnetic loop antenna so I need to limit power to no more than 25W. The front panel has a band switch and a power/bypass switch. There are two LED’s one for power and the other to indicate transmitting. The entire unit is housed in a sturdy aluminum case with a heat-sink on the upper surface.

I hook up the coax, and the meter and the radio on a 15A 12V power supply. The amp needs only 8A at 13.8V to run at full power. I tune up the loop antenna and set the power output to 1W. I turn on the amp and….nothing….power light doesn’t light up….hmmmmm. I powered everything down again and checked the connections but still no power. On to the inline fuse holder on the amp power cable. This is a pretty weak cover and sure enough the 10A fuse inside was blown…hmmmmm. As luck would have it…no spare fuses…so off to Home Depot for a pack of 10A fuses. Insert the new fuse and power on and….nothing…check the fuse again and it was blown…aha!

Needless to say I was starting to think about how I was going to return this thing but decided to check all my connections. I unplugged the cheesy little power connector on the amp and sure enough the pins had bent. I straightened these out and made sure they made contact, replaced the blown fuse and this time…nice blue power LED light came on. Whew!

Photo Sep 21, 7 28 27 PM

From here testing proceeded nicely. I set the band switch to 20m, adjusted the Magnetic Loop antenna for min SWR with the amp off and set the power on the FT-817 to 1W. Turning the amp on gave me about 15W. 2.5W on the rig gave me around 22W which is where I intend to run it. Total Power consumption is under 5A at this power level.  Made a 20W contact on SSB into Nevada with no issues other than QSB on the band tonight. All in all I am favorably impressed with this unit. I’ll be doing some more testing with various power supply sources over the next few days. I am hoping that I can still run this on my solar power setup without excessive drain.My preliminary estimates are that with the 60W fold up solar panel used during full daylight availability in South Texas would give me 3AHr headroom  over a 12 hour period with 10% transmit time at full power.

Attended my first Exam session as a VE

I attended my first exam session today (almost a year to the day that I got my ticket) at the Sunrise Mall Food court. We had two candidates taking the exam today and both passed the Technician exam. We suggested that they try and take the General class exam and they did but did not pass. Good experience anyway for them to try out the General exam.

My 600th HF contact

XE1B became my 600th HF contact logged since becoming a ham. That was using a homemade magnetic loop antenna on 5W SSB. Tomorrow I will participate in my first license testing session as a VE. Next week I celebrate my first year of getting my Ham license. I have had a lot of fun with this hobby and look forward to many more!

Magnetic Loop Antenna Updates

I finally got around to finishing a few details on the Magnetic Loop Antenna. I installed the 120pF silver mica capacitor with a SPST toggle switch to enable use on 40m. After measuring the actual diameter of my loop I noticed it is a little larger than what calculations would expect. This is due to the added 4″ width of the capacitor enclosure as well as some variation in the length of the loop coax. As a result of this the original coax coupling loop was a bit small making it closer to 1/3 vs 1/5 loop diameters. I made a new one with the larger size and decided to build a Faraday or shielded loop vs the old one which was an unshielded loop.

The loop makes a big difference in SWR across all bands serviced by the larger diameter loop (i.e. 40m-15m). SWR is now <1.2 on all bands. The matching is much improved but I have not rationalized the effect it has on bandwidth which if I use 2:1 SWR points is much greater than what the design spreadsheet would indicate. This would mean losses are greater…except that with lower SWR, more of the SWR curve is below 2:1 making the spread larger i.e. greater bandwidth. Need to investigate this more but one reference recommends measurements using a wattmeter and a field strength meter rather than measuring VSWR.

I did build a constant current source circuit using an LM317 adjustable voltage regulator to measure the milliOhm resistance loss in the loop and the connections to the capacitor. It worked out to a total loss of 25 milliOhms. This is including the loop itself.

I plan to publish my various measurements here in the near future…meanwhile how did it all work? I tuned up 20m this afternoon and heard XE1B in Mexico City calling CQ. I answered the call on 5W with the loop indoors about four feet off the floor in a vertical position. He came right back with a 58 report!

Something is working right….