Monthly Archives: August 2016

Planning a 20m WSPR station Using Raspberry Pi

I have a Raspberry Pi that has been sitting around the shack for years looking for an application. I have decided to implement a 20m WSPR station with it. I have ordered a 20m WSPR shield from TAPR that has the necessary LP and BP filtering needed to make it work cleanly.Expected output will be 20dBm (100mW). I will likely be using a long wire antenna with this to get started. I have also come across a 20dB amplifier development board that may come in handy if I need to run additional power. It is made by TI for their THS3202 amplifier chip.

In preparation for the board’s arrival I have been setting up the Raspberry Pi. I loaded up the operating system onto a 16GB SD card. I am running the board “headless” i.e., without a monitor, keyboard or mouse attached. A micro USB plug provides +5V power and the connection to the outside world is via an Ethernet connection. Using the application puTTY, I can open an SSH session to the Pi and interact with it. I have since installed a USB WiFi Dongle and have now eliminated the need for the wired Ethernet connection.

I would ultimately like to run this mounted outside the shack running on solar power. With this in mind I have ordered a small USB dongle that will measure the current drawn by the Pi in this circuit so I can size the panel and battery for 24 hr operation.

RASPiTwo

UPDATE: Installed the software on the Raspberry Pi with no issues today. The software is called WsprryPi and can be downloaded at GitHub through the Pi’s headless interface. Just follow the build instructions. Inital power consumption tests are showing about 400mA @ 5V.

Portable Solar Battery Pack Wiring

Here is the wiring diagram for the portable solar battery pack:

Photo Aug 30, 8 37 48 AM

The solar charge controller is a 20A unit.

Portable Solar Battery Pack

A while back, I mentioned that I had been gifted four new 12V, 6Ahr batteries. I have been working on mounting them in a large plastic ammo box along with the connections and charge controllers to use with the solar panels and the radios.Last night I drilled out the holes for the outside connections and installed braces to hold the batteries in position. Here is what it looks like thus far:

Photo Aug 30, 8 19 28 AMPhoto Aug 30, 8 20 03 AM

The front has a power switch, a Voltage meter to monitor the battery state and an output for a single pair of Anderson power poles for the load. A 12V cigarette jack is located on the side in case I want to use a small AC inverter or some other 12V load.On the side not shown is another Power Pole connection for the solar panel input and a 12V cigarette jack. The second 12V jack is direct emergency access to the batteries either as load or for mains charging. I intend to keep this on disconnected internally and will only use in an emergency. Next steps are to mount the charge controller and two watt-meters inside the box and wire the whole thing up.

 

 

Email over HF Revisited

I setup the ICOM 7100 to run with Winlink Express (formerly RMS Express) software to send email over HF. The software allows direct use of the ICOM 7100 through it’s on-board digital mode interface. Overall, this was fairly simple to setup and surprisingly I was able to send some test emails in the morning hours on 40m to a server in Houston. Be sure to select USB digital mode in the software. I set my power out to 50% and connected fairly easily. I am going to play with the settings a bit and see if I can improve connection reliability. At some point I’d like to try this using the FT-817ND as well.

Anybody who would like to exchange some test email with me can send their messages to NO5V@winlink.org

Update 4/20/2017: Per request I am attaching screenshots of my RMS Express configuration. Note that you will likely need to adjust your port settings. First up is the winmor settings:

winmor settings

Here are the Radio Settings

radio settings

Using WSPR to Compare HF Antennas

Playing with WSPR over the last few months has got me thinking about how this data can be used to compare the performance of different HF antennas. My thought is to setup two WSPR stations at the same QTH running the same band and power output over a 12 to 24 hour period. I have done this with my homebrew magnetic loop antenna and my end fed Dxtreme antenna on 40m and 20m. The data is then downloaded and reporter data is compared over time. Attached are the results as well as the raw data for this initial test.

Using WSPR to Evaluate Antennas

20m WSPR Data

40m WSPR Antenna Test Data RevA Temp

My apologies for the rough data files but I am still working on how to crunch the numbers efficiently. The methodology appears sound and opens the door to quite a bit of additional potential experimentation.

post-8766-YEAH-SCIENCE-Breaking-Bad-gif-og7N

 

Homebrew, High Voltage Variable Capacitor for Magnetic Loop Antenna

I built a prototype today of a high voltage variable capacitor for the 40m Magnetic Loop antenna I am building. My original plan was to make it a fixed capacitor out of a length of coax for a single 40m frequency. I played with cutting the coax to the right length and finally decided against this method.Instead I started looking at a “trombone” style of cylindrical capacitor made from copper pipe. After making some calculations, I settled on the following for the prototype:

  1. Inner cylinder made from 6″ of 1/2″ copper pipe: O.D. = .0.625 in
  2. Outer cylinder made from 6″ of 3/4″ copper pipe: I.D. = 0.811 in
  3. Dielectric made from 4mil Polyethylene clear plastic sheeting from Home Depot. You will need a strip about 7 inches wide and 6 feet long.
  4. A couple of sheet metal screws and some scotch tape

The nice thing about this capacitor is that PE sheet has a dielectric strength of 3kV per mil. This will easily allow operation at the 4.2kV generated in a magnetic loop when operated at 100W.

Here is what it looks like now:

 

So as a prototype definitely a success!

I have a scheme in mind to make this precision adjustable using a threaded rod so I will likely do that in the final version. On the 40m loop antenna, I expect to use this almost fully engaged and only need to tune about an 1″ of play to cover the whole band.

TYT MD-380 DMR Radio Arrives!

My TYT MD-380 arrived yesterday for DMR use. First impression is positive as looks like a solidly build radio and comes complete with charger, two UHF antennas and a USB programming cable. I downloaded the TYT software and drivers from their website and these installed without issue. I did not have the Talkgroup info available oto program this myself, but Joe, N5JLR, met with me this morning and downloaded the code block needed to setup the radio for use on the local repeater.

Amazingly crisp audio during a QSO is the result! I am looking forward to playing with this and many thanks to Joe and the local digital club for getting DMR on the air for this area.

DMR HT Radio on the Way

I ordered a TYT MD-380 DMR radio today on Amazon. It should arrive by end of next week. In preparation to setting this up, I have registered my call-sign. The local digital group has setup a local repeater that is linked to one in the upper valley as well. Should be fun to play with digital voice on UHF.

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License Test Session Yesterday

We held a license exam session yesterday and had two candidates pass. One new ham with a Technician class license and one upgrade to General. Congratulations!

Inching Closer to a QSO with the EFHW Antenna

I took out the EFHW antenna matchbox this afternoon with the intent of trimming a length of #22 gauge insulated speaker wire for 20m. I setup a little over 10m of wire with a 1m counterpoise. This was stretched out across the yard and supported by some shrubby about 4 to 5 feet off the ground. The match box was about 3 feet off the ground attached to the Mini60 antenna analyzer through a very short length of coax patch cable. The Matchbox was set at the resonance point found earlier for 20m. Initial SWR was over 3.5 at 14.1Mhz. Sweeping the frequency downwards I could clearly see the SWR improving until the reactance got to Zero and SWR was indicating just over 1:1. The wire was resonating but at a frequency much lower than I needed indicating the wire was long. I set the analyzer to 14.2Mhz and started trimming the end of the wire bit by bit until the SWR dropped to around 1.8 or so. I ran a sweep and found that the minimum SWR was right at 14Mhz while 14.35 Mhz was well above 2:1. The bandwidth was measured at 455kHz so I set the analyzer to 14.35 Mhz and trimmed until the SWR dropped to about 1.8. Here is what the SWR plot looks like finally:

2016-08-05_17-50-50

I have purposefully left it a bit long as I intend to run this as a vertical and am not sure what the effect on matching will be in its final position and with feed-line attached. I just charged up the FT-817ND and hopefully I’ll be able to take this outdoors tomorrow for a test.