Saturday, February 28, 2015

PFR-3A Field Tests

Using VMEPT and a Hellschreiber WAV file I set up a beacon to transmit every two minutes with my Yeasu FT-817. Then using a half-wave piece of wire (end-fed) and a counter poise wire, I used the PFR-3A as a receiver with the internal antenna tuner to test NVIS propagation around my QTH in a 10 mile radius.

I was able to successfully decode Hellschreiber in the field using my iPhone app HERE. I also connected a small amplified speaker and recorded the audio and used that with FLDIGI to produce the screen shot above. I had hoped to use the PFR-3A to decode FSQCall but the software is centered on 1000 hz verses the 600 hz center of the PFR-3A CW crystal filter.

Saturday, February 21, 2015

Prototype Radio III - WSPR RX

Using the prototype radio from THIS post I added a simple one stage 2N2222 audio amp and after working out the frequency offset of the Si5351 clock module I was able to get successful WSPR decodes. I am driving the audio from the amp directly into the mic input of the PC and using the WSPR v2.12 software. This new version has a I-Q mode that I am taking advantage of to bring the receiver pass band up in frequency a bit. This is normally used with a SDR like a softrock but it will also work with this simple direct conversion (DC) receiver. I am currently using a Fiq in  the software of 3000hz (3Khz). This is to get the pass band out of the lower noise region  of the DC receiver (sort of a low IF). I will try higher Fiq settings later to see if there is a difference (default is 12Khz).

This is the circuit I am using. Not shown is the Si5351 clock module and the 10db 50 ohm pad used to feed the VFO input. This circuit with my simple dipole antenna and the WSPR software has achieved decodes of station from 600 to over 3000 km on 30 meters today.

This is my current Si5351 LO frequency shown below. I have not performed a calibration on my Si5351 yet which would allow the corrected frequency to be displayed (looks like it about 100hz low). This LO of 10.135.500 hz plus the 3khz I-Q mode IF of the WSPR software places me at the equivalent dial frequency of 10.138.700 hz and the WSPR tones begin 1500 hz above that with a frequency of 10.140.100 to 10.140.300 (a 200 hz wide bandwidth).
I continue to be impressed with the Si5351 clock module and this experiment validates its stability. I want to continue to work on this receiver to see how minimal I can make it. This receiver currently has no filtering to speak of outside of the antenna tuner I use to couple to my dipole. I plan to try plug-in band-pass filters and expand it in to a minimal transmitter as well.

Sunday, February 15, 2015

FSQ - Fast Simple QSO (chat) mode for HF and VHF

There is a new chat digital mode that is really slick that I have been testing. It's called FSQ for Fast Simple QSO. You can read all the details on FSQ <--HERE on ZL1BPU/ZL2AFP's web link. This mode has four speeds 6, 4.5, 3 and 2 baud. Sensitivity is believed to be about -13 dB SNR at 6 baud, and -16 dB SNR at 3 baud. That's about 10dB better and several times faster than 12 WPM Morse. The speed setting only effects the transmit speed of the app and when monitoring it will capture any for the four speeds on receive (auto-speed adjust).

The coolest feature is SELCAL. You can have it monitoring on a frequency and it will not print anything unless the message is addressed to your call sign. There are many other features with SELCAL as well including the ability to query another station to get your signal strength, their location, etc. For being a Beta version it works pretty well. I have just been testing "Acoustically Coupled" between two PC across the  room so the next step is to try it on the air. It will be interesting to see if this is usable as a QRP NVIS mode. I plan to test it on receive with a 600 Hz CW filter.

Sunday, February 8, 2015

Balloon RDF Transmitter Package

My club W6SCE is planning a balloon launch and I am providing a backup tracking solution. The solution is a Squawkbox 2 packaged in a foamcore box with a dipole antenna made from music wire and a Lithium 9 volt battery. The transmitter draws 60 mA when on so with a 600 mAh battery, thats a good 10 hours since it will be transmitting every 10 secs for 5 seconds.

The completed package weighs just 5 ounces.Here it is hanging in the operating position. The antenna is horizontally polarized which should be fine since we will be using DF antennas.

Tuesday, February 3, 2015

Prototype Radio II

I continued on the proto-board radio modules and constructed the first version of a direct conversion receiver. In the picture item #1 is the LCD I2C display, #2 is the rotary encoder, #3 is the Teensy 2.0, #4 is the SA612 mixer, and #5 is a 10 db attenuator pad for the Si5351 clock module to the right of the teensy. I drove a amplified speaker right from the output of the mixer. This does work and I copied strong CW and SSB signals.
A audio buffer amp is needed and tests will be done with SDR software next weekend.