Monday, January 5, 2015

30m W5OLF WSPR VCXO-AXE beacon kit (3)

When you were monitoring WSPR on 30m you probabely noticed I was on air with the WSPR VCXO-AXE. It does a excellent job. After I finished building I wanted to tune it with my frequency counter in the MFJ259B. Assuming we had to do with a USB signal I wanted to tune at the VFO frequency we normally use on our radios. But it didn't get that low. I asked AE5X John who built one a few years ago and he suggested I should try 1,65V on pin 1 of the VCXO as described in the manual. It then occured to me that the tx is probabely AM and you have to tune at the actual transmit frequency we all receive on. The tests I did proved that. At 1,65V on pin 1 the transmit frequency is 10.1402 MHz as seen on the photo from my test site.

I first connected the kit without the Gymboss timer to see if it would work. At the dummyload it gave exact 1W at 10V after I adjusted the variable cap. Just like advertised! Then I connected it at the horizontal loop and did transmission one! I monitored myself to see my signal en frequency. I noticed a lot of drift. Julian had noticed this as well and found out the problem is the heating of the 7805 voltage regulator affecting the VCXO which is nearby. Just in case I made some extra cooling with some alu foil.I later realized that the VCXO has to stabilize. And reports became better, 0 and -1 drift.

Reports from the first transmission
On the photo above you can see the oscillator signal when not transmitting and then at :26 and :30 the actual signal with drift and audio artifacts as the transmitter is very close to the receiver. I added the Gymboss timer as well now to let it run 99 cycles. I took a 8 minute time slot just like Julian did and let it run the rest of the day. For now I power it with my adjustable powersupply on 10V. But in the future I want it solar powered with a dedicated antenna. I probabely install it in the garage and not in the shack.
I was curious what the current drain would be as that is important for powering it with solar energy. I have a DC amp clamp meter which shows roughly 500mA when transmitting with 1W. A little high I think, should measure it with another multimeter. On standby it should be 34mA. At the end of the day I decided to switch it off. I was reported by 44 unique calls and best DX was VK5MR at 15690km. I ordered a 78L10 voltage regulator so I hope to connect the WSPR TX directly to a 12V supply like a solar powered battery. Not shure about the housing. And I probabely need to use a low pass filter to supress the harmonics. Anyway, that are worries for later. The WSPR TX kit works and that was one of the goals of this project.

1 comment:

Hans said...

Hallo Bas, mijn complimenten, je hebt het gefixt! De WSPR-TX werkte prima zo te zien aan de vele spots op WSPR. Helaas hebben we elkaar niet kunnen spotten en ik heb zojuist ook WSPR afgeschakeld. Leuk project, vooral als je hem straks 24 uur op zonne-energie kunt laten draaien. 73 Hans, PE1BVQ.