I just wanted to share some pictures from the bench of my progress, which is not yet fit for the ether.
I originally wanted to build a really unique design. I have a tendency to complicate things. The more simple it is, the more complicated I tend to make it. After a lot ambitious failed starts, I decided that the best thing to do is to keep it simple. In fact, I would say that I was "over-noodling" this one. So I just started building.
I build ugly circuits and I'm proud of it.
I haven't build the LPF yet and wouldn't put it on the air without one. Thanks for all the great inspiration and for inspiring a revolution of colorburst liberation!
I want to share something from Solid State Design for the Radio Amateur, W7ZOI & W1FB, page 19
"All of the circuits shown are aimed at reasonable stability, but have relatively low output power. It is possible to bias many of these circuits higher to obtain outputs of up to perhaps 1/4 watt. However, thermal stability is often severely degraded, chirp is introduced if the oscillator is keyed, and the user stands a chance of damaging the crystal from excessive rf current. It is not recommended that a single oscillator stage be used as a simple transmitter. The addition of an amplifier is so straightforward, and the system efficiency is so much better, that the minimal simplicity is not of value."That may be true, but the Mighty Mite is for learning and getting our feet wet. Still it may be interesting to point the above out or talk about it.
Also, I'm curious to know which schematics everyone is using. The famous Easy QRP transmitter on the QSL page, perhaps DeMaw's from QRP notebook (available on archive.org in pdf form for free).
73, keep your iron hot and stay fluxy,
-KE0BFF, Lawrence KS.
Without a low pass filter, this transmitter produced harmonics up to it's 12th harmonic, ~43MHz. This was determined by transmitting into a dummy load. The output was determined by using the HackRF SDR with SDRConsole v2. This was simply placed on the bench, a few feet from the transmitter. This was just a crude test. It may be possible to determine a fairly accurate estimate of the signal strength in dB (m) using this method, but at the very least it demonstrated the serious need for a LPF. The same test will be performed after an LPF added.
ReplyDeleteAlso, i recommend against using a mica compression cap. Perhaps low Q? Very little pull. a polyV may even be better. YMMV