I’ll see your Charlie Morris and raise you a Drew Diamond Extra points if you’ve had a 40m QSO with him on one of his concoctions. I’m working towards the ultimate, a Peter Parker QSO on Peter Parker Technology
I am currently building a DC receiver using a permeability tuned Franklin oscillator. I started out with the colpits oscillator that Bill Merah used in this high school DC receiver. The receiver but it is very drifty. I got the Franklin oscillator working and it appears very stable. I just need a buffer amp stage to boost the oscillator signal to a useful value. The one thing that I noticed is the sine wave output varies greatly over a relatively short frequency range. I discovered that putting an inductor in series with the gimmick capacitors helped a lot. I think the inductor I used was about a 58uH. It's what I had on hand. An adjustable choke would be ideal.
Actually there is a way to reject that interfering signal. If instead of a single mixer you use two mixers fed by LO signals 90 degrees phase shifted from each other (IQ demodulation) then you can reject the unwanted sideband. Definitely a more complicated receiver but it can be done.
Thanks Herbert. What you are describing is usually referred to as the Phasing Method. I've used this myself - only once. It formed the front end of a Phasing Software Defined Radio (The 'Really Useful Rig'). So the RF phase shift was done in hardware (with an Si5351) and then the audio phase shift was done in software (with a Teensy 3.2 MCU). Mine worked very well but it is significantly more complex than the project I'm undertaking here. Thanks for watching and commenting. 73, Nick
That's great! Welcome aboard. All the best in your study. I found the practical business of building radios helped me to understand the theoretical stuff in the course book. What to some might appear as dry facts you have to remember become tools to help you make something work. 73, Nick
I was astounded when my first homebrew 40m direct conversion receiver actually worked. By coincidence it happened on a contest weekend so I had lots of signals to listen to. But for the longest time I didn't understand why every few minutes the VFO frequency took off and then slowly returned. Finally I noticed it was when the AC kicked in and blew cool air into the room. I discovered even blowing the slightest breath on the circuit caused the frequency to immediately zoom off. So I quickly renamed my project from "a radio receiver" to "a very sensitive thermometer". I am looking forward to how you deal with this issue.
Hi there! Thanks for watching and commenting. I know exactly what you mean - I've built quite a few of those myself! I famously built one VFO that I could set at the bottom of the 80m band, go away for 5 minutes to make a cup of tea and when I returned it was at the top! The Franklin oscillator is interesting in that the sensitive frequency dependent section is somewhat buffered from the rest of the circuit. So we live in hope! 73, Nick
The RF preamp should reduce LO radiation, as well, and hopefully provide a wideband termination for the mixer/ product detector. I await the next videos with interest.
Hi Nick. Many thanks. I have just built an analog VFO based on the designs and temperature compensation presented by Frank Harris K0IYE. Fantastic! If of interest I can share more data. I would also like to try the Franklin in the near future. 73 and I look forward to following the series. 73 Dick N4HAY.
Are you sure there’s nothing that can be done about the negative and positive frequencies overlapping? Can you do a direct conversion to I/Q which would preserve the distinction between the +/- frequencies?
Hi there! Please see my response to @herbertsusmann986 below. Yes, it is possible but not without introducing a magnitude of more complexity in this project. I'm trying to keep this as simple as possible. 73, Nick
Hello Nick, Thank you for your very informative videos. I am making good progress in building Eamon Skelton's SSB transceiver. I'm at the point where I need to build a PA. Eamon has several options in the book; however, they all specify a toroid "N88AB" from Maplin. Maplin no longer sells these and I cannot find a cross reference to this toroid anywhere. Do you have any idea of what an equivalent toroid might be? Or can you recommend a more modern PA at 100 to 200 watts?
Hi Gregory, I've built a couple of 16W Skelton PAs but I used the excellent work of Glenn VK3PE who adapts Skelton's original using commonly available toroids. You can check it out (including links to his schematic) here: www.carnut.info/HF_RIG_Homebrew/HOMEBREW_HF_HAM_RIG.htm Hope this helps. Obviously the higher the power the larger the core size (and/or number of cores) you'll need to use. 73, Nick
Looking forward to this. One question Nick - where do you get the little square pcb soldering pads you use? I have been looking for them but no luck. 73s de VK6HIL
Thanks Graeme. There are several sources for the pads online. Just Google "manhattan pcb pads" and you'll find some. QRPme, Kanga and eBay all gave me some options. 73, Nick
Sir Namaste I'm from India one of the Asian country, Sir will it be possible for you to make video on Radio control circuit used in RC toys, with detail explanation , how it works , how the dc motor is controled by the Radio control circuit
Hi there! Thanks for reaching out. Unfortunately I'm not the person to ask about this. I don't have any experience with RC toys or motors I'm afraid. I'm quite sure there will be some other folks on RU-vid that will be able to help though. Happy hunting & best wishes, Nick
Thanks Trevor. Sadly I don't think mine will so tuning will be very sensitive. He was tuning AM broadcast signals as well - not 2.7KHz SSB ones like I'll be. We'll see how it goes! 73, Nick
Thanks Ace! Yes, I never thought I'd be seriously attempting to build and use an analogue VFO again. My earliest attempts several years ago did not go well! I guess you live and learn. 73, Nick
