First, it is a good day when I find a new Chappy Happy project on YouTube. Thank you Chappy Happy! You make us happy!
Second, even before I watched the full video, I could recognize the PAL VFO. This is an old CB device. You will find them at hamfests. I picked one up several years ago, knowing that I will someday use it as a VFO or for VFO parts. It is, after all, an LC VFO, and it is to be celebrated and used.
Chappy Happy turns his PAL VFO into a simple direct conversion receiver for the 25 meter SW broadcast band. He is on the west coast of North America and uses it to listen to Radio Japan. He uses a J310 RF amp and an NE602 Gilbert Cell mixer.
That is great, but there is a big problem in using a direct conversion receiver to inhale AM signals: Unless you can get the frequency AND the phase of the VFO to be exactly the same as the carrier, you will have distortion. You will not have this problem if the signal is SSB, but you will have it with AM or DSB.
I think I can hear the distortion on the Radio Japan signal. Can you hear the flutter? That is what happens with an AM signal being received on a DC receiver. This is why Doug DeMaw frequently warned that you could not listen to a DSB signal on a DC receiver without significant distortion.
What do you guys think? Can you hear the distortion? Should Chappy Happy turn this receiver into a simple superhet, perhaps something like the Q-31?
Here is a video of my Q-31 super het for the 31 meter SW band:
Again, thanks Chappy Happy! Please keep those projects coming!
Nice simple straightforward and clean build! Too much QRN to tell if signal is distorted. I picked up one of those VFO's at a hamfest thinking it would be part of a future build. I am wondering how he made the new frequency dial?
ReplyDeleteI would describe the audio distortion as warbling, and since Chappy Happy apparently is interested in only one frequency he really should build the single conversion superhet receiver portion of the Knobless Wonder Transceiver by Peter Parker VK3YE and others such as Ryuu JA2NKD, whose schematic I largely used along with a 15W RF Power Amplifier to build an SSB transceiver for 3.940 MHz which is a 75M ragchew as well as an emergency communications frequency here in Central Florida where I have had at least one
ReplyDeleteQSO a week for about ten years.
The performance of both the transmit and receive functions of the
Knobless Wonder concept in my opinion are about as good as my BITX style 75M transceiver which was featured in a video on Soldersmoke of July 29, 2019.
For Chappy Happy I would suggest a homebrew 9 MHz four-crystal filter with a VXO or VFO of about 2.85 MHz, along with a higher quality speaker than what he has now.
It seems like the only active components needed for the receiver portion would be five common transistors, two diodes, and an LM386.
Note also that there was a July 19, 2024 endorsement of the Knobless Wonder design on Pete's N6QW.blogspot.com.
--Walter KA4KXX