Hello Charlie. So good to see you again. I am getting excited. With Fall and Winter approaching here in the northern hemisphere , I want to get back into the home brew. I enjoy watching your videos. Thank you.
Nice to see some more project work. I found that playing around with crystal filters that the orientation of toroids in the L-match circuits (lowpass config) affected the out of band rejection. The toroids were almost 70mm apart. Using a common relay may restrict rejection. Still worth a try
Glad to see you back! I would like to share a concern with your choice of 9 MHz IF for a 40 Meter radio. The 9 MHz may prove difficult to filter out since it is only 1.7-1.8 MHz away from the top of the 40 Meter band. The BP and LP filter filter will have to be very sharp and of a high order to ensure adequate attenuation of the 9 MHz if component. For a single band radio on 40 Meters I have used 12.288 MHz, but for 80 and 20 Meters 12.288 Mhz poses similar issues and 9 MHz would be better.
Hi Charlie you could use pin diodes to switch the RF paths and control it from the Arduino and it cheaper than relays just an idea. Looks like it should be an interesting project.
Love the video's. Want more. You get that 4PDT honker relay out of an old FT-102? I am doing the 'relay swap' in one on the bench. Love the layout. I also use a piece of plywood for projects.
I remember seeing somewhere a design for a variable bandwidth crystal filter, possibly using varicap diodes, but not sure. Not sure how much you could vary the bandwidth but thought it would be a nice idea rather than having 2 if filters .
From personal experience the CW signal from Si5351 is OK-ish. However keying a low frequency oscillator (next to the MIC on your block diagram) gives much better results and is not much more difficult to implement. I also would like to note that using Si5351 for BFO inevitably creates a lot of spurious signals. In order to build spurs-free single IF superhet receiver one have to use a well-filtered analog BFO. Naturally choosing this path will not allow you switching BFO and VFO channels. Did you consider building a rig based on amplifiers described in "A Termination Insensitive Amplifier for Bidirectional Transceivers" [PDF] by W7ZOI and K3NHI? This will also remove the loops which are not uncommon source of parasitic oscillations.
Great comments Alex and I agree with all points. I've used software keyed si5351 clocks for CW with reasonable success for some years (copying KD1JV and many others). The method is amazingly simple but you don't get to shape the keying. At QRP you can get away with it but you may not if you drive a 50w PA which will expose any roughness. I agree that a filtered crystal BFO is better than using a si5351 clock. You get a much cleaner sine wave and fewer birdies but you lose the convenience of changing the BFO frequency for USB/LSB. I've wondered about using two si5351s, one for VFO, one for BFO, but they both sit on I2C x60 so you'd have to hardware multiplex them. The symmetrical TIAs are a good idea and Wes has recently published an updated TIA schematic with AGC! Good to hear from you Alex and Charlie! 73 Paul VK3HN.
Hi Charlie, I'm getting my parts together to build my own trx. Do I need to install any libraries in to Arduino IDE which I've downloaded? If so, which ones will I need please? I like your videos, keep them coming!
There are several libraries out there you can download that will run the SI5351. AdaFruit has one. Etherkit is one I use I believe. Charlie has a video out as well on how to get it up and running.
