It all began with the nonavailability of expensive mixer ICs. I homebrewed my own mixer IC (parts shown in dotted square), and as I had already described it in my blog post of 9th February. Keen to having made the "PIXER" superhet receiver and other projects based on it...........finally I started to build a DSB rig around it but over the last couple of weeks, design evolved with a bit of tinkring here and there and ultimately it took shape of a very nice companian H.F. CW/SSB transmitter to "PIXER"; having a clean spectral purity and a a side band suppression of around 58 dB. Indeed great for a thing developed around common off the shelf components and right on your kitchen table......and all that with a home brewed X-tal filter!!! The schematic of the exciter unit is as under:
The circuit of PIXET exciter is quite simple in itself and requires no description. I have used components that were available on hand. Especially the transistors. You can substitute them with any general purpose medium power ones having adequate gain bandwidth product. Though matched pair of transistors has been used in the balanced mixer but R6 has been included for refining the circuit balance. It can be carefully adjusted for minimum carrier during no audio signal present at the microphone input. A simple diode gate provides the CW keying. Could there be anything simpler than that....? And that's the real essence of QRP home brewing.....!!!
Just wanted to let you know that I enjoy your blog very much!
ReplyDeleteGood ideas, and interesting design. Thank you, Steve-WA7JTU
Thanks for liking the blog Steve.
DeleteA questions about the project: It's a only one part article? Where are the part list and details?
ReplyDeleteThanks
They are all indicated in the schematic
DeleteNeraf, it is a two part article. The second part of the article will soon be published in my next post that contains the second mixer and RF power amplifier chain of the "PIXET" transmitter.
ReplyDeleteThanks for the time and i'll be waiting. Geetings from Canary Islands
ReplyDeleteI LIKE YOUR PROJECTS,AND IT IS VERY MUCH EDUCATIVE,I AM ABOUT TO TRY ONE MY SELF HOW CAN I GET THE PCB IN PDF FORMAT. THANKS.
ReplyDeleteVery nice projects, build by cheap parts and easy to follow.
ReplyDeleteI've ordered 10 parts of 4.43 MHz. Chrystal to have some test with the adjustable IF stage in your SW receiver. Like to know what the Loss is by using a 4 Chrystal filter?
Greetings from Holland... Hans
Like to have some test with the cascode If stage with AGC as well.
ReplyDeleteHave 15 original Philips NOS boxes (Made in Holland) with each 10 BFY 90s inside from the late 70s.
This famous transistor was used in many VHF / UHF tuner sections until the late 80s.
Like to use these for the IF cascode stage.
And somewhere in an forgotten corner i must have 2N5109s from RCA, but have to look for these parts first.
Greetings from Holland.. Hans
Nice circuit! Do you have any specs for L1 for the Gilbert cell? There's nothing on the schematic or in the article about it.
ReplyDeleteHow does your differential amplifier within the dash lines on the schematic above work with out power being applied to the collectors of Q1 and Q2?
ReplyDeleteThanks for pointing out the drafting error. L1 is centre tapped, with its centre connected to positive rail. I used 8 turns trifilar of 28SWG on T50-43.
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