![Overview.jpg](http://lh4.ggpht.com/_uT-6DNNXTO4/SWrKPdg4jfI/AAAAAAAARx4/-oHne2LwG1I/Overview.jpg?imgmax=800)
It's the "simplex sidebander" from Drew Diamond's "Radio projects for the amateur" first book. Dave, VK3ASE kindly gave me a couple of crystals for 3.670MHz when I visited recently. As you can guess I skipped the crystal filter and made it a double sideband exciter.
![Exciter.jpg](http://lh3.ggpht.com/_uT-6DNNXTO4/SWrLD6Up9zI/AAAAAAAARyA/yPAw4ItY4Y8/Exciter.jpg?imgmax=800)
The circuit has a 741 Op amp as a mic pre-amp, an NE612 as both the oscillator and mixer, followed by a 2N2222 buffer. That big three terminal thing is a vastly overrated 7806 voltage regulator.
Two more RF stages, comprising a 2N3053 and an IRF510 are on the second board. Finally there's the output low pass filter. I'm waiting for some more Amidon T50-2s to arrive so I can add the other filter stages.
It looks ok on the CRO (me saying "haaalow") and sounds reasonable on the local radio.
![CRO.jpg](http://lh5.ggpht.com/_uT-6DNNXTO4/SWrL6I7iO1I/AAAAAAAARyY/9fDvgoOikU8/CRO.jpg?imgmax=800)
When there's no audio, carrier is well supressed. When speaking, I get a nice 6W out by the looks.
![PowerOut.jpg](http://lh6.ggpht.com/_uT-6DNNXTO4/SWrMDXTKswI/AAAAAAAARyg/GGOf0NVuwcE/PowerOut.jpg?imgmax=800)
My construction is pretty sloppy, leads too long etc, but hey - it's 80m so pretty forgiving thankfully.
I've learned an important lesson: when a toroid is required don't just grab a random loop from the junk box, try to get something of the same material! The Amidon toroid numbers, such as FT50-2, mean FT = Ferrite, 50 is the size, 2 is the material. So, substituting an FT43-2 worked fine.
Toroids.info is a good place for specifications and winding calculators.
Update
With the help of Mike, VK2MJW, I've determined that my on-air audio is very distorted. I put this down to the RF power stages being unstable.
Interestingly the transmitter behaves quite well on a dummy load, but when connected to a real antenna tends to go into oscillation.
On it's own the exciter board sounds good. I've mounted the exciter in a nice shielded box and am currently re-building the driver and PA stages with more compact construction.
2 comments:
Looks great there Peter. Did you resolve the birdies when you put it on an antenna? I'm particularly interested because there's a Simplex sidebander on eBay right now and I'm seriously thinking of putting in a bid. My eyesight - alas - has closed the kitmaking/small scale hb tho' I can still do big things like atu's. Are you using Drew's 80M DC receiver with the simplex?
Kind regards
Norm vk5gi
Hi Norm,
Yes, I rebuilt the buffer and final stages with better, more compact construction and was successful in having a lengthy contact between Sydney and Melbourne.
At this point I'm using a commercial receiver but yes a DC receiver is under construction at the moment..
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