Re: Has anyone built Ashhar's Specan?

Ashhar Farhan
 

There has been a problem, the transmit out (let's say on 14 MHz) would find it's way into the seccond mixer (the one that mixes 12 MHz up to 45 MHz). As second local oscillator was t 57 MHz. While the 12 MHz mixed to 45 MHz, the 14 MHz would mix to 57-14 = 43 MHz. 
The LC filter would pass the 43 Mhz and the 45 MHz together gladly, producing spurs at 2 MHz away (at 16 MHz and 12 MHz). The cure was to use 45 MHz crystal filters. Thankfully, they are available cheaply and easily through mouser, digikey, etc.
The second issue was that as there was no balance control between the push and the pull legs of the power chain, the even harmonics were not cancelling out. hence, i had to put additional low pass filters as well. i will update the circuit with these changes after testing it out on air for a day or two.

- f

On Tue, Jul 25, 2017 at 9:00 PM, Jerry Gaffke via Groups.Io <jgaffke@...> wrote:
Not something I would do if shipping thousands of units.  Too many people would cheat, not using the appropriate filter.  And the rig would get a bad reputation.

On Tue, Jul 25, 2017 at 08:19 am, Jerry Gaffke wrote:
 If I scratch build a uBitx, the low pass filter will probably be a lump in the coax out to the antenna.


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