EMRFD Message Archive 11050

Message Date From Subject
11050 2015-05-01 13:22:38 jorschei Tests with the SDR receiver


Do we really need a VFO with the high jitter crystal purity for good reception in a moderate receiver? In the files section 2 sound files recorded by PA0RWE width the 74CBTLV3253 I&Q mixer and integrated Si5351A  I2C  synthesizer. The PSoC5  Free mini is used for signal processing en demodulation. The Green mixer PCB front has only an amplitude compensation for the unwanted side band of -35 dB. There is no phase compensation yet in the PSoC5 software. The reception is not bad with the Si5351A and up to 30 MHz. Still under development......

73" PE1KTH

11051 2015-05-01 14:43:54 DuWayne Schmidlko... Re: Tests with the SDR receiver
The biggest complaint I have heard about the si5351 are its phase noise
and cross-talk between clock outputs. One thing done in many SDR
systems is to generate a clock at 4 times the desired frequency and then
divide by 4 to generate the I and Q signals. The si5351 should be good
to 160 Mhz then divided with a 74ac74 you should get up to 40 Mhz with
12db. better phase noise than generating directly at the output
frequency. With a divider for each clock you should also reduce the
cross-talk. But from the results gotten by several builders, this is
probably not necessary for the HF bands.
73 KV4QB

11054 2015-05-01 21:51:28 Ashhar Farhan Re: Tests with the SDR receiver
To each his own, it is a little like asking which is the best car? But having said that, once I drove a Porsche 911 for a few minutes. That drive enlightened me more than a semster of reading on what engineering is about. Similary, you haven't really experienced a receiver unless you have heard a direct conversion with a nice free running VFO. Fortunately, for me, for years, those receivers were the only thing I could get to work. As a result, I grew to have higher expectations from a receiver's audio than the most. 
Many in my local gang complain that I never operate any of their commercial sets. Not that I wont, but that t I can't. They are simply too noise and too complicated, they give me a headache. I tend to listen on for long hours while pottering about my work. Long hours of listening to static from a highly filtered, phase noise ridden and phase delayed sets can make you want to work for the woodpecker.  Instead, my personal preference is for 3 to 4 KHz wide receivers with low phase noise and minimal fiddling with the signal. Sure, the VFO drifts. but that is the only compromise you make. Unless you add a 10 cent huff and puff to it. 
I would recommend a five minute session on a phasing receiver for you to decide for yourself.
- f