My levels for the mixer tests are completely unrepresentative I know; it was really to simply understand if the mixer is mixing! My LO is currently a DDS using a AD9851 and the RF is coming from a home brew analog RF signal generator (from EMIRFD).
I've just built the mic amp and I am getting about 17dB gain in that audio stage. 200mV signal in and 1.48V peak to peak out (20 log 1.48/0.2 = 17.something)
I am also seeing very good carrier suppression after the BFO and Audio mixer; 40+dB with a pair of matched 1N4148s. The attached has a 1.5KHz audio signal mixed with the BFO - the marker is on the BFO signal. You can clearly see the USB and LSB with the carrier way down.
Mark G0MGX On 19/01/2014 16:41, farhanbox@xxxxxxxxx wrote:
That's in line with my readings too. But the oscillator is 3v peak to peak! That makes it quite strong compared to the tx signal.- f Sent from BlackBerry® on Airtel ------------------------------------------------------------------------ *From: * Mark G0MGX <mark.g0mgx@xxxxxxxxx> *Sender: * minima-bounce@xxxxxxxxxxxxx *Date: *Sun, 19 Jan 2014 16:24:07 +0000 *To: *<minima@xxxxxxxxxxxxx> *ReplyTo: * minima@xxxxxxxxxxxxx *Subject: *[minima] Re: Mixers and Crystal Filters Marker 2 is the LO direct to the SA, marker 1 is post mixer. I make LO suppression through mixer is 33.4 - 8.4 = 25dB Mark G0MGX On 19/01/2014 16:00, farhanbox@xxxxxxxxx wrote:Mark, you probably swapped the z and 14 mhz values in the last sweep.Can you tell me how much local oscillator suppression are you getting? I don't know what you ref levels are.- f Sent from BlackBerry® on Airtel ------------------------------------------------------------------------ *From: * Mark G0MGX <mark.g0mgx@xxxxxxxxx> *Sender: * minima-bounce@xxxxxxxxxxxxx *Date: *Sun, 19 Jan 2014 15:15:30 +0000 *To: *<minima@xxxxxxxxxxxxx> *ReplyTo: * minima@xxxxxxxxxxxxx *Subject: *[minima] Re: Mixers and Crystal Filters All,I've added another example with a 7MHz signal to the RF port and 27MHz to the LO port and updated this page appropriately:http://g0mgx.blogspot.co.uk/2014/01/yet-more-minima.htmlI also experimented with the 15MHz low pass filter and made another using T50-6s (13 turns for 0.66u and 14 turns for 0.78u) and the sweep looks almost identical to the previous one using T50-2s so I will have to come back to that filter again as I suspect I have too much attenuation at 14MHz. We will see!I have just made the BFO and uploaded some info here: http://g0mgx.blogspot.co.uk/2014/01/minima-bfo.html Mark G0MGX On 19/01/2014 08:23, Ashhar Farhan wrote:mark,the local oscillator has to be at 27 mhz. on the higher side. this will reduce the local oscillator leakage to the RF port (you can see that the oscillator suppression isn't any great shakes. It is about -40dbm. That will be only 20 db below the tx signal level unless the LPF kicks in.- fOn Sun, Jan 19, 2014 at 1:02 PM, Mark G0MGX <mark.g0mgx@xxxxxxxxx <mailto:mark.g0mgx@xxxxxxxxx>> wrote:Hi Team Some more musings of mine on the mixer output, crystal matching and selection plus a sweep of my crystal filter... http://g0mgx.blogspot.co.uk/2014/01/yet-more-minima.html Mark G0MGX
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