[Milsurplus] [Boatanchors] Programmable Osc Setback

[W2HX]

Dave, about the noise issue. Have you tried to see how the noise changes if you temporarily eliminate the DC-DC converted and put in a clean supply there? And what about swapping the mosfet with a bipolar with lower input impedance.  Just shooting from the hip here.

73 Eugene W2HX


-----Original Message-----
From: Boatanchors [mailto:boatanchors-bounces at mailman.qth.net] On Behalf Of David Stinson
Sent: Saturday, November 15, 2014 10:42 AM
To: milsurplus at mailman.qth.net; boatanchors at mailman.qth.net
Subject: [Boatanchors] Programmable Osc Setback

OK, you fellas can "I told ya so."   I won't complain.
On the receiver side, the tiny output of the programmable oscillators work fine and I hear no problem with increased noise floor.

Not so on the transmit side, were the osc needs considerable "boost" to drive the 6L6 grid.
My attempt to keep the TX Xtal-replacement circuit ultra-simple just isn't up to the job.  
The output is noisy and has unacceptable spurs.
Not about to give up on it- I have high hopes it can be made to work in the BC-375.

A reminder of the over-simple circuit as it is now:
http://home.netcom.com/~arc5/oscbrd.jpg
And the goal: use several of these oscillators on a satellite board to replace very expensive crystals
(aside:  Bry's crystals work well in many circuits including the RX side of this rig, but do not oscillate in this transmitter circuit).

There's a couple of ways we might go from here.
The input impedance of the MOSFET gate is quite high, so a Hi-Q tuned circuit between the OSC and Gate might bring the nastys down to something workable.
Might also turn the FET into a oscillator itself, so a tuned buffer as has been suggested might be in order.
Can you neutralize a MOSFET?
Operating the MOSFET linear might also help.

Ideas?

73 Dave AB5S

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