[ARC5] Programmable Oscillators - Redux

[Peter]

I have used a DDS based on the AD9851 IC for some time. This module came 
with a LCD display and covers the frequency range from 100Khz to 50 Mhz 
in 1Hz steps.
The R-28 uses a frequency multiplication from 4 Mhz to approx. 18Mhz in 
the oscillator circuit. By removing the X-tal and feeding a 18 Mhz 
signal into the X-tal socket the Oscillator tube is used as an 
Amplifier. It worked very well.
I used an old X-tal,removed the crystal, and soldered a RG-174 cable to 
the pins as a none modification to feed the signal to X-tal socket.
  First I had some problems with the low signal from the Oscillator. I 
found an Cat TV amplifier covering 5 - 1000 Mhz with a gain of 30 dB and 
used it as a buffer between the oscillator and the R-28. Now everything 
started to work.
The receiver has an astounding sensitivity for its age.
  I use it to monitor the Tower at Centennial Airport South of Denver. ( 
118.9 Mhz )
Now I have the means to tune the R-28 to any frequency from 110 - 150 Mhz.
This oscillator was shipped from Hongkong directly to my house at no 
charge. It came with a powersupply and test cable.
Total cost $35.00 through E-bay.

Peter
KC0DGM


On 2/13/2013 7:15 PM, David Stinson wrote:
> OK hold on there a minute-  these ideas jus' keeps cooking.
>
> I turned everything off and went inside to have dinner with my sweetie 
> babies.  Then went back out and..... it didn't work.
>
> I looked at the drive from the little CMOS oscillators.
> Still at 2 P-T-P on the Osc. cathode.  Xtals give 3 Volts.  I guess 
> this just isn't quite enough to be reliable.
> So I decided to swipe the 4:1 UNUN from the TTL Osc.
> and try again.  If you remember, the CMOS oscillators won't drive the 
> UNUN primary directly- it's a DC thing- so I put another blocking cap 
> on the output.  Just happened to
> grab 680 pFd because it was laying on the bench.
> With the voltage step-up of the UNUN, the cathode is
> up to 3 V P-T-P and the receiver is back alive.
> Going to wind a 9:1 tomorrow after work and see how that does.
>
> 73 DE Dave AB5S
>
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