how to connect DDS VFO to dx-60?

[kf6pqt]

I spent my last day of freedom ("recovery day" #2, gotta go back to work tomorrow, the GF and I went to Hawaii for a week!) building the Norcal FCC2 DDS VFO.

How to connect it to the VFO input of my DX-60? Just a coupling cap?

I googled, and I searched, but here i iz ax'ing da ques-chun.

And yes, this was my first time to KH6 land, and man, do I wanna move there!

Thanks,
Jason kf6pqt


...no, still haven't touched the DX-100 yet, hope to this weekend.

[John K5PRO]

You probably need a buffer stage, like a 2n5109 transistor, a la handbook, with a step up impedance transformer on the collector, to drive the input with some voltage. Also does the DDS stay on all the time? Might need to switch a stage on and off to prevent sidetone during receive.

[KA8WTK]

Hi Jason,
  The FCC2 is a neat little device. I built one myself but have not used it as a VFO source for a transmitter. John, I think, is correct as you would need some sort of buffer/amp/impedance circuit between the FCC2 and the DX-60. The HG-10 VFO puts out about 5 volts peak-to-peak and, if memory serves, that is into a 50k load. The FCC2 is output into a 50 ohm load.
  One other concern is the spectral purity of the FCC2. I say concern because I have not seen any data on the web about how clean it is from the usual DDS spurs.
  Just more to consider.....

Bill
KA8WTK

[John K5PRO]

You can get a 5 volt swing, with a 2N5109, maybe with 12 VDC collector Vcc. A small toroid for the output transformer will get you what you want for sure. These things are common in most of the ARRL handbook VFOs and the newer ARRL books like the excellent Experimental Methods in RF Design by Haywood, Campbell et al. I built a few on tiny piece of vectorboard, for a friend who was running a different DDS with an old Heathkit. Also used one for my DX100 for a while on the solid state VFO project which i gave up on (due to stability of VFO in that package). I have the same DDS that you have, haven't built the kit though, planned for a DX100 refurb.

73
K5PRO

[KF1Z]

  One other concern is the spectral purity of the FCC2. I say concern because I have not seen any data on the web about how clean it is from the usual DDS spurs.
  Just more to consider.....

Bill
KA8WTK

I've used mine to drive my class-e transmitter......

The spurs were 75db down from the carrier....

Not too great for high-power/quiet band conditions....
Noisy conditions you'd go unnoticed I bet.

"Legal" yes  (>45db).... 

For 100 watts output or less,,, I'd say good enough...

[K6JEK]

I use one to drive a CE 100V directly, no extra amp, no capacitor, no nothing.   

However, the 100V VFO input goes directly to a transformer which presents 35 + j11, not too far from the 50 ohms the FCC-2 would like to see.   Or maybe it's 35 -j11.  Whatever.

I'm not sure I'm going to stick with this.   I may try a little huff & puff scheme and stick with the internal VFO.

[kf6pqt]

In a fit of "try it and see" I cranked up the output on the FCC2, hooked it up to the dx-60 through a .01 uf cap, and it seems to be working FB with the 60 into a dummy load. Plenty of drive.

Am I missing something here, or does it just work? Is the dx-60 putting out a dirty signal?

I checked with a frequency counter, 3870 kc's are coming out the backside of the dx-60, just like what the screen of the vfo is saying.   Same power output as with the xtal.

[KA8WTK]

Hey, if it's working, don't mess with it!
My thoughts on adding the buffer were premised on thinking that the difference in FCC2 and HG-10 output impedance would not let the FCC2 give you enough drive. If that's not a problem, and you said it is not, then KF1Z said that in his experience the spurs are also not a problem.
There, no problems! Get it on the air!

Bill KA8WTK

[KF1Z]

Yep, if it's working....fine!

I think though I would try to step up the impedance a bit , just 'cause....
Don't forget, the FCC2 has a 600 ohm output too....

Check the output ( of the vfo) with a scope.... if things aren't right, the waveform clips and distorts.

After that..... while you're running into the dummy load.... scheck around with a receiver for spurs, and do a rough check just using the S meter...

Just look up at the 2nd, 3rd, and 5th harmonics... if those seem low enough with a local RX... you should be ok-fine.


BTW, there is already a (0.1uf, or 0.01 ?) cap at the 50 ohm output of the FCC2.

[kf6pqt]

What kind of voltage rating is that little SMT chippy-cap, though?

[KF1Z]

What kind of voltage rating is that little SMT chippy-cap, though?

Probly only 100-200 volts....

Are you connecting it to a voltage source?

(I guess there might be voltage at the  input to the rig?... I don't know nuthin' bout toob gear..)

So I suppose you're using another cap as a voltage divider or sumtin like that ?


At any rate, as we said before, if it's working that way.... fine...!

[kf6pqt]

Just the grid of the dx-60's oscillator tube, I think 6cl6.