[Central-Electronics] Exciting Exciter VFO Option?

Tue Dec 13 21:22:28 EST 2016

Jim,
I think you got that right, and i'm not sure how they got there with the
BC-458.  In my case with the DDS VFO it was easier.

Gent's - I'm gonna be delayed on getting the write up out.  My AD9833 DDS
crapped out, and isn't acting right.  I've ordered another from ebay as
well as trying the higher frequency AD9850.  These are on modules, and I'm
not sure what happened to my original one, but for ~$11 each from China
I'll try some others.

The DDS puts out .5v, and to get that to drive a tube rig, I built the amp
from plans I found here:
http://www.wa1ffl.com/VFO_driver_amp.pdf
I had to make a change, I couldn't get the Op amp he used from Mouser, so I
instead used the AD8055a, and it works great.  I'm not an engineer and it's
caused me to read a lot about op amps, and so I'm tweaking resistors.

The plans for this amp call for very high precision and odd value
resistors, and a couple of tantalums.  I skipped one tantalum and used an
electrolytic instead.  If I had to do it over with my new knowledge of op
amps I wouldn't have treated some of the resistor values so critcally - his
scheme makes it harder to build from the junkbox.

If you have not used an Arduino controller before, I found it fun to
experiment with.  I bought the Arduino Uno for about $35.  There's also a
book Arduino for Ham Radio which has some interesting projects.
I spent a lot of time trying to figure out how to code each component to
work, rotary encoder, 2-line display and push button switches.  All of this
code can be found online.
Difficult was finding code to handle the bounciness of the rotary encoder,
I tried writing my own, then trying several other code snippets I found
online until I found one that works.

The other thing that none of the Arduino books I have mentioned was how to
build a prototype off of the Uno board.  Google Instructable.com, and they
answer is simple.  I've ordered the chip, crystal and with a few caps I'll
try to get it to work.
I'll post more when I get the parts in, and share the code as well.
73
jeff

On Mon, Dec 12, 2016 at 7:57 PM, Jim Candela <jcandela at prodigy.net> wrote:

> Jeffrey,
>
>   I am interested in your results. Programming the offset might need some
> versatility.
>
> Let me try to remember how the scheme works with the BC-458 driving the
> 20a. The BC-458 runs something close to 5 to 5.6 Mhz. Please correct me if
> this is wrong. Also, 15m seems to confound me how they did it.
>
> 160m    (VFO X 2) - 9, ex. (5.5x2) - 9 = 2
> 80m      9 -VFO , ex. 9-5=4
> 40m      (VFO X 3) -9, ex. (5.5x3)-9= 7.5
> 20m      9 + VFO, ex. 9+5=14
> 15m      Not sure how they did this band
> 10m      With 10m option, they add a 39 Mhz oscillator & mixer to the
> BC-458. I think this used 39 -(VFO X 2), ex 39 -(5x2)= 29
>
> 73,
> Jim
> Wd5JKO
>
>
>
>
> On Monday, December 12, 2016 3:29 PM, Jeffrey Welsh <
> radioartistry at gmail.com> wrote:
>
>
> To All- just to clarify, I did build an amplifier board for the DDS.  I
> got to the point where I did some simple tests.  My main reasons For
> choosing the arduino/DDS solution are:
> - I could not find a vintage vfo that would provide the appropriate
> frequencies and I didn't want to build one based on the Arc-5s
> - I wanted a unit that would provide the correct frequency and display the
> 9 mc difference to make tuning easier
> - able to use this with other boat anchors
> -I was a programmer and couldn't ore a sufficient routine
> I'll share with the group tonight!!
> 73
>
> Sent from my iPhone
>
> On Dec 12, 2016, at 15:18, Jim Candela <jcandela at prodigy.net> wrote:
>
>
> Also realize that the 9 Mhz crystal will move a lot during the 1st hour of
> power up, and it will sometimes jump a few 100 hz on the way to being
> warmed up. My friend Hans Summers at qrp-labs.com has three kits that
> might be useful here.
>
> 1.) DDS VFO Kit, $33:  (BC458 replacement)
>
> The Si5351A VFO/Signal Generator kit has a rotary-encoder tuned output,
> and a separate independent fixed (configurable) output. Both outputs have a
> range of approximately 3.5kHz to 290MHz. A GPS receiver can be connected to
> maintain precise frequency output.
>
> 2.) Band Pass Filter Kit, $4.90:   (convert square wave from the Si5351A
> to a sine wave)
> This Band Pass Filter (BPF) kit is for receiver input filtering. It uses
> the popular double-tuned-circuit which is reliable and easy to build,
> without needing access to any special equipment. Kits are available for 10
> HF bands 160, 80, 60, 40, 30, 20, 17, 15, 12, and 10m. The kit uses a
> high-quality double-sided PCB with silk-screen, solder-mask and
> through-hole plating. The capacitors supplied with the kit are high-quality
> RF ceramics of the C0G type (a.k.a. NP0 - near-zero temperature
> coefficient). Designed for the relay-switched LPF kit
> <http://qrp-labs.com/ultimatelpf>, or your own projects!
>
> 3.) Programmable crystal oscillator, $18: (Replace 9 Mhz crystal and drive
> pentode of 6U8A as a class A voltage amplifier)
>
> This kit is a simple minimalist controller for the Si5351A Synth kit
> <http://qrp-labs.com/synth> (included with the ProgRock kit). It is
> intended as a programmable crystal replacement. It has three independent
> outputs with frequency range 3.5kHz to approx 300MHz, and can be optionally *GPS
> disciplined*.
>
> http://qrp-labs.com/
>
> Lots of ways to stabilize the beasts in a 20a, I used an VHF highband xtal
> oven and a CB crystal (ch 3 xmit?) for 9 Mhz, and a Cumbria stabilized
> X-Lock to my band hopper VFO.
>
> Jim
> Wd5JKO
>
>
>
>
>
>
> On Monday, December 12, 2016 1:21 PM, Jeffrey Welsh <
> radioartistry at gmail.com> wrote:
>
>
> I am working on the same idea, I purchased the ad9850 controlled by
> arduino, and built an amplifier with broadband toroid transformer.  It
> works, and now just need to test with the 20a.  I can send you a link of
> the amplifier schematic soon.
> 73
> Jeff kd2azi
>
> Sent from my iPhone
>
> > On Dec 12, 2016, at 14:09, Stan McIntosh <mcinsand at gmail.com> wrote:
> >
> > To all,
> >
> > Last week, the Si5351 board from Adafruit caught my eye (
> > https://learn.adafruit.com/adafruit-si5351-clock-
> generator-breakout/overview).
> > For right at $8, you get:  a board with three PLL oscillators, 8 kHz to
> 160
> > MHz, and 3Vpp for much of the output range (*IF* I understand correctly).
> > A couple are on the way to my place, and I have to wonder if this might
> be
> > good for my bench, where it would be good to have one knob control
> outputs
> > for the Drake (5.6+ MHz IF), 20A (once I get it going), and maybe a
> direct
> > oscillator.  Am I missing something?  Also, since the DDS/PLL board has a
> > low impedance output, could adjusting the voltage to match a 20A's VFO
> > input just be a matter of using a toroid step-up transformer with the
> > appropriate load resistor?
> >
> > 73
> > Stan
> > KD4BTH
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