VFO instability and drift are symptoms of parts failure or implementation errors.
Sometimes its just plain broken and needs to be fixed.

If it does not have a regulated supply it will be unstable even with vacuum tubes.
If the circuit use poor quality or non temperature compensated parts they are
also trouble for drift.

I've also seen cases where just changing the oscillator tube improved matters.

HG10B with a OA2 added to stabilize the VFO volage does get better and if?
some of the caps are replaced with COG and a mix of N750 parts it will be stable.
Allowing the heat to escape doesn't hurt.? Doing this is more a matter of time
paying attention to the drift then chaning from zero temp coefficient to
-750temp coefficient until drift is near zero or going the other way. Iterate
as needed.

How stable is needed varies with application for CW or SSB less than
100hz/hour is attainable.??Getting to good enough for AM anything
under 1khz an hour will do but its easy to do much better than that.

All the same things apply to solid state VFOs.? I have built many and 1hz
an hour is not that hard with patience and maintaining a stable temperature.

Primary offenders is heat always.? Toroids like FT50-7 are about the best
at +35ppm for temperature. Varicap diodes are terrible and can easily
exceed +100PPM and also that varies with what applied votlage so
stabilizing by temperature compensation is tricky at best.? In some cases
junction transistors operated at the less an ideal operating point will heat
internally and cause drift. Most published designs are at best sloppy
and rarely was the effort made to even mention how to make it stable.

The problem with H&P is its always bouncing between two frequencies and
usually that is anywhere from 20 to 80hz.? Narrower than that and the VFO
can move out of lock to the next range up/down as the time to sample goes up.
So that required the VFO to be at least marginally stable.? Also it needs a way
to turn it off while tuning or it will fight you.

Allison?

开云体育

When time permits I will try the new code.

The result with the last version was, unintelligible TX, and with tweaks
and fussing it was "terrible audio can barely understand you"..

Allison

An AC short at the output would be less than desirable and does increase
the devices power needs and heating.

Better would be 10 to 50 ohm series and then short to ground.? Or turn
the oscillator off in software!

FYI the 5pf spec is for output rise time measurement.

Allison

Thank you all that took time to weigh in on this topic.? I have a few dds vfo's already (probably 5 including my Qrp-Labs arduino shield)? ?What I was trying to see was there a modern implementation of the h&p to use on some of the older style of vfo's.? I want to build a stable vfo without resorting to either arduino or computer control.? ?Having said that I am going to use the arduino shield as an external vfo for my Heathkit DX-60b currently under restoration.? ?I would love to use the Heathkit HG-10b external vfo but it wanders all over the band.
Anyway.? Thanks
Mike? Ve7epq?

Thanks, Alan.? At least there is some evidence that it won't self-destruct when AC-shorted!

73,
Steve VE3SMA

Hi All, I am looking for someone hopefully local or at least in the UK to repair my 80m QCX. I will pay for the repair. My QCX was delivered fully assembled ?and worked perfectly for a time but will not now transmit. I suspect that I may have transmitted when the antenna was not connected although things appeared to go ?astray ?when I changed from 12 to 15 volts psu?

Roger Taylor
G4CGU

I also wonder about how well the Si5351a would react to an AC short.

Steve,

I ran a U3S with a TX muting that simply shorted the output of the coupling capacitor to ground via a BS170. It is still working. But the consensus was that it is not a good idea.
I've no real knowledge but I do not see the loading being critical for use as a calibration tool. Maybe the 5pF is to maintain a sharp waveform. It is fed into BS170s in QRP Labs projects, much more than 5pF.

73 Alan G4ZFQ

I'm thinking about putting in a series resistor between the

I was thinking about a possibility for a feature that could be incorporated in these radios Hans has been designing.? Since the ability to interface with a GPS is already there it would be an interesting option to have a menu item that could turn on a feature which appends the latituge / longitude GPS coordinates to the beacon.? I wanted to poll the members of this list to see how many others think this would be a valuable feature and if there is enough interest perhaps Hans could add it to a future firmware release if there are enough remaining resources on the microcontroller.? I was thinking that this could allow the beacon to act as an emergency locator transmitter when configured as such.? There could be other reasons for it as well.

So the question for this poll is:? Please choose your level of interest for addind lat/long to the beacon function.

Best regards
Joe ve3vxo

The QCX-17's lpf does attenuate output on 21060 kHz a few dB...could bypass it, I reckon.

72 / 73,
Bill, N4QA

I am building a general purpose LF/MF/HF/VHF/UHF "crystal calibrator" using a Progrock and a QLG1.? But I am not sure how to deal with the RF outputs from the Progrock.? I do have them AC-coupled through 0.1 microfarad capacitors.?

The Si5351a data sheet only specifies it for a 5 pF load.? I've read in other places that 50 ohm loads result in poor crosstalk between the outputs.? But this is of little concern in the current application.? I am a bit concerned about heating....the Progrock is drawing >50mA with some combinations of output frequencies and the current does seem to depend quite a bit on the load impedance (even a few inches of open-circuited coax has a noticeable effect).? I also wonder about how well the Si5351a would react to an AC short.

I'm thinking about putting in a series resistor between the Progrock/blocking capacitor and the output of my box, or an L network of resistors, to reduce the loading on the Si5351a while providing a low impedance source (50 ohms perhaps), since there seems to be more output power than I need for this specific purpose.? At some point I may add a multiplier circuit to produce microwave harmonics - that would benefit from lots of drive, so I don't want to attenuate too much and have to amplify back up again.

Any useful thoughts on this topic?

73,
Steve VE3SMA

Thanks Bill for your reply, yes you were correct I should have fully scrutinised the manual. As my old boss used to say "if in doubt go back and read the instructions". Unforetunatley the rig no longer transmits so I am now trying to find some one locally to help me.

73 Roger G4CGU

I've been doing that successfully for years. No need for even the heat-shrink. Works wonderfully. Here's

FDIM would be even better... ;-)
--
John AE5X

Anyone know if QSX might be ready by Friedrichshafen this June 21-23?
<URL:>

eagerly watching every day,
72/73 de Ken N9VV
--
?袄冲(ツ)冲/?