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Sad reality of stock vfo

Thomas Noel
 

¿ªÔÆÌåÓý

I knowingly and with full understanding of the expected consequences built out my Bitx40 fully stock. Analog VFO, original resistors etc.

All alignment went just as described in manual, and everything works just as advertised. The receiver is quite sensitive, and even without AGC it is easy to operate weak and strong stations. I have about 220kc of tuning range from 7.070 to 7.290.

The challenge is the VFO drift - even though I leave the set on all the time with volume turned down to silent, the drift is so severe that I must re-tune at least every 10-15 seconds during an attempted QSO or I drift so far off frequency that when I un-key - the other station is often gone, moved out of my passband. Never dreamed the drift would be this bad.

I have the replacement resistors for the VFO, and that will be next. I may try some of the other suggested changes just to further my own learning experience with this simple and elegant design.

But I have also ordered the DDS VFO parts!


Thomas W Noel
KF7RSF

 

quote =======

The challenge is the VFO drift - even though I leave the set on all the time with volume turned down to silent, the drift is so severe that I must re-tune at least every 10-15 seconds during an attempted QSO or I drift so far off frequency that when I un-key - the other station is often gone, moved out of my passband. Never dreamed the drift would be this bad.

unquote =====

It might be prudent to add a so called? "Huff and Puff" vfo stabiliser,
originally made and published by PA0KSB , SK?? and later simplified by Hans Summers ,G0UPL , probably on his web site.

Frank , GM0CSZ / KN6WH?????? in IO87AT
??

On Sun, Jan 1, 2017 at 3:12 AM, Thomas Noel tnoel@... [BITX20] <BITX20@...> wrote:
?

I knowingly and with full understanding of the expected consequences built out my Bitx40 fully stock. Analog VFO, original resistors etc.


All alignment went just as described in manual, and everything works just as advertised. The receiver is quite sensitive, and even without AGC it is easy to operate weak and strong stations. I have about 220kc of tuning range from 7.070 to 7.290.

The challenge is the VFO drift - even though I leave the set on all the time with volume turned down to silent, the drift is so severe that I must re-tune at least every 10-15 seconds during an attempted QSO or I drift so far off frequency that when I un-key - the other station is often gone, moved out of my passband. Never dreamed the drift would be this bad.

I have the replacement resistors for the VFO, and that will be next. I may try some of the other suggested changes just to further my own learning experience with this simple and elegant design.

But I have also ordered the DDS VFO parts!


Thomas W Noel
KF7RSF


 

In the rush to digital signal sources, it seems that we are forgetting that there are other possible
ways to correct VFO drift.
  • A few have changed the on-board chip capacitors to leaded polystyrene types and report
    good stability.

  • It is possible to build a very stable external VFO and connect this as one would do with
    a digital source.

  • Huff-and-Puff technology might be useful as a way to minimize VFO drift, whether the VFO
    is internal or external.

  • FLL (Frequency Locked Loop) technique is interesting, especially if you have built a frequency
    counter as the digital dial.? The same counter might be employed to hold to stable frequency
    settings.

Arv? K7HKL

_._



On Sat, Dec 31, 2016 at 8:12 PM, Thomas Noel tnoel@... [BITX20] <BITX20@...> wrote:
?

I knowingly and with full understanding of the expected consequences built out my Bitx40 fully stock. Analog VFO, original resistors etc.


All alignment went just as described in manual, and everything works just as advertised. The receiver is quite sensitive, and even without AGC it is easy to operate weak and strong stations. I have about 220kc of tuning range from 7.070 to 7.290.

The challenge is the VFO drift - even though I leave the set on all the time with volume turned down to silent, the drift is so severe that I must re-tune at least every 10-15 seconds during an attempted QSO or I drift so far off frequency that when I un-key - the other station is often gone, moved out of my passband. Never dreamed the drift would be this bad.

I have the replacement resistors for the VFO, and that will be next. I may try some of the other suggested changes just to further my own learning experience with this simple and elegant design.

But I have also ordered the DDS VFO parts!


Thomas W Noel
KF7RSF


 

> It might be prudent to add a so called "Huff and Puff" vfo stabiliser,
> originally made and published by PA0KSB , SK and later simplified by?
> Hans?Summers ,G0UPL , probably on his web site.

Everything you ever wanted to know about Huff & Puff stabilisers: - there you will find a library of almost every article ever written about the Huff & Puff VFO, various projects, and links to other websites with projects.

73 Hans G0UPL
 

Who has "changed the on-board chip capacitors to leaded polystyrene types and report?
good stability." With the BitX40v3, and?

which caps did you replace and with what values?

Jer aa1of
Baruch Atta
 

I have conquered the drift issue with NP0 caps in the vfo.? If you send me a sase I will send a set to you.
73
Joe w3ttt


On Dec 31, 2016 10:12 PM, "Thomas Noel tnoel@... [BITX20]" <BITX20@...> wrote:
?

I knowingly and with full understanding of the expected consequences built out my Bitx40 fully stock. Analog VFO, original resistors etc.


All alignment went just as described in manual, and everything works just as advertised. The receiver is quite sensitive, and even without AGC it is easy to operate weak and strong stations. I have about 220kc of tuning range from 7.070 to 7.290.

The challenge is the VFO drift - even though I leave the set on all the time with volume turned down to silent, the drift is so severe that I must re-tune at least every 10-15 seconds during an attempted QSO or I drift so far off frequency that when I un-key - the other station is often gone, moved out of my passband. Never dreamed the drift would be this bad.

I have the replacement resistors for the VFO, and that will be next. I may try some of the other suggested changes just to further my own learning experience with this simple and elegant design.

But I have also ordered the DDS VFO parts!


Thomas W Noel
KF7RSF


 

ohwenzelph@... [BITX20] wrote:

Who has "changed the on-board chip capacitors to leaded polystyrene types and report
good stability." With the BitX40v3, and


which caps did you replace and with what values?

Jer aa1of

?

.

I changed C91, C92 to 680pF polystyrene, C94, C95 to 47pF polypropylene, C96 to 150pF polystyrene, C95 to 82pF polystyrene, just what I had in the junk box, stability very good.

Cheers Alf vk2yac
 

quote ====
I changed C91, C92 to 680pF polystyrene, C94, C95 to 47pF polypropylene,
C96 to 150pF polystyrene, C95 to 82pF polystyrene, just what I had in
the junk box, stability very good.
unquote ====

Yes ,polystyrene caps are excellent for VFOs
I built a single FET 80 m VFO? (ugly construction)for the " UK Intermediate Licence" training , running on a 9V battery , all on an open chassis.

Once in operation for 5 minutes drift was no more than 50 Hz longer term .

Frank? ,? GM0CSZ / KN6WH??????? in IO87AT




?



On Mon, Jan 2, 2017 at 11:53 PM, Alfred fpdbase@... [BITX20] <BITX20@...> wrote:
?

ohwenzelph@... [BITX20] wrote:
>
> Who has "changed the on-board chip capacitors to leaded polystyrene
> types and report
> good stability." With the BitX40v3, and
>
>
> which caps did you replace and with what values?
>
> Jer aa1of
>
> ?
>
> .
>
>

I changed C91, C92 to 680pF polystyrene, C94, C95 to 47pF polypropylene,
C96 to 150pF polystyrene, C95 to 82pF polystyrene, just what I had in
the junk box, stability very good.

Cheers Alf vk2yac
 

thanks Alf,
so, did you end up with C95 47pF or 82pF?
jer aa1of
 

ohwenzelph@... [BITX20] wrote:

thanks Alf,

so, did you end up with C95 47pF or 82pF?
jer aa1of
Yes, C95 is 82pF, only because I did not have anymore 47pF polystyrene, also with the values I had used for C91,92 being only 680pF each, the tuning range was somewhat reduced, however I have now changed C91,92 back to 1nF, now tuning
range is from 7.007MHz to 7.268MHz, frequency stability not effected, I have 100k pot for main tuning in series with a 1k pot for fine tuning which gives 6.1kHz range. Now I can tune a conversation, go make a cuppa, come back and still be tuned to the same frequency:-)

Alf vk2yac

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