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K2 BFO Test

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Tedd Wong

K2 BFO Test

I am in the process of testing the BFO on page 62. Everything tested fine up to this point but now I can not get the proper BFO range. The BFO high frequency is 4917.56 and the BFO low frequency is 4914.26. This provides a BFO range of 3.2 kHz. It appears that I can not the the BFO low frequency below 4912.7 as specified in the manual. I checked L33 to make sure R116 is not shorting any turns. Should I troubleshoot this problem before proceding? If so where else should I look. Thanks.

Ted K6OI
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Don Wilhelm-3

RE: K2 BFO Test

Ted,

Yes, you should get the BFO range and frequency correct - you can continue
with no extra effort, but it must be resolved eventually, and there is no
time like the present to do it.

Check the values of the capacitors C173 and C174, and while you are at it,
check C169 too. Additionally, check the varactors D37 and D38 for the
correct type (1SV149 - the smaller ones) qne proper orientation. Be certain
the BFO crystals were the ones you soldered in - they are typically marked
ECS D4.91 -S

If you find all the above correct, you may have to pad Capacitors C173 and
174. Should that become necessary, use 47 pf in parallel with C174 and 120
pf in parallel with C173. The padder capacitors will lower the low
frequency end more than the high frequency end of the range, so it should
work for you - but do the padding only if there is nothing else wrong with
the components.

73,
Don W3FPR

> -----Original Message-----
>
> I am in the process of testing the BFO on page 62. Everything
> tested fine up to this point but now I can not get the proper BFO
> range. The BFO high frequency is 4917.56 and the BFO low
> frequency is 4914.26. This provides a BFO range of 3.2 kHz. It
> appears that I can not the the BFO low frequency below 4912.7 as
> specified in the manual. I checked L33 to make sure R116 is not
> shorting any turns. Should I troubleshoot this problem before
> proceding? If so where else should I look. Thanks.
>
> Ted K6OI
>

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Tedd Wong

Re: RE: K2 BFO Test

In reply to this post by Tedd Wong

All the components look right. I guess I've got the dreaded high Q crystals. I've noticed in the Elecraft archives that it is possible to put a capacitor at the junction of X3/X4 to ground. Which is the preferred method?

Thanks.

>
> From: "Don Wilhelm" <[hidden email]>
> Date: 2005/12/07 Wed AM 09:30:04 PST
> To: <[hidden email]>,
> <[hidden email]>
> Subject: RE: [Elecraft] K2 BFO Test
>
> Ted,
>
> Yes, you should get the BFO range and frequency correct - you can continue
> with no extra effort, but it must be resolved eventually, and there is no
> time like the present to do it.
>
> Check the values of the capacitors C173 and C174, and while you are at it,
> check C169 too. Additionally, check the varactors D37 and D38 for the
> correct type (1SV149 - the smaller ones) qne proper orientation. Be certain
> the BFO crystals were the ones you soldered in - they are typically marked
> ECS D4.91 -S
>
> If you find all the above correct, you may have to pad Capacitors C173 and
> 174. Should that become necessary, use 47 pf in parallel with C174 and 120
> pf in parallel with C173. The padder capacitors will lower the low
> frequency end more than the high frequency end of the range, so it should
> work for you - but do the padding only if there is nothing else wrong with
> the components.
>
> 73,
> Don W3FPR
>
> > -----Original Message-----
> >
> > I am in the process of testing the BFO on page 62. Everything
> > tested fine up to this point but now I can not get the proper BFO
> > range. The BFO high frequency is 4917.56 and the BFO low
> > frequency is 4914.26. This provides a BFO range of 3.2 kHz. It
> > appears that I can not the the BFO low frequency below 4912.7 as
> > specified in the manual. I checked L33 to make sure R116 is not
> > shorting any turns. Should I troubleshoot this problem before
> > proceding? If so where else should I look. Thanks.
> >
> > Ted K6OI
> >
>

Don Wilhelm-3

RE: RE: K2 BFO Test

The preferred method of padding the BFO capacitors is to maintain the ratio
between C173 and C174 by paralleling them with capacitors. A single
capacitor from the junction to ground will be in parallel with the series
combination of C173 and the varactor D38 and could make the BFO less stable
than it should be.

You are welcome to try the single capacitor solution, but do beware of the
pitfalls. If you would like further documentation on padding the BFO,
download the K2 AtoB instructions and look at the 2nd column of page 12.

73,
Don W3FPR

> -----Original Message-----
>
> All the components look right. I guess I've got the dreaded high
> Q crystals. I've noticed in the Elecraft archives that it is
> possible to put a capacitor at the junction of X3/X4 to ground.
> Which is the preferred method?
>
> Thanks.
> >
> > From: "Don Wilhelm" <[hidden email]>
> > Date: 2005/12/07 Wed AM 09:30:04 PST
> > To: <[hidden email]>,
> > <[hidden email]>
> > Subject: RE: [Elecraft] K2 BFO Test
> >
> > Ted,
> >
> > Yes, you should get the BFO range and frequency correct - you
> can continue
> > with no extra effort, but it must be resolved eventually, and
> there is no
> > time like the present to do it.
> >
> > Check the values of the capacitors C173 and C174, and while you
> are at it,
> > check C169 too. Additionally, check the varactors D37 and D38 for the
> > correct type (1SV149 - the smaller ones) qne proper
> orientation. Be certain
> > the BFO crystals were the ones you soldered in - they are
> typically marked
> > ECS D4.91 -S
> >
> > If you find all the above correct, you may have to pad
> Capacitors C173 and
> > 174. Should that become necessary, use 47 pf in parallel with
> C174 and 120
> > pf in parallel with C173. The padder capacitors will lower the low
> > frequency end more than the high frequency end of the range, so
> it should
> > work for you - but do the padding only if there is nothing else
> wrong with
> > the components.
> >
> > 73,
> > Don W3FPR
> >

Tedd Wong

RE: RE: K2 BFO Test

In reply to this post by Tedd Wong

I just added the pad capacitors to c174 and c173. It helped but not enough. The high freq. is now 4917.37 and low is 4913.92 for a range of 3.45 kHz. Is it possible to get new crystals from Elecraft if indeed I do have the ones with the higher Q?

Thanks

>
> From: "Don Wilhelm" <[hidden email]>
> Date: 2005/12/07 Wed PM 01:31:31 PST
> To: <[hidden email]>, <[hidden email]>
> Subject: RE: RE: [Elecraft] K2 BFO Test
>
> The preferred method of padding the BFO capacitors is to maintain the ratio
> between C173 and C174 by paralleling them with capacitors. A single
> capacitor from the junction to ground will be in parallel with the series
> combination of C173 and the varactor D38 and could make the BFO less stable
> than it should be.
>
> You are welcome to try the single capacitor solution, but do beware of the
> pitfalls. If you would like further documentation on padding the BFO,
> download the K2 AtoB instructions and look at the 2nd column of page 12.
>
> 73,
> Don W3FPR
>
> > -----Original Message-----
> >
> > All the components look right. I guess I've got the dreaded high
> > Q crystals. I've noticed in the Elecraft archives that it is
> > possible to put a capacitor at the junction of X3/X4 to ground.
> > Which is the preferred method?
> >
> > Thanks.
> > >
> > > From: "Don Wilhelm" <[hidden email]>
> > > Date: 2005/12/07 Wed AM 09:30:04 PST
> > > To: <[hidden email]>,
> > > <[hidden email]>
> > > Subject: RE: [Elecraft] K2 BFO Test
> > >
> > > Ted,
> > >
> > > Yes, you should get the BFO range and frequency correct - you
> > can continue
> > > with no extra effort, but it must be resolved eventually, and
> > there is no
> > > time like the present to do it.
> > >
> > > Check the values of the capacitors C173 and C174, and while you
> > are at it,
> > > check C169 too. Additionally, check the varactors D37 and D38 for the
> > > correct type (1SV149 - the smaller ones) qne proper
> > orientation. Be certain
> > > the BFO crystals were the ones you soldered in - they are
> > typically marked
> > > ECS D4.91 -S
> > >
> > > If you find all the above correct, you may have to pad
> > Capacitors C173 and
> > > 174. Should that become necessary, use 47 pf in parallel with
> > C174 and 120
> > > pf in parallel with C173. The padder capacitors will lower the low
> > > frequency end more than the high frequency end of the range, so
> > it should
> > > work for you - but do the padding only if there is nothing else
> > wrong with
> > > the components.
> > >
> > > 73,
> > > Don W3FPR
> > >
>
>

Sverre Holm-2

RE: RE: K2 BFO Test

In reply to this post by Don Wilhelm-3

> -----Original Message-----
>
> The preferred method of padding the BFO capacitors is to
> maintain the ratio between C173 and C174 by paralleling them
> with capacitors. A single capacitor from the junction to
> ground will be in parallel with the series combination of
> C173 and the varactor D38 and could make the BFO less stable
> than it should be.
>

Don,

How about a single capacitor (1-4 pF) from the junction of the crystals and
the L33 inductor as in
http://www.ac6rm.net/mailarchive/html/elecraft-list/2005-08/msg00562.html?
Does that create potential stability problems also?

I've got this link on my K2 mods page and just wanted to make sure I can
recommend it and keep it there. I have never had any problems with BFO range
myself so I have no personal experience with this myself.

73

Sverre
LA3ZA
http://www.qslnet.de/la3za/

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Ken Wagner K3IU

RE: RE: K2 BFO Test

Sverre:

This fix (that you describe) worked for me on a K2 that I built within the
past year. The LOW BFO freq was just slightly high and putting a low value
cap as you describe lowered the LOW freq to within specs, didn't change the
high BFO freq, and did not cause any instability. I don't remember the exact
value cap I used and the K2 is no longer here for me to look at.

73,
Ken K3IU

-----Original Message-----
From: [hidden email]
[mailto:[hidden email]] On Behalf Of Sverre Holm
Sent: Thursday, December 08, 2005 4:07 PM
To: [hidden email]; [hidden email]
Subject: RE: RE: [Elecraft] K2 BFO Test

> -----Original Message-----
>
> The preferred method of padding the BFO capacitors is to maintain the
> ratio between C173 and C174 by paralleling them with capacitors. A
> single capacitor from the junction to ground will be in parallel with
> the series combination of
> C173 and the varactor D38 and could make the BFO less stable than it
> should be.
>

Don,

How about a single capacitor (1-4 pF) from the junction of the crystals and
the L33 inductor as in
http://www.ac6rm.net/mailarchive/html/elecraft-list/2005-08/msg00562.html?
Does that create potential stability problems also?

I've got this link on my K2 mods page and just wanted to make sure I can
recommend it and keep it there. I have never had any problems with BFO range
myself so I have no personal experience with this myself.

73

Sverre
LA3ZA
http://www.qslnet.de/la3za/

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Don Wilhelm-3

RE: RE: K2 BFO Test

In reply to this post by Sverre Holm-2

Sverre,

I have not tried that small capacitor from the junction of the crystals and
L33 so I cannot comment on it from that standpoint.

What I would like to state is that when one pulls a crystal by any method,
the stability becomes worse as the amount of pulling becomes greater. One
should be aware of this and related facts when modifying any circuit in a
way that is not 'approved and tested'. Also due to the nature of crystals,
something that happens to work in one situation may not work the same for
all cases. Remember that I am only bringing up cautions here, I am not
makeing a firm statement about the operation one way or another.

It certainly would be nice if someone (or better yet, several someones) with
access to suitable instrumentation could try this or any other mod and
report the results. The fact that it worked on a sample of one does not
create a statement that it will work in other cases - that is simple
statistical knowledge - I would like to see something that says it works in
at least 5 or 10 trials before drawing any firm conclusions.

So, yes I think it should be left on your website, but you may want to put a
"Use at your own peril" disclaimer on all those that are not 'approved by
Elecraft' or otherwise adequately tested (and I invite you to add any of my
mods to that group as well, even though I have absolute confidence in my own
work).

73,
Don W3FPR

> -----Original Message-----
> >
> > The preferred method of padding the BFO capacitors is to
> > maintain the ratio between C173 and C174 by paralleling them
> > with capacitors. A single capacitor from the junction to
> > ground will be in parallel with the series combination of
> > C173 and the varactor D38 and could make the BFO less stable
> > than it should be.
> >
>
> Don,
>
> How about a single capacitor (1-4 pF) from the junction of the
> crystals and
> the L33 inductor as in
> http://www.ac6rm.net/mailarchive/html/elecraft-list/2005-08/msg00562.html?
> Does that create potential stability problems also?
>
> I've got this link on my K2 mods page and just wanted to make sure I can
> recommend it and keep it there. I have never had any problems
> with BFO range
> myself so I have no personal experience with this myself.
>
> 73
>
> Sverre
> LA3ZA
> http://www.qslnet.de/la3za/
>

Don Brown-4

Re: RE: K2 BFO Test

Hi Don and All

I have used this method on 3 or 4 of the K2's I have built. I use a 1pF or
2pF NPO cap to lower the bottom end of the range to get it to meet the spec.
I agree with you on pulling the crystal much with this method. I would not
recommend cap values above maybe 3 or 4 pF. I have never needed more than 1
pf. Padding C173 and C174 is a better method if the radio needs more than 1
or 2 pf. I believe this method was suggested by Gary at Elecraft some time
back. At any rate it is a little easier to do than the padding or change out
of C174 and C173

The other Don

Don Brown
KD5NDB

----- Original Message -----
From: "Don Wilhelm" <[hidden email]>
To: <[hidden email]>; <[hidden email]>; <[hidden email]>
Sent: Thursday, December 08, 2005 5:03 PM
Subject: RE: RE: [Elecraft] K2 BFO Test

> Sverre,
>
> I have not tried that small capacitor from the junction of the crystals
> and
> L33 so I cannot comment on it from that standpoint.
>
> What I would like to state is that when one pulls a crystal by any method,
> the stability becomes worse as the amount of pulling becomes greater. One
> should be aware of this and related facts when modifying any circuit in a
> way that is not 'approved and tested'. Also due to the nature of
> crystals,
> something that happens to work in one situation may not work the same for
> all cases. Remember that I am only bringing up cautions here, I am not
> makeing a firm statement about the operation one way or another.
>
> It certainly would be nice if someone (or better yet, several someones)
> with
> access to suitable instrumentation could try this or any other mod and
> report the results. The fact that it worked on a sample of one does not
> create a statement that it will work in other cases - that is simple
> statistical knowledge - I would like to see something that says it works
> in
> at least 5 or 10 trials before drawing any firm conclusions.
>
> So, yes I think it should be left on your website, but you may want to put
> a
> "Use at your own peril" disclaimer on all those that are not 'approved by
> Elecraft' or otherwise adequately tested (and I invite you to add any of
> my
> mods to that group as well, even though I have absolute confidence in my
> own
> work).
>
> 73,
> Don W3FPR
>
> > -----Original Message-----
> > >
> > > The preferred method of padding the BFO capacitors is to
> > > maintain the ratio between C173 and C174 by paralleling them
> > > with capacitors. A single capacitor from the junction to
> > > ground will be in parallel with the series combination of
> > > C173 and the varactor D38 and could make the BFO less stable
> > > than it should be.
> > >
> >
> > Don,
> >
> > How about a single capacitor (1-4 pF) from the junction of the
> > crystals and
> > the L33 inductor as in
> > http://www.ac6rm.net/mailarchive/html/elecraft-list/2005-08/msg00562.html?
> > Does that create potential stability problems also?
> >
> > I've got this link on my K2 mods page and just wanted to make sure I can
> > recommend it and keep it there. I have never had any problems
> > with BFO range
> > myself so I have no personal experience with this myself.
> >
> > 73
> >
> > Sverre
> > LA3ZA
> > http://www.qslnet.de/la3za/
> >
>
> _______________________________________________
> Elecraft mailing list
> Post to: [hidden email]
> You must be a subscriber to post to the list.
> Subscriber Info (Addr. Change, sub, unsub etc.):
> http://mailman.qth.net/mailman/listinfo/elecraft
>
> Help: http://mailman.qth.net/subscribers.htm
> Elecraft web page: http://www.elecraft.com
>

Don Wilhelm-3

RE: RE: K2 BFO Test

Don B.

Thanks for that information - it adds credibility to that method along with
a good dose of common sense.

Don W. W3FPR

> -----Original Message-----
>
> Hi Don and All
>
> I have used this method on 3 or 4 of the K2's I have built. I use
> a 1pF or
> 2pF NPO cap to lower the bottom end of the range to get it to
> meet the spec.
> I agree with you on pulling the crystal much with this method. I
> would not
> recommend cap values above maybe 3 or 4 pF. I have never needed
> more than 1
> pf. Padding C173 and C174 is a better method if the radio needs
> more than 1
> or 2 pf. I believe this method was suggested by Gary at Elecraft
> some time
> back. At any rate it is a little easier to do than the padding or
> change out
> of C174 and C173
>
>
> The other Don
>
> Don Brown
> KD5NDB
>
>
>
> ----- Original Message -----
> From: "Don Wilhelm" <[hidden email]>
> To: <[hidden email]>; <[hidden email]>; <[hidden email]>
> Sent: Thursday, December 08, 2005 5:03 PM
> Subject: RE: RE: [Elecraft] K2 BFO Test
>
>
> > Sverre,
> >
> > I have not tried that small capacitor from the junction of the crystals
> > and
> > L33 so I cannot comment on it from that standpoint.
> >
> > What I would like to state is that when one pulls a crystal by
> any method,
> > the stability becomes worse as the amount of pulling becomes
> greater. One
> > should be aware of this and related facts when modifying any
> circuit in a
> > way that is not 'approved and tested'. Also due to the nature of
> > crystals,
> > something that happens to work in one situation may not work
> the same for
> > all cases. Remember that I am only bringing up cautions here, I am not
> > makeing a firm statement about the operation one way or another.
> >
> > It certainly would be nice if someone (or better yet, several someones)
> > with
> > access to suitable instrumentation could try this or any other mod and
> > report the results. The fact that it worked on a sample of one does not
> > create a statement that it will work in other cases - that is simple
> > statistical knowledge - I would like to see something that says
> it works
> > in
> > at least 5 or 10 trials before drawing any firm conclusions.
> >
> > So, yes I think it should be left on your website, but you may
> want to put
> > a
> > "Use at your own peril" disclaimer on all those that are not
> 'approved by
> > Elecraft' or otherwise adequately tested (and I invite you to
> add any of
> > my
> > mods to that group as well, even though I have absolute
> confidence in my
> > own
> > work).
> >
> > 73,
> > Don W3FPR
> >
> > > -----Original Message-----
> > > >
> > > > The preferred method of padding the BFO capacitors is to
> > > > maintain the ratio between C173 and C174 by paralleling them
> > > > with capacitors. A single capacitor from the junction to
> > > > ground will be in parallel with the series combination of
> > > > C173 and the varactor D38 and could make the BFO less stable
> > > > than it should be.
> > > >
> > >
> > > Don,
> > >
> > > How about a single capacitor (1-4 pF) from the junction of the
> > > crystals and
> > > the L33 inductor as in
> > >

http://www.ac6rm.net/mailarchive/html/elecraft-list/2005-08/msg00562.html?

> > Does that create potential stability problems also?
> >
> > I've got this link on my K2 mods page and just wanted to make sure I can
> > recommend it and keep it there. I have never had any problems
> > with BFO range
> > myself so I have no personal experience with this myself.
> >
> > 73
> >
> > Sverre
> > LA3ZA
> > http://www.qslnet.de/la3za/
> >
>
> _______________________________________________
> Elecraft mailing list
> Post to: [hidden email]
> You must be a subscriber to post to the list.
> Subscriber Info (Addr. Change, sub, unsub etc.):
> http://mailman.qth.net/mailman/listinfo/elecraft
>
> Help: http://mailman.qth.net/subscribers.htm
> Elecraft web page: http://www.elecraft.com
>

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Bill Coleman-2

Re: K2 BFO Test

In reply to this post by Don Brown-4

On Dec 9, 2005, at 8:56 AM, Don Brown wrote:

> I have used this method on 3 or 4 of the K2's I have built. I use a
> 1pF or
> 2pF NPO cap to lower the bottom end of the range to get it to meet
> the spec.
> I agree with you on pulling the crystal much with this method. I
> would not
> recommend cap values above maybe 3 or 4 pF. I have never needed
> more than 1
> pf. Padding C173 and C174 is a better method if the radio needs
> more than 1
> or 2 pf. I believe this method was suggested by Gary at Elecraft
> some time
> back. At any rate it is a little easier to do than the padding or
> change out
> of C174 and C173

To get the BFO range I needed for RTTY, not only did I have to pad
C173 and 4, but after I had added maximum capacitance there, I went
ahead and added 2 pF to pull the crystal. I have not noticed any
stability problems, and the BFO range is just about perfect.

Bill Coleman, AA4LR, PP-ASEL Mail: [hidden email]
Quote: "Not within a thousand years will man ever fly!"
-- Wilbur Wright, 1901

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