K1 on 10 meters: helpful advice

[wayne burdick]

Stephanie (and other interested parties),

I have some additional thoughts on modifying the K1 for 10 meters. I
also found some old e-mail from another customer who attempted it.
Between the two, I believe you'll be able to do this successfully.

When I designed the Norcal/Wilderness Sierra, which uses the same I.F.
as the K1, I realized that a 36-MHz crystal would be expensive, so I
came up with an alternate mixing scheme where the LO is below the band
rather than above it. The RX and TX image rejection isn't quite as good
with this technique, but that probably doesn't matter since the
band-pass filters are narrow.

Here's the normal conversion scheme (high-side injection):

    RF   28.000 - 28.100
  + IF    4.915
------------------------
  = LO   32.915 - 33.015
+ VFO    3.085 -  2.985
------------------------
  = XO   36.000


Here's the alternate scheme using low-side injection:

    RF   28.000 - 28.100
  - IF    4.915
------------------------
  = LO   23.085 - 23.185
+ VFO    3.085 -  2.985
------------------------
  = XO   26.170

I.e., you can use a 26.170 MHz fundamental crystal. Advantages of this
frequency vs. 36 MHz include: (1) more power output from the NE602
premixer oscillator; (2) cheaper; (3) possibly available from
Wilderness Radio. If Wilderness doesn't have any, you might try ICM. I
think the ICM part number for the basic crystal type (not including
frequency) would be #436162.

Low-side injection results in one additional minor issue: the sideband
gets inverted. This just means that the CW pitch will change in the
opposite way from the other bands as you tune. VFO readings should
still be accurate.

Looking back through old K1 design notes, I found an e-mail from
another customer (Bob Larkin, [hidden email]) who put his K1 on 10
meters. He used an overtone 36 MHz oscillator, requiring changes to the
basic band module. A 26.17-MHz crystal would be simpler, as I described
above. But Bob's notes on getting adequate power output on this band
are quite useful. I have attached them below. Let me know if you try
this! If we have a couple of customers successfully complete the mods,
we'll offer it as an option kit for use with the 2-band module.

73,
Wayne
N6KR

* * *

The RF filter was designed to have 2.2 dB IL in 50 Ohms and has 3 and
40 dB
bandwidths of 1.8 and 18.5 MHz. Inductor were the regular 1 uH.
C16=C20=270
pF, C17=C19=33 pF, C18=1.5pF (if the latter is not available, use 0.75
inches of the gimmick capacitor).

The LPF is an interesting topic. I did not try a direct scaling of the
other
filters. This might work adequately, and would be good for someone to
try.
Instead I designed a 2-coil modified elliptic filter. The goal was to
move
the cutoff frequency far enough above 28 MHz to minimize the insertion
loss,
and to put an elliptic null at the second harmonic, 56 MHz. The final
design
cutoff at 34.9 MHz and had a measured insertion loss of 0.17 dB at 28
MHz
and 65 dB at 56 MHz. L11 is 0.28uH (9T T37-6, over 75%), L12 is 0.22uH
(7T
T37-6, tight wound--probably should be 8T spread out). C24=94 pF (two
47 pF
in parallel, one on top, one under), C25=164 pF (two 82 pF), C26=75 pF.
The
capacitors in parallel with the inductors are mounted below the board
and
arranged to be flat against the board to clear the bottom board parts.
Across L11 is 13 pF (two 6.8 pF in parallel), across L12 is 36 pF. This
is
quite a few parts, but the measured performance is great.

Now the K1 was on 10-m, but the transmitter didn't put out any power!
There
wasn't enough drive to make the Class C Q7 draw current. I made two
changes
to fix this. Both of these have the potential to alter the performance
on
other bands, particularly 15 and 20-m. I attempted to evaluate these
effects, but I only have the one K1! Both changes are attempting to
compensate for the drop in gain of Q6 and Q7 with frequency. My 10-m
performance seems to still be limited by drive to Q7.

First, U9 has more gain available. I put 270 pF across R11, boosting the
gain on all bands above 40-m.

This produced a fraction of a Watt, but not enough drive, yet. So, I
measured the impedance looking into pin 8 of J7, in transmit. At 28 MHz,
this was 5+j8 Ohms. So I added an L-network to match this closer to 50
Ohms.
At the J7-P8 side of D9, I inserted a .12uH (6T #32 on T12-6, tight)
and on
the J7-8 end put 200 pF to ground.

Now at 13.8 V I get 3W, and at 12V about 1W. All spurs are at least 48
dBc.

As a by-product the output on 15-m is easily 7W. The power control
seems to
still be able to work fine and on my K1 the spurs were still essentially
where they were on all bands.



---

http://www.elecraft.com

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[Stephanie Maks]

Hi Wayne,

Thanks very much for the additional information!  Most of my  
guestimated values for the 2-band board seem to match those that were  
in the email you sent; the only ones I was way off on were C16 & C20.

I actually found a cheap source of fundamental 36MHz crystals.  
They're about $4.00 each, the only catch is they're surface-mount.  I  
just solder leads on them and use them in the normal crystal mounting  
holes.

Yesterday I was at work most of the day with a lot of time to think  
and surf the net, and found one email that I'd missed in my earlier  
research:
http://www.ac6rm.net/mailarchive/html/elecraft-list/2003-06/ 
msg00789.html

Based on that email, I reduced the value of RF-R11 from 82 ohms to 33  
ohms.  I now get up to almost 3 watts out on 10 meters.  I'll have a  
go at adding the L-network at J7-P8 as described in the email you  
provided and see if that improves things any further.

I also went a little crazy last night with experimentation, and  
decided to have a shot at my 'ideal' 4-band filter board:  80 / 40 /  
20 / 10 meters. I've got a design in mind to provide 4 separate low-
pass filters, but it will mean some drastic surgery to the filter  
board, and I won't have room for the noise blanker any more.  As it  
stands now, on the test bench, I have a full 5 watts output on 80,  
40, and 20 meters, and 2 to 3 watts on 10 meters.  The board's two  
existing low pass filters are set-up for 40 and 10 meters.  So while  
I can currently listen on all four bands, I won't be transmitting on  
80 or 20 just yet.  The key for me though is, I know what is  
required, what the values are, and have a good idea how to lay it out  
physically, so basically I know it's possible.

Thanks again for the info and suggestions!

Happy holidays and 73 de
Stephanie Maks
va3uxb



On 26-Dec-2005, at 14.44.01, wayne burdick wrote:

> Stephanie (and other interested parties),
>
> I have some additional thoughts on modifying the K1 for 10 meters.  
> I also found some old e-mail from another customer who attempted  
> it. Between the two, I believe you'll be able to do this successfully.
>
> When I designed the Norcal/Wilderness Sierra, which uses the same  
> I.F. as the K1, I realized that a 36-MHz crystal would be  
> expensive, so I came up with an alternate mixing scheme where the  
> LO is below the band rather than above it. The RX and TX image  
> rejection isn't quite as good with this technique, but that  
> probably doesn't matter since the band-pass filters are narrow.
>
> Here's the normal conversion scheme (high-side injection):
>
>    RF   28.000 - 28.100
>  + IF    4.915
> ------------------------
>  = LO   32.915 - 33.015
> + VFO    3.085 -  2.985
> ------------------------
>  = XO   36.000
>
>
> Here's the alternate scheme using low-side injection:
>
>    RF   28.000 - 28.100
>  - IF    4.915
> ------------------------
>  = LO   23.085 - 23.185
> + VFO    3.085 -  2.985
> ------------------------
>  = XO   26.170
>
> I.e., you can use a 26.170 MHz fundamental crystal. Advantages of  
> this frequency vs. 36 MHz include: (1) more power output from the  
> NE602 premixer oscillator; (2) cheaper; (3) possibly available from  
> Wilderness Radio. If Wilderness doesn't have any, you might try  
> ICM. I think the ICM part number for the basic crystal type (not  
> including frequency) would be #436162.
>
> Low-side injection results in one additional minor issue: the  
> sideband gets inverted. This just means that the CW pitch will  
> change in the opposite way from the other bands as you tune. VFO  
> readings should still be accurate.
>
> Looking back through old K1 design notes, I found an e-mail from  
> another customer (Bob Larkin, [hidden email]) who put his K1  
> on 10 meters. He used an overtone 36 MHz oscillator, requiring  
> changes to the basic band module. A 26.17-MHz crystal would be  
> simpler, as I described above. But Bob's notes on getting adequate  
> power output on this band are quite useful. I have attached them  
> below. Let me know if you try this! If we have a couple of  
> customers successfully complete the mods, we'll offer it as an  
> option kit for use with the 2-band module.
>
> 73,
> Wayne
> N6KR
>
> * * *
>
> The RF filter was designed to have 2.2 dB IL in 50 Ohms and has 3  
> and 40 dB
> bandwidths of 1.8 and 18.5 MHz. Inductor were the regular 1 uH.  
> C16=C20=270
> pF, C17=C19=33 pF, C18=1.5pF (if the latter is not available, use 0.75
> inches of the gimmick capacitor).
>
> The LPF is an interesting topic. I did not try a direct scaling of  
> the other
> filters. This might work adequately, and would be good for someone  
> to try.
> Instead I designed a 2-coil modified elliptic filter. The goal was  
> to move
> the cutoff frequency far enough above 28 MHz to minimize the  
> insertion loss,
> and to put an elliptic null at the second harmonic, 56 MHz. The  
> final design
> cutoff at 34.9 MHz and had a measured insertion loss of 0.17 dB at  
> 28 MHz
> and 65 dB at 56 MHz. L11 is 0.28uH (9T T37-6, over 75%), L12 is  
> 0.22uH (7T
> T37-6, tight wound--probably should be 8T spread out). C24=94 pF  
> (two 47 pF
> in parallel, one on top, one under), C25=164 pF (two 82 pF), C26=75  
> pF. The
> capacitors in parallel with the inductors are mounted below the  
> board and
> arranged to be flat against the board to clear the bottom board parts.
> Across L11 is 13 pF (two 6.8 pF in parallel), across L12 is 36 pF.  
> This is
> quite a few parts, but the measured performance is great.
>
> Now the K1 was on 10-m, but the transmitter didn't put out any  
> power! There
> wasn't enough drive to make the Class C Q7 draw current. I made two  
> changes
> to fix this. Both of these have the potential to alter the  
> performance on
> other bands, particularly 15 and 20-m. I attempted to evaluate these
> effects, but I only have the one K1! Both changes are attempting to
> compensate for the drop in gain of Q6 and Q7 with frequency. My 10-m
> performance seems to still be limited by drive to Q7.
>
> First, U9 has more gain available. I put 270 pF across R11,  
> boosting the
> gain on all bands above 40-m.
>
> This produced a fraction of a Watt, but not enough drive, yet. So, I
> measured the impedance looking into pin 8 of J7, in transmit. At 28  
> MHz,
> this was 5+j8 Ohms. So I added an L-network to match this closer to  
> 50 Ohms.
> At the J7-P8 side of D9, I inserted a .12uH (6T #32 on T12-6,  
> tight) and on
> the J7-8 end put 200 pF to ground.
>
> Now at 13.8 V I get 3W, and at 12V about 1W. All spurs are at least  
> 48 dBc.
>
> As a by-product the output on 15-m is easily 7W. The power control  
> seems to
> still be able to work fine and on my K1 the spurs were still  
> essentially
> where they were on all bands.
>
>
>
> ---
>
> http://www.elecraft.com
>

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[Sandy W5TVW]

Keep us posted on this guys!  I plan ultimately to build a 17/10 meter board.
Already have a 160/80 meter board to go with my 40/30/20/15 meter
4 band board.
I'm in no rush as it will be a while before 10 gets "decent" again except for
the usual summertime "Sporadic E" type stuff and the perennial
North-South path to South America.  I can work the Argentine/Brazilian
Venezuelan stations already on 20 or 15 so don't need 10 meters for them!
73,
Sandy W5TVW
----- Original Message -----
From: "Stephanie Maks" <[hidden email]>
To: "wayne burdick" <[hidden email]>
Cc: "Elecraft Reflector" <[hidden email]>
Sent: Monday, December 26, 2005 3:30 PM
Subject: [Elecraft] Re: K1 on 10 meters: helpful advice


| Hi Wayne,
|
| Thanks very much for the additional information!  Most of my  
| guestimated values for the 2-band board seem to match those that were  
| in the email you sent; the only ones I was way off on were C16 & C20.
|
| I actually found a cheap source of fundamental 36MHz crystals.  
| They're about $4.00 each, the only catch is they're surface-mount.  I  
| just solder leads on them and use them in the normal crystal mounting  
| holes.
|
| Yesterday I was at work most of the day with a lot of time to think  
| and surf the net, and found one email that I'd missed in my earlier  
| research:
| http://www.ac6rm.net/mailarchive/html/elecraft-list/2003-06/ 
| msg00789.html
|
| Based on that email, I reduced the value of RF-R11 from 82 ohms to 33  
| ohms.  I now get up to almost 3 watts out on 10 meters.  I'll have a  
| go at adding the L-network at J7-P8 as described in the email you  
| provided and see if that improves things any further.
|
| I also went a little crazy last night with experimentation, and  
| decided to have a shot at my 'ideal' 4-band filter board:  80 / 40 /  
| 20 / 10 meters. I've got a design in mind to provide 4 separate low-
| pass filters, but it will mean some drastic surgery to the filter  
| board, and I won't have room for the noise blanker any more.  As it  
| stands now, on the test bench, I have a full 5 watts output on 80,  
| 40, and 20 meters, and 2 to 3 watts on 10 meters.  The board's two  
| existing low pass filters are set-up for 40 and 10 meters.  So while  
| I can currently listen on all four bands, I won't be transmitting on  
| 80 or 20 just yet.  The key for me though is, I know what is  
| required, what the values are, and have a good idea how to lay it out  
| physically, so basically I know it's possible.
|
| Thanks again for the info and suggestions!
|
| Happy holidays and 73 de
| Stephanie Maks
| va3uxb
|
|
|
| On 26-Dec-2005, at 14.44.01, wayne burdick wrote:
|
| > Stephanie (and other interested parties),
| >
| > I have some additional thoughts on modifying the K1 for 10 meters.  
| > I also found some old e-mail from another customer who attempted  
| > it. Between the two, I believe you'll be able to do this successfully.
| >
| > When I designed the Norcal/Wilderness Sierra, which uses the same  
| > I.F. as the K1, I realized that a 36-MHz crystal would be  
| > expensive, so I came up with an alternate mixing scheme where the  
| > LO is below the band rather than above it. The RX and TX image  
| > rejection isn't quite as good with this technique, but that  
| > probably doesn't matter since the band-pass filters are narrow.
| >
| > Here's the normal conversion scheme (high-side injection):
| >
| >    RF   28.000 - 28.100
| >  + IF    4.915
| > ------------------------
| >  = LO   32.915 - 33.015
| > + VFO    3.085 -  2.985
| > ------------------------
| >  = XO   36.000
| >
| >
| > Here's the alternate scheme using low-side injection:
| >
| >    RF   28.000 - 28.100
| >  - IF    4.915
| > ------------------------
| >  = LO   23.085 - 23.185
| > + VFO    3.085 -  2.985
| > ------------------------
| >  = XO   26.170
| >
| > I.e., you can use a 26.170 MHz fundamental crystal. Advantages of  
| > this frequency vs. 36 MHz include: (1) more power output from the  
| > NE602 premixer oscillator; (2) cheaper; (3) possibly available from  
| > Wilderness Radio. If Wilderness doesn't have any, you might try  
| > ICM. I think the ICM part number for the basic crystal type (not  
| > including frequency) would be #436162.
| >
| > Low-side injection results in one additional minor issue: the  
| > sideband gets inverted. This just means that the CW pitch will  
| > change in the opposite way from the other bands as you tune. VFO  
| > readings should still be accurate.
| >
| > Looking back through old K1 design notes, I found an e-mail from  
| > another customer (Bob Larkin, [hidden email]) who put his K1  
| > on 10 meters. He used an overtone 36 MHz oscillator, requiring  
| > changes to the basic band module. A 26.17-MHz crystal would be  
| > simpler, as I described above. But Bob's notes on getting adequate  
| > power output on this band are quite useful. I have attached them  
| > below. Let me know if you try this! If we have a couple of  
| > customers successfully complete the mods, we'll offer it as an  
| > option kit for use with the 2-band module.
| >
| > 73,
| > Wayne
| > N6KR
| >
| > * * *
| >
| > The RF filter was designed to have 2.2 dB IL in 50 Ohms and has 3  
| > and 40 dB
| > bandwidths of 1.8 and 18.5 MHz. Inductor were the regular 1 uH.  
| > C16=C20=270
| > pF, C17=C19=33 pF, C18=1.5pF (if the latter is not available, use 0.75
| > inches of the gimmick capacitor).
| >
| > The LPF is an interesting topic. I did not try a direct scaling of  
| > the other
| > filters. This might work adequately, and would be good for someone  
| > to try.
| > Instead I designed a 2-coil modified elliptic filter. The goal was  
| > to move
| > the cutoff frequency far enough above 28 MHz to minimize the  
| > insertion loss,
| > and to put an elliptic null at the second harmonic, 56 MHz. The  
| > final design
| > cutoff at 34.9 MHz and had a measured insertion loss of 0.17 dB at  
| > 28 MHz
| > and 65 dB at 56 MHz. L11 is 0.28uH (9T T37-6, over 75%), L12 is  
| > 0.22uH (7T
| > T37-6, tight wound--probably should be 8T spread out). C24=94 pF  
| > (two 47 pF
| > in parallel, one on top, one under), C25=164 pF (two 82 pF), C26=75  
| > pF. The
| > capacitors in parallel with the inductors are mounted below the  
| > board and
| > arranged to be flat against the board to clear the bottom board parts.
| > Across L11 is 13 pF (two 6.8 pF in parallel), across L12 is 36 pF.  
| > This is
| > quite a few parts, but the measured performance is great.
| >
| > Now the K1 was on 10-m, but the transmitter didn't put out any  
| > power! There
| > wasn't enough drive to make the Class C Q7 draw current. I made two  
| > changes
| > to fix this. Both of these have the potential to alter the  
| > performance on
| > other bands, particularly 15 and 20-m. I attempted to evaluate these
| > effects, but I only have the one K1! Both changes are attempting to
| > compensate for the drop in gain of Q6 and Q7 with frequency. My 10-m
| > performance seems to still be limited by drive to Q7.
| >
| > First, U9 has more gain available. I put 270 pF across R11,  
| > boosting the
| > gain on all bands above 40-m.
| >
| > This produced a fraction of a Watt, but not enough drive, yet. So, I
| > measured the impedance looking into pin 8 of J7, in transmit. At 28  
| > MHz,
| > this was 5+j8 Ohms. So I added an L-network to match this closer to  
| > 50 Ohms.
| > At the J7-P8 side of D9, I inserted a .12uH (6T #32 on T12-6,  
| > tight) and on
| > the J7-8 end put 200 pF to ground.
| >
| > Now at 13.8 V I get 3W, and at 12V about 1W. All spurs are at least  
| > 48 dBc.
| >
| > As a by-product the output on 15-m is easily 7W. The power control  
| > seems to
| > still be able to work fine and on my K1 the spurs were still  
| > essentially
| > where they were on all bands.
| >
| >
| >
| > ---
| >
| > http://www.elecraft.com
| >
|
| _______________________________________________
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|
|
|
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