10M birdie and other assundries

[Julius Fazekas n2wn]

Just out of curiousity, after spending some time on
10M during ARRL 10, I noticed a birdie around
28.019/20. Is there a way to eliminate this or move it
below 28.000?

As to my high current draw on 160, the KPA100 works
fine into a dummy load and straight into the antenna.
It does seem to draw more with the KAT100 in the
circuit. I can't imagine much in the tuner that would
cause such a problem (although I could be wrong). My
thoughts drift towards a ground loop issue and/or rf
getting back into the rig's control circuit. Guess I
will be adding some further current chokes in the
shack...

Best wishes to all for the holiday season. May 2007 be
good to you and yours...

Cheers,
Julius
n2wn
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[Tom Althoff]

Hi Jules!

I have a temporary workaround that I use...albeit a pain in the butt one.

That birdy seems related to an oscillator in the KPA-100 (HV PS?)..although
Don can be probably be more specific.

I've found that by turning the power level down that the birdy shifts a bit
in frequency...maybe a few kHz.   Enough to make a difference between
hearing a station and not.

If a new country is sitting on 29.020 I'll twiddle the power level between
transmissions...otherwise I avoid that frequncy during normal operation.

73 de Tom K2TA

----- Original Message -----
From: "J F" <[hidden email]>
To: <[hidden email]>
Sent: Tuesday, December 19, 2006 8:21 AM
Subject: [Elecraft] 10M birdie and other assundries

> Just out of curiousity, after spending some time on
> 10M during ARRL 10, I noticed a birdie around
> 28.019/20. Is there a way to eliminate this or move it
> below 28.000?
>
> As to my high current draw on 160, the KPA100 works
> fine into a dummy load and straight into the antenna.
> It does seem to draw more with the KAT100 in the
> circuit. I can't imagine much in the tuner that would
> cause such a problem (although I could be wrong). My
> thoughts drift towards a ground loop issue and/or rf
> getting back into the rig's control circuit. Guess I
> will be adding some further current chokes in the
> shack...
>
> Best wishes to all for the holiday season. May 2007 be
> good to you and yours...
>
> Cheers,
> Julius
> n2wn
> _______________________________________________
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[pc5m, Carel]

Julius, I also strugled with this and made a small Excel file to calculate
at which frequency this birdie will be. File can be found at:
www.pc5m.com\projects\resources\kpa100_xtal.xls

At the top you can input the x-tal freq used in the KPA100 and below it
will calculate the mixing products (up to 5th level). If a cell turn red
than the spur will be in-band !

It turns out that NO x-tal (in the vicinity of original one) will provide
birdie free operation on all bands, but depending on your preference you
can position this birdie on the bands/frequencie best for you.

In my case I changed the x-tal to 16.0 MHz

gl,

Carel, pc5m


-------------------
Just out of curiousity, after spending some time on
10M during ARRL 10, I noticed a birdie around
28.019/20. Is there a way to eliminate this or move it
below 28.000?

As to my high current draw on 160, the KPA100 works
fine into a dummy load and straight into the antenna.
It does seem to draw more with the KAT100 in the
circuit. I can't imagine much in the tuner that would
cause such a problem (although I could be wrong). My
thoughts drift towards a ground loop issue and/or rf
getting back into the rig's control circuit. Guess I
will be adding some further current chokes in the
shack...

Best wishes to all for the holiday season. May 2007 be
good to you and yours...

Cheers,
Julius
n2wn


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[Vic K2VCO]

J F wrote:
> Just out of curiousity, after spending some time on
> 10M during ARRL 10, I noticed a birdie around
> 28.019/20. Is there a way to eliminate this or move it
> below 28.000?

Yes, but even I haven't had the guts to implement it.

Replace the diode t/r switch with a reed relay such as the Matsushita
RSD12V.    Reduce the power level of the bias oscillator and remove the
high voltage multiplier section so you can get -12v for the RS232
interface with less stray RF floating around.  Alternatively, find a way
to power it from the computer (and some RS232 ports will apparently work
without the -12v at all), so the bias oscillator can be completely disabled.

I tried various forms of shielding, filtering and bypassing without
success.  A friend pointed out to me that the birdie is a result of
mixing between VHF harmonics of this and another oscillator in the K2,
so that explains why it's so hard to kill.
--
73,
Vic, K2VCO
Fresno CA
http://www.qsl.net/k2vco
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[Vic K2VCO]

Vic K2VCO wrote:

> Replace the diode t/r switch with a reed relay

I should have specified that I was talking about the t/r switch in the
KPA100, not the QRP K2, of course.
--
73,
Vic, K2VCO
Fresno CA
http://www.qsl.net/k2vco
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[Michael Pfeuffer]

Anyone know if remoting the KPA100 to an EC-2 case reduces the birdie?

--Mike


At 10:32 AM 12/19/2006, Vic K2VCO wrote:

>J F wrote:
>>Just out of curiousity, after spending some time on
>>10M during ARRL 10, I noticed a birdie around
>>28.019/20. Is there a way to eliminate this or move it
>>below 28.000?
>
>Yes, but even I haven't had the guts to implement it.
>
>Replace the diode t/r switch with a reed relay such as the Matsushita
>RSD12V.    Reduce the power level of the bias oscillator and remove the
>high voltage multiplier section so you can get -12v for the RS232
>interface with less stray RF floating around.  Alternatively, find a way
>to power it from the computer (and some RS232 ports will apparently work
>without the -12v at all), so the bias oscillator can be completely disabled.
>
>I tried various forms of shielding, filtering and bypassing without
>success.  A friend pointed out to me that the birdie is a result of mixing
>between VHF harmonics of this and another oscillator in the K2, so that
>explains why it's so hard to kill.
>--
>73,
>Vic, K2VCO
>Fresno CA
>http://www.qsl.net/k2vco
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[Geoffrey Mackenzie-Kennedy-2]

Hi Julius,

If the birdie at 28.019/20 MHz changes frequency when you change the
transmitter power demand from <10w to >10w, then the KPA100's HV Bias
oscillator is involved. Vic, K2VCO, and I had an off list discussion some
time ago about birdies including this one, and though Vic found the birdie I
did not because his HV Bias oscillator runs at 18.434 MHz while I have opted
to keep mine at 16.293 MHz for reasons other than birdies. If I remember
correctly this particular birdie involves not only the HV Bias oscillator
but also another oscillator in the K2 which mix to produce a signal at a
spurious response frequency of the receiver when tuned to 28.019 MHz. I'll
have to look up my notes.

You can move this 10m birdie to another frequency by changing the HV Bias
oscillator frequency although the options for all band freedom from birdies
involving this source are limited. In my K2/100 the bias oscillator signal
enters the K2 via the ribbon cable, which can be 'choked' with a clamp on
ferrite, and the loudspeaker leads which can be removed from the KPA100
board where the trace acts as a link, but be advised that these last two
mods might not work with all K2/100s. Later on I repackaged the HV Bias
oscillator and voltage multiplier in a shielded box, with pi configuration
filters on all DC lines to kill the problem at source.

73,
Geoff
GM4ESD


----- Original Message -----
From: "J F" <[hidden email]>
To: <[hidden email]>
Sent: Tuesday, December 19, 2006 1:21 PM
Subject: [Elecraft] 10M birdie and other assundries


> Just out of curiousity, after spending some time on
> 10M during ARRL 10, I noticed a birdie around
> 28.019/20. Is there a way to eliminate this or move it
> below 28.000?

<snip>



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[Michael E. Dobson]

I don't know how reduced it is because I haven't compared it to the
KPA100 as the top lid but it is barely noticeable in my K2 with the
KPA100 in an EC2 unless I have the preamp on.  Even then, it is more
a nuisance than a problem unless the signal is very weak.

73,
Mike WA3KYY

At 11:58 AM 12/19/2006, you wrote:

>Anyone know if remoting the KPA100 to an EC-2 case reduces the birdie?
>
>--Mike
>
>
>At 10:32 AM 12/19/2006, Vic K2VCO wrote:
>>J F wrote:
>>>Just out of curiousity, after spending some time on
>>>10M during ARRL 10, I noticed a birdie around
>>>28.019/20. Is there a way to eliminate this or move it
>>>below 28.000?
>>
>>Yes, but even I haven't had the guts to implement it.
>>
>>Replace the diode t/r switch with a reed relay such as the
>>Matsushita RSD12V.    Reduce the power level of the bias oscillator
>>and remove the high voltage multiplier section so you can get -12v
>>for the RS232 interface with less stray RF floating
>>around.  Alternatively, find a way to power it from the computer
>>(and some RS232 ports will apparently work without the -12v at
>>all), so the bias oscillator can be completely disabled.
>>
>>I tried various forms of shielding, filtering and bypassing without
>>success.  A friend pointed out to me that the birdie is a result of
>>mixing between VHF harmonics of this and another oscillator in the
>>K2, so that explains why it's so hard to kill.
>>--
>>73,
>>Vic, K2VCO
>>Fresno CA
>>http://www.qsl.net/k2vco
>>_______________________________________________
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>
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[DaveL G3TJP]

Sorry to be a wet blanket, but from my current standpoint, I'd be grateful to find just the one spurious signal from the KPA.

I have literally dozens of spurii on all bands that are S2 or greater.  Some read S9+40 and would read higher if the S-meter could indicate that.

They all emanate from that dratted HV bias supply and moving between high and low power on the K2's power control doesn't affect the birdie count.  I haven't found any that move, either.  Turning off Q8, the bias supply osc. transistor, turns off all the spurii.

All components have been checked most carefully for value and all have been re-soldered.  The KPA was constructed to the latest revision and with R4 at 100k, the bias voltage was just over 140v.  Increasing R4 to 220k has dropped the bias voltage to 128v, but hasn't reduced the spurii.  They are not entering the K2 via the speaker lead, aux. power or RF connections but are present at rock-crushing levels with just the ribbon cable connected.

It's been a great disappointment to find this problem, as everything else has worked beautifully (after minor debugging).  I note the various comments regarding the difficulties experienced by others in their attempts to "tame" the situation, so with my limited expertise, I don't hold out a lot of hope.  Just in case it's the MAX1406, I'll try lifting one end of D7 to disconnect its input, but after that I'll probably resort to replacing each and every component in that area one by one, in case there's a "rogue".

73 and Season's Greetings to everyone.

Dave L  G3TJP, who's feeling very sorry for himself just now  ;-(


 Quote:
Julius, N2WN
Just out of curiousity, after spending some time on 10M during ARRL 10, I noticed a birdie around 28.019/20. Is there a way to eliminate this or move it below 28.000?
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[Ben Hofmann K1NT]

If PC5M's calculations are correct, and these birdies
are caused by mixing products of the 4.9136 MHz IF
crystals in the K2 and the 18.432 MHz bias supply
crystal in the KPA100, and assuming his spreadsheet
calculations are correct, it seems that a crystal at
15.8735 MHz (+ or - about 9.5 kHz) would not produce
mixing products in any US ham band (including 5.3305
through 5.4065 MHz for 60m).  Since this is not a
standard crystal frequency, I wonder what the cost
would be of a batch of custom crystals at this
frequency?  It seems that even within general
tolerances for calibration and temperature stability
for both values of crystals this should be feasible.
Like I said, I don't know what the cost of a run of
custom crystals would be, but it may be something for
the folks at Elecraft to look into for future outgoing
KPA100's, and then those of us who wish, could
purchase one as a spare part to retrofit our existing
amps.  Another alternative would be a separate
individual purchasing a batch of custom crystals for
sale to Elecraft users.  Just a thought.  What do you
all think?

-Ben  K1NT
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[wayne burdick]

When we designed the crystal oscillators in question (KIO2, KPA100), we
did extensive testing using dozens of crystal frequencies to find the
optimal ones. The frequencies presently in use are as good as anything
else that might be tried, I believe, unless you have a specific issue
that can be dealt with by moving an oscillator a short distance.

If someone wants to experiment with this, they should keep in mind that
spurious signal search can start on paper, but then must be done on the
K2 itself, in both RX and TX modes, across all bands. In TX mode this
is cumbersome: you have to move the VFO a kHz or so, press
TUNE+DISPLAY, check the spectrum analyzer, cancel TUNE, then repeat.
(You can't just spin the VFO knob during TX, unless I write some new
firmware  :)

You have to also be prepared to accept a compromise solution (as we
did), because the mixing process involves harmonics up through high
VHF, making it nearly impossible to eliminate every last ham-band
birdie of any amplitude. To achieve that would require extensive
internal shielding, which would have made the K2 too expensive to be
profitable (for us) and affordable (for you).

Regarding custom crystals: Expect to pay about $10-20 for very small
quantities, depending on how quickly you want them. Cal Crystal is a
good choice. If a very promising alternative frequency is found,
crystals can be bought in large quantities for under $1.

I should mention that there's another, perhaps cleaner way to generate
negative DC supply voltages: use a high-amplitude AF sine wave
oscillator rather than an RF oscillator. This takes a lot more parts,
assuming you want a very pure sinewave that doesn't droop or become
distorted when loaded. I'd suggest a twin-T RC oscillator or a
carefully trimmed op-amp Wein bridge oscillator, followed by a
high-input-impedance buffer and a power amp running from 12 V. You then
have to add a detector similar to the ones used in the KIO2 and KPA100,
but of course the capacitors will be much larger due to the lower drive
frequency. This would certainly not fit on the existing KIO3 PCB; it
would have to be redesign using all SMD parts.

Note that RS232 ICs with on-chip charge-pumps use square waves, not
sine waves. They will create loud, broadband noise across the lower HF
bands unless completely shielded or implemented using very small SMD
components, ideally on a 4-layer board, with extensive I/O and power
supply decoupling.

73,
Wayne
N6KR


---

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[pc5m, Carel]

Hi Ben,

My assumption is that the birdie is due to mixing of the VCO with X-tal
frequencies. At certain a (VCO) frequency it will be such that this mixing
product will produce exactly the IF frequency--> a birdie is born. Of course
will this "certain" VCO frequency correspond with a RF frequency (the
frequency which is on the display of the K2).

Now we need to do some maths....:-)

So the calculation is as follows:
(1) X*Fxtal + Y*Fvco = Fif  (never mind the + sign , minus is also taken
care for by the negative Y values).

Fxtal = KPA100 xtal freq
Fvco = K2 VCO freq
Fif = K2's IF (4.9136 MHz)
X and Y are integers from e.g -4 to + 4, i.e. -4,-3,-2, etc to +4 (number of
mixing products you would like to consider)

Also we do know that Fvco = Frx - Fif (minus will be a plus depending if you
are below or above 17 mtrs)
(2) Fvco = K2 VCO freq
Frx = K2 "displayed" freq
Fif = K2's IF  

With (1) and (2) we can solve this equation:
(3) Frx = Fif + (Fif-X*Fxtal)/Y and (below 17 mtrs)
(4) Frx = -Fif + (Fif-X*Fxtal)/Y (above 17 mtrs)

This is basically what my spreadsheet is showing, it will loop through the
matrix of X and Y values, and calculates Frf depending on the chosen Fxtal
and (fixed) Fif. That is will show this matrix for every band and perform a
conditional format (red) for in band products. The other colors have been an
attempt to show that mixing products with a lower order of X and Y will be
stronger than those with larger numbers, although I did find any proof of
that (somethimes higher order mixing are even stronger than lower..)

And you are correct ! 15.873 would be perfect...

Would really appreciate if someone could take the time and verify above
paradigm.

Gl,

Carel, pc5m


-----Original Message-----
From: [hidden email]
[mailto:[hidden email]] On Behalf Of Ben Hofmann K1NT
Sent: Wednesday, December 20, 2006 8:17 PM
To: [hidden email]
Subject: Re: [Elecraft] 10M birdie and other assundries

If PC5M's calculations are correct, and these birdies
are caused by mixing products of the 4.9136 MHz IF
crystals in the K2 and the 18.432 MHz bias supply
crystal in the KPA100, and assuming his spreadsheet
calculations are correct, it seems that a crystal at
15.8735 MHz (+ or - about 9.5 kHz) would not produce
mixing products in any US ham band (including 5.3305
through 5.4065 MHz for 60m).  Since this is not a
standard crystal frequency, I wonder what the cost
would be of a batch of custom crystals at this
frequency?  It seems that even within general
tolerances for calibration and temperature stability
for both values of crystals this should be feasible.
Like I said, I don't know what the cost of a run of
custom crystals would be, but it may be something for
the folks at Elecraft to look into for future outgoing
KPA100's, and then those of us who wish, could
purchase one as a spare part to retrofit our existing
amps.  Another alternative would be a separate
individual purchasing a batch of custom crystals for
sale to Elecraft users.  Just a thought.  What do you
all think?

-Ben  K1NT
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