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K2: K2/100 birdie @ 3589

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VK7JB

K2: K2/100 birdie @ 3589

Hi All,

I've just finished K2/100 #6998. After blowing the PA transistors of the base K2 by accidentally dropping the frequency probe into the works, I've completed the KPA100, installed it and all is working very well. Made several SSB contacts tonight and I couldn't be happier. I have a great sense of achievement :)

I'm curious about a prominent birdie, zero beat at 3589khz. It's present, and more prominent, with the antenna disconnected and has its origin internally.

There are some postings about this birdie from around 2008, but I don't see any resolution. I can live with it, even though it's inconveniently located right where I like to work on SSB phone. Did anyone work out where this comes from and whether or not there is a simple fix?

Also, I've calibrated the K2 reference oscillator several times according to the N6KR method. The result is that my frequency display is 20hz off frequency after the rig has warmed up: eg it reads 9999.98 for 10000.00 WWV signal. Am I correct in understanding this is about as good I can expect given the DAC parameters of the K2? I can't seem to improve on it further by repeating it.

73,

John
VK7JB

Don Wilhelm-4

Re: K2: K2/100 birdie @ 3589

John,

I have not discovered the source of that birdie, but it is there.

Yes, 20 Hz is the DAC limit in the K2.

73,
Don W3FPR

On 11/2/2010 7:50 AM, VK7JB wrote:

> Hi All,
>
> I've just finished K2/100 #6998. After blowing the PA transistors of the
> base K2 by accidentally dropping the frequency probe into the works, I've
> completed the KPA100, installed it and all is working very well. Made
> several SSB contacts tonight and I couldn't be happier. I have a great
> sense of achievement :)
>
> I'm curious about a prominent birdie, zero beat at 3589khz. It's present,
> and more prominent, with the antenna disconnected and has its origin
> internally.
>
> There are some postings about this birdie from around 2008, but I don't see
> any resolution. I can live with it, even though it's inconveniently located
> right where I like to work on SSB phone. Did anyone work out where this
> comes from and whether or not there is a simple fix?
>
> Also, I've calibrated the K2 reference oscillator several times according to
> the N6KR method. The result is that my frequency display is 20hz off
> frequency after the rig has warmed up: eg it reads 9999.98 for 10000.00 WWV
> signal. Am I correct in understanding this is about as good I can expect
> given the DAC parameters of the K2? I can't seem to improve on it further
> by repeating it.
>
> 73,
>
> John
> VK7JB

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Geoffrey Mackenzie-Kennedy

Re: K2: K2/100 birdie @ 3589

In reply to this post by VK7JB

Hi John,

Glad to hear that after all of your bad luck your K2/100 is now working
well.

The strong birdie at 3589 kHz was also present in my K2/100 before I
embarked on a birdie killing project a few years ago, which involved a fair
amout of difficult surgery. This particular birdie is the result of the
fundamental of the LO mixing with the fundamental of the BFO. In my K2 I
found evidence that the mixing was taking place in the first mixer, the
TUF-1 diode ring.

Using whole numbers and assuming that the IF is 4914 kHz, therefore the
BFO's fundamental is 4914 kHz, when the receiver is tuned to 3589 kHz the
fundamental frequency of the LO will be 3589 + 4914 kHz, i.e. 8503 kHz.
Should the BFO and LO fundamentals mix, one product will be at 8503 - 4914
kHz, i.e. at 3589 kHz.

There is, unfortunately, no simple fix to this problem as far as I know,
because due to the lack of shielding and lead filtering the fundamentals and
harmonics of all the oscillators in the K2 can be found in places where they
should not be inside the K2, which results in its birdie problem.

Although a receiver spurious response is not involved in this particular
case, and all superhet receivers have spurious responses to a greater or
lesser extent, if a mixing product generated by two or more internal
oscillators should be "heard" by a receiver's spurious response, then this
would result in a birdie. In the majority of cases it is the lower order
harmonics of the oscillators which create birdie problems.

73,
Geoff
GM4ESD

John VK7JB wrote on Tuesday, November 02, 2010, at 11:50 AM:

> Hi All,
>
> I've just finished K2/100 #6998. After blowing the PA transistors of the
> base K2 by accidentally dropping the frequency probe into the works, I've
> completed the KPA100, installed it and all is working very well. Made
> several SSB contacts tonight and I couldn't be happier. I have a great
> sense of achievement :)
>
> I'm curious about a prominent birdie, zero beat at 3589khz. It's present,
> and more prominent, with the antenna disconnected and has its origin
> internally.
>
> There are some postings about this birdie from around 2008, but I don't
> see
> any resolution. I can live with it, even though it's inconveniently
> located
> right where I like to work on SSB phone. Did anyone work out where this
> comes from and whether or not there is a simple fix?
>
> Also, I've calibrated the K2 reference oscillator several times according
> to
> the N6KR method. The result is that my frequency display is 20hz off
> frequency after the rig has warmed up: eg it reads 9999.98 for 10000.00
> WWV
> signal. Am I correct in understanding this is about as good I can expect
> given the DAC parameters of the K2? I can't seem to improve on it further
> by repeating it.
>
> 73,
>
> John
> VK7JB