Birdies

[OE5CSP-Chris]

Hello group,

I´m the owner of a K2,which I bought last week from a fellow ham and at the
moment I´m testing and studying how to operate this rig.
The number of my K2 is 02447. Maybe my question has been asked a lot of
times, but I`d be glad to get an answer:
My rig seems to have quite a few birdies(I hope this is the right expression
in English-like a whistle, in German “Pfeifton”)
I called the previous owner of the K2 and asked him about the birdies.He
turned on his K2(he has a second one) and he also found them-not all of
them,but quite a few.
Sometimes, when I connect the antenna again the birdies are gone, sometimes
changing the filters helps, but they quite often stay.
So, what have I done wrong or what has the previous owner done wrong? Is it
just an operating mistake? I´m using analog filters and on 14012.07,
28004.4, 18068.7 and many other frequencies on the ham bands I can find
them.The op, who built the rig can´t help me, he says it´s not his fault…so,
who can help me.Any comments welcome!

                                      Vy 73 Chris-OE5CSP

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[S55M]

Hello Chris!

I think that birdies are normal behavior of K2 (nonexisting shielding inside
K2 between different modules).
Some of them can be resolved , some of them will stay but You can live with
them and still have nice rig.
When You'll attach the antenna almost all birdies will be coverd by antenna
noise...
It also depends of Your configuration of K2. If You have 100W amp or not,
KIO2 or not ecc...

And for most of the birdies there is no simple solution :(

73's

S55M-Adi

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[Vic K2VCO]

Hans-Christoph Scheiblberger wrote:

> My rig seems to have quite a few birdies

I have been struggling with them for some time, and have had the able
help of Geoff, GM4ESD, who has done various experiments and analyses.

The worst ones seem to be related to the bias oscillator in the KPA100
(note that this oscillator runs at all times when the KPA100 is
installed, whether or not the power is over 10 watts).  The oscillator
crystal was originally 16.xxx MHz and in newer KPA100s or those with the
mod kit installed, 18.xxx MHz.  The birdies are the result of harmonics
of the oscillator mixing with harmonics of other oscillators in the K2.
  For example, I have one at 28.018 Mhz which results from (5 x 23.105)
- (6 x 18.434) = 4.9 Mhz. approximately.   The 18.434 is the bias
oscillator and the 23.105 Mhz is the VCO when the K2 is tuned to 28.018.

Note that the mixing takes place at VHF, so it's quite hard to get a
good ground point for bypassing and shielding purposes.  Some of the
following may help a little with some birdies:

1) Adding additional filtering to the output of the bias oscillator,
where it feeds the pin diode switch and where it goes to the RS232 chip.
   I used 10 uh chokes and 0.001 uf capacitors.

2) Putting a the ribbon cable from the amplifier through a ferrite toroid.

3) Replacing the traces that carry the speaker lines across the KPA
board with a length of RG/174 coax that is grounded only at the K2 RF board.

I was able to reduce my 28 MHz birdie from S7/S8 to S2/S3.  Still loud
enough to hear quite well with the antenna on.

I went so far as to install a shield over the top of the K2 RF board.
It didn't seem to help with the 28 MHz birdie.  You can see it as well
as the toroid on the ribbon cable and the coax to the speaker at
<http://www.qsl.net/k2vco/k2shield.jpg>.  I left it in place because who
knows what other spurs it may reduce!

--
73,
Vic, K2VCO
Fresno CA
http://www.qsl.net/k2vco
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