Elecraft › [K2]

K2 audio images strong signals 40 meters

Classic

List

Threaded

6 messages Options

paulb

K2 audio images strong signals 40 meters

Hi folks

K2 here has what appears to be an odd issue with strongs sigs
around 7175Khz

Tuning approx 5 Khz higher the same signal can be heard several s-points down.

Best guess seems to be centred around the 7175 - 7180 range.

I have a distant memory reading about this many years ago at build,
it's been a while..

thanks

cheers

Paul b
zl1aly

Don Wilhelm-4

Re: K2 audio images strong signals 40 meters

Paul,

Additional detail please - I don't have an immediate answer, but there
are a few possibilities.
The K2 serial number? If less than 3000, has it been upgraded with the
A to B mods?
What type of signal? CW or SSB?
Which IF filters are being used - width and sideband?
Has this been a problem since it was built?

Take a look at the K2 application note at
http://www.elecraft.com/Apps/Alert11_WAOF.html and see if that describes
the problem.

Since you are posting from Nabble, please copy a 'snippit' of what you
are referring to in your replies so those of us on the Elecraft
reflector have a reference. (The Elecraft reflector is not threaded).

73,
Don W3FPR

On 8/6/2014 3:55 AM, paulb wrote:

______________________________________________________________
Elecraft mailing list
Home: http://mailman.qth.net/mailman/listinfo/elecraft
Help: http://mailman.qth.net/mmfaq.htm
Post: mailto:[hidden email]

This list hosted by: http://www.qsl.net
Please help support this email list: http://www.qsl.net/donate.html
Message delivered to [hidden email]

Phil Wheeler-2

Re: K2 audio images strong signals 40 meters

In reply to this post by paulb

Go to Elecraft site and download the A-to-B update
instructions. As I recall this issue is discussed
early in that collection. I tested my K2 (#380)
earlier this year and it was OK in that regard.

Look in this document
http://www.elecraft.com/manual/k2a2binstr.pdf

Phil W7OX

On 8/6/14, 12:55 AM, paulb wrote:

> Hi folks
>
> K2 here has what appears to be an odd issue with strongs sigs
> around 7175Khz
>
> Tuning approx 5 Khz higher the same signal can be heard several s-points
> down.
>
> Best guess seems to be centred around the 7175 - 7180 range.
>
> I have a distant memory reading about this many years ago at build,
> it's been a while..
>
> thanks
>
> cheers
>
> Paul b
> zl1aly
>
>
>
>
> --
> View this message in context: http://elecraft.365791.n2.nabble.com/K2-audio-images-strong-signals-40-meters-tp7591965.html
> Sent from the Elecraft mailing list archive at Nabble.com.
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:[hidden email]
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
> Message delivered to [hidden email]
>

Don Wilhelm-4

Re: K2 audio images strong signals 40 meters

In reply to this post by paulb

Paul,

Just another thought on you issue.
Do you have the internal frequency counter probe inside your K2? If so,
remove it.
It should not be plugged in with the KPA100 installed in any case
because there is a possibility of spurious responses. I have never
heard of it causing a problem on receive, but yours could be the first
report.
If you do find it is the internal probe causing the problem, let all on
the reflector know about it, please.

73,
Don W3FPR

On 8/6/2014 3:55 AM, paulb wrote:

paulb

Re: K2 audio images strong signals 40 meters

In reply to this post by Don Wilhelm-4

Hi again folks

Update on K2 40 meter audio images around 7175;

Serial number of build is 6534 with most options installed.

Dummy load on Antenna RX 40 meters.

Test signals received on 7170 approx 50uVolt, S9 on the K2.

Tune to approx 7175 an image is heard. It is not inverted or
reversed tune.

Leave the K2 on 7170 and tune the test signal to 7184.
It can be heard on 7170.

Best approx guess is 5 s-points down so probably not
a big deal except when the band is quiet and strong signals
are nearby.

The calibration cable has been removed,

Filter setting and mode have no effect.
On CW the image signal tunes exactly the same, again
about 5 s-points down.

Noticed this oddity a while ago when listening to a couple of
strong SSB stations during daylight hours at another QTH
with low rf background noise.

Suspect this has been the same since build several years ago,
won't be loosing any sleep over it, more curious if it is
something related to vco mixing products somewhere?

I have noted the mods on earlier K2 builds, could well be
in the same field.

thanks for the replies

cheers

Paul b
zl1ajy

Don Wilhelm-4

Re: K2 audio images strong signals 40 meters

Paul,

Thanks for those details. I cannot attribute those offsets to anything
related to the BFO, but on 40 meters near 7185 kHz, the PLL and VCO
frequencies are quite close together, and interaction between the two
can cause some "strange happenings".

I believe you may be hearing some subset of the effects from the "Weird
At One Frequency" problem that was present in earlier K2s. Your K2 has
the 'fixes' that usually clear it up included in the above SN 3000 board
layout.
However, it is not entirely gone in *some* more recent K2s. Don't ask me
why, it varies from one K2 to another, I really don't have an answer -
it may have to do with construction practices and lead lengths above the
RF board, but that is just a guess.

As a first pass attack on the problem, use flush cutters and trim
everything in the vicinity of U4 so that nothing can act as a short
'antenna'.
Look at the leads for RFC15, C91 and C88 which are soldered to the pins
of U4 on the bottom of the board. They should be mounted to the pins of
U4 with the minimum lead length possible (the lead length on the side
away from U4 is not as critical).

If you have components (particularly capacitors and resistors and
varactors) with significant lead length above the board in the PLL and
VCO areas, reduce that lead length to the minimum possible and flush
trim the leads below the board.

Normal diagonal cutters will not cut sufficiently close to the board -
If you do not have them, buy, beg or borrow true Flush Cutters for this
task.

I can't promise that it will be a total cure, but it may reduce the
intensity of the responses.

73,
Don W3FPR

On 8/6/2014 7:20 PM, paulb wrote:

> Hi again folks
>
>
> Update on K2 40 meter audio images around 7175;
>
> Serial number of build is 6534 with most options installed.
>
> Dummy load on Antenna RX 40 meters.
>
> Test signals received on 7170 approx 50uVolt, S9 on the K2.
>
> Tune to approx 7175 an image is heard. It is not inverted or
> reversed tune.
>
> Leave the K2 on 7170 and tune the test signal to 7184.
> It can be heard on 7170.
>
> Best approx guess is 5 s-points down so probably not
> a big deal except when the band is quiet and strong signals
> are nearby.
>
> The calibration cable has been removed,
>
> Filter setting and mode have no effect.
> On CW the image signal tunes exactly the same, again
> about 5 s-points down.
>
> Noticed this oddity a while ago when listening to a couple of
> strong SSB stations during daylight hours at another QTH
> with low rf background noise.
>
> Suspect this has been the same since build several years ago,
> won't be loosing any sleep over it, more curious if it is
> something related to vco mixing products somewhere?
>
> I have noted the mods on earlier K2 builds, could well be
> in the same field.
>