Elecraft] K3 K144XV spurious signal on 144,414.1

[Dave-3]

Its also by far the loudest sprog I can hear on the 3 K3/K144XV combos I
have tested. Unfortunately for me it stops me hearing the PI7RTD and ON0VHF
beacons 400km away unless they drift to a frequency that I can use my 250Hz
filter to dig them out

Dave
G4FRE

From: "Sverre Holm (LA3ZA)" <[hidden email]>
To: [hidden email]
Subject: [Elecraft] K3 K144XV spurious signal on 144,414.1
Message-ID: <[hidden email]>
Content-Type: text/plain; charset=us-ascii

I would appreciate it if other owners of the K3-K144XV would check for this
signal.

It appears as if it is a regular input signal, i. e. it tunes normally. But
it is still there even if the 2m antenna is disconnected or the input is
shorted, so it seems to be internally generated.

I have tried all the tricks I know such as moving of internal cables in the
K3. I also updated the K144XV firmware and that got rid of the spur at the
36th harmonic of the 4 MHZ K144XV processor crystal at 144,005.

But the 144,414.1 spur remains, close to the SK4MPI beacon at 144,412 which
is one of the main indicators of propagation here.

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[gm3sek]

Since I am trying to decide whether to buy another K3 for the 2m
station, this is all very timely.

Probing around using a very small insulated pickup loop and a completely
separate 2m receiver, the 144.416MHz signal is definitely not a spurious
response of the K3's receiver. It is a real carrier and it's coming from
the region of the DSP board(s) behind the front panel.

The frequency seems to be completely independent of the K3's main
tuning, band or mode,  and on my particular K3 the frequency is
144.4162MHz (zero-beating on a GPS-locked receiver).

The signal is quite loud with the probe loop held anywhere close to the
DSP board along its whole length and on either side. The signal is
louder when the loop is anywhere close to the main voltage regulator,
the board interconnects or one of the mounting pillars; and when the
probe is directly above or below U17 (EPM240TQFP100) it's S9+. All this
suggests quite a strong discrete signal source that doesn't have
sufficient local decoupling, so it is escaping via the supply rails and
probably creating circulating currents in the groundplane and metalwork.

The frequency is somehow being generated from the 14.7456MHz DSP clock
crystal Y1 (as can be heard by probing very close to the board, which
detunes the frequency). That isn't a precision oscillator, which
probably accounts for any small differences in the reported frequency.

However, there is no obvious harmonic relationship between 14.7456 and
144.416 (the factor between them is 9.79).

That's as much probing between expensive circuit boards as I'm willing
to risk! Over to Wayne... sorry, this is a fine way to begin the Monday
morning after Visalia.


73 from Ian GM3SEK


>-----Original Message-----
>From: Elecraft [mailto:[hidden email]] On Behalf Of
>Dave
>Sent: 20 April 2015 16:13
>To: [hidden email]
>Subject: [Elecraft] Elecraft] K3 K144XV spurious signal on 144,414.1
>
>Its also by far the loudest sprog I can hear on the 3 K3/K144XV combos
I

>have tested. Unfortunately for me it stops me hearing the PI7RTD and
>ON0VHF
>beacons 400km away unless they drift to a frequency that I can use my
>250Hz
>filter to dig them out
>
>Dave
>G4FRE
>
>From: "Sverre Holm (LA3ZA)" <[hidden email]>
>To: [hidden email]
>Subject: [Elecraft] K3 K144XV spurious signal on 144,414.1
>Message-ID: <[hidden email]>
>Content-Type: text/plain; charset=us-ascii
>
>I would appreciate it if other owners of the K3-K144XV would check for

this
>signal.
>
>It appears as if it is a regular input signal, i. e. it tunes normally.
But
>it is still there even if the 2m antenna is disconnected or the input
is
>shorted, so it seems to be internally generated.
>
>I have tried all the tricks I know such as moving of internal cables in
the
>K3. I also updated the K144XV firmware and that got rid of the spur at
the

>36th harmonic of the 4 MHZ K144XV processor crystal at 144,005.
>
>But the 144,414.1 spur remains, close to the SK4MPI beacon at 144,412
>which
>is one of the main indicators of propagation here.
>
>______________________________________________________________
>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]

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[Sverre Holm (LA3ZA)]

Thanks, Ian, for your very thorough detective work. This is very interesting. The odd thing is that the frequency doesn't seem to compute easily from any of the known frequencies inside the K3:

- 14 645.6 kHz DSP clock
- 16 000 kHz PIC clock
-   8 230 kHz 2nd mixer crystal
- 49 380 kHz Reference frequency

but there may be more

gm3sek wrote

Probing around using a very small insulated pickup loop and a completely
separate 2m receiver, the 144.416MHz signal is definitely not a spurious
response of the K3's receiver. It is a real carrier and it's coming from
the region of the DSP board(s) behind the front panel.

The frequency seems to be completely independent of the K3's main
tuning, band or mode,  and on my particular K3 the frequency is
144.4162MHz (zero-beating on a GPS-locked receiver).

The signal is quite loud with the probe loop held anywhere close to the
DSP board along its whole length and on either side. The signal is
louder when the loop is anywhere close to the main voltage regulator,
the board interconnects or one of the mounting pillars; and when the
probe is directly above or below U17 (EPM240TQFP100) it's S9+. All this
suggests quite a strong discrete signal source that doesn't have
sufficient local decoupling, so it is escaping via the supply rails and
probably creating circulating currents in the groundplane and metalwork.

The frequency is somehow being generated from the 14.7456MHz DSP clock
crystal Y1 (as can be heard by probing very close to the board, which
detunes the frequency). That isn't a precision oscillator, which
probably accounts for any small differences in the reported frequency.

[Sverre Holm (LA3ZA)]

I have now checked with a local ham here who is very active on 2m DX-ing and who uses the K3.

He says he can hear the internally generated 2m signals from the K3 if he places a short antenna on top of the K3 connected to his IC-706 on 2m. He hears a strong signal at 144.418 MHz as well as many weak and a few strong signals between 144 and 144.5 MHz.

Interestingly he also says that if he uses an external antenna on either his IC-706 or his DB6NT 2m transverter which is in an enclosure and placed directly on top of the K3 he will not hear any of them.

With undesired signals like these, one can either look for the source and try to quiet it, or one can shield the receiver to prevent it from hearing them. The latter actually seems to work in this case.

But can the K144XV either be better shielded in its internal mounting, or perhaps be moved external to the K3 in a separate shielded enclosure?

[Joe Subich, W4TV-4]

> But can the K144XV either be better shielded in its internal
> mounting, or perhaps be moved external to the K3 in a separate
> shielded enclosure?

The external transverter (in a separate, shielded enclosure) is the
XV144 ...

73,

   ... Joe, W4TV


On 2015-04-22 4:21 PM, Sverre Holm (LA3ZA) wrote:

> I have now checked with a local ham here who is very active on 2m DX-ing and
> who uses the K3.
>
> He says he can hear the internally generated 2m signals from the K3 if he
> places a short antenna on top of the K3 connected to his IC-706 on 2m. He
> hears a strong signal at 144.418 MHz as well as many weak and a few strong
> signals between 144 and 144.5 MHz.
>
> Interestingly he also says that if he uses an external antenna on either his
> IC-706 or his DB6NT 2m transverter which is in an enclosure and placed
> directly on top of the K3 he will not hear any of them.
>
> With undesired signals like these, one can either look for the source and
> try to quiet it, or one can shield the receiver to prevent it from hearing
> them. The latter actually seems to work in this case.
>
> But can the K144XV either be better shielded in its internal mounting, or
> perhaps be moved external to the K3 in a separate shielded enclosure?
>
>
>
>
> -----
> Sverre, LA3ZA
>
> K2 #2198, K3 #3391,
> LA3ZA Blog: http://la3za.blogspot.com,
> LA3ZA Unofficial Guide to K2 modifications: http://la3za.blogspot.com/p/la3za-unofficial-guide-to-elecraft-k2.html
> --
> View this message in context: http://elecraft.365791.n2.nabble.com/Elecraft-K3-K144XV-spurious-signal-on-144-414-1-tp7601567p7601748.html
> Sent from the Elecraft mailing list archive at Nabble.com.
> ______________________________________________________________
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>

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[Sverre Holm (LA3ZA)]

Of course, the XV144 is the external transverter. What I had in mind were those who already have the K144XV and who find all these false carriers so annyoing that they are tempted to go to such a drastic measure as to move the transverter to the outside.

Joe Subich, W4TV-4 wrote

> But can the K144XV either be better shielded in its internal
> mounting, or perhaps be moved external to the K3 in a separate
> shielded enclosure?

The external transverter (in a separate, shielded enclosure) is the
XV144 ...

73,

   ... Joe, W4TV