KX3 IQ Outputs - What to expect?

[John Huggins, kx4o]

Hello all,

I'm trying to debug something here and need help with some concepts.

Has anyone ever looked at the I and Q outputs of a KX3 with a 2 channel
o-scope while tuning above and below a fixed carrier - from a test
source perhaps?

If so can you comment on the relative amplitudes and phase difference
observed vs. the tuning offset from the test signal?

Thanks.

John, kx4o
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[Peter Lambert]

Hi John,

In this situation the amplitude of both the I and Q channels should be the
same and they should always be 90 degrees out of phase.

Peter VK4JD

-----Original Message-----
From: Elecraft [mailto:[hidden email]] On Behalf Of John
Sent: Tuesday, 17 March 2015 8:49 AM
To: [hidden email]
Subject: [Elecraft] KX3 IQ Outputs - What to expect?

Hello all,

I'm trying to debug something here and need help with some concepts.

Has anyone ever looked at the I and Q outputs of a KX3 with a 2 channel
o-scope while tuning above and below a fixed carrier - from a test source
perhaps?

If so can you comment on the relative amplitudes and phase difference
observed vs. the tuning offset from the test signal?

Thanks.

John, kx4o
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[John Huggins, kx4o]

Thanks Peter.

I do see the 90 degree phase difference and how it changes if I move
above or below the test frequency.  However the amplitude of just one,
the ring conductor on the connector, decreases with increasing delta
frequency.  The amplitude of the tip remains steady regardless of the
delta frequency.

I assume this isn't what I should be seeing.  Now I need to figure out
me next move as this seems to not be what the PX3 wants.

Does anyone know a reason the I and Q might be different amplitudes for
the same signal?

Thanks.
John, kx4o

On 3/16/2015 8:38 PM, Peter Lambert wrote:
> Hi John,
>
> In this situation the amplitude of both the I and Q channels should be the
> same and they should always be 90 degrees out of phase.
>
> Peter VK4JD
>
>

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[Peter Lambert]

Hello again John,

Looking at the schematic, any difference you see should be so slight that
you'd not make comment on it.  If it were me I'd take a look at the
inductors LD-LG (on page 4 of the schematic) to see if there is the
possibility of one of them being shorted.  I haven't had look at these but
it's common to twist the terminating wires together - a likely spot for a
short.

I'd stick the CRO on the output of each of the 4 inductors (where the
circuit shows "RX_I" and "RX_Q" and the opposite side of C1K and C1L) all
the levels here should be pretty much identical.

Of course you can only expect this over the range of +- 96kHz or so.

73's Peter VK4JD

PS - love this little radio, it's an amazing bit of portable kit

-----Original Message-----
From: John [mailto:[hidden email]]
Sent: Tuesday, 17 March 2015 1:53 PM
To: Peter Lambert; [hidden email]
Subject: Re: [Elecraft] KX3 IQ Outputs - What to expect?

Thanks Peter.

I do see the 90 degree phase difference and how it changes if I move above
or below the test frequency.  However the amplitude of just one, the ring
conductor on the connector, decreases with increasing delta frequency.  The
amplitude of the tip remains steady regardless of the delta frequency.

I assume this isn't what I should be seeing.  Now I need to figure out me
next move as this seems to not be what the PX3 wants.

Does anyone know a reason the I and Q might be different amplitudes for the
same signal?

Thanks.
John, kx4o

On 3/16/2015 8:38 PM, Peter Lambert wrote:
> Hi John,
>
> In this situation the amplitude of both the I and Q channels should be
> the same and they should always be 90 degrees out of phase.
>
> Peter VK4JD
>
>

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[John Huggins, kx4o]

On Tue, March 17, 2015 05:16, Peter Lambert wrote:
Thanks Peter.  Good clues and I will have a look.  Schematics printed and
heading to work where we maintain an electronics lab that is an
anti-static wonderland.

I wonder, though, if there isn't some external forensics to try first.  I
mean if the I or Q are not proper at the points you mention, there should
be some evidence in the operation right?  Although I do note proper I an Q
levels when the VFO is close to the test frequency and within the
demodulating bandwidth.

Elecraft has been sent a note along with o-scope plots of the IQ out
connector, but I will perform a visual inspection of the spots you
mention.

John

> Hello again John,
>
>
> Looking at the schematic, any difference you see should be so slight that
>  you'd not make comment on it.  If it were me I'd take a look at the
> inductors LD-LG (on page 4 of the schematic) to see if there is the
> possibility of one of them being shorted.  I haven't had look at these
> but it's common to twist the terminating wires together - a likely spot
> for a short.
>
> I'd stick the CRO on the output of each of the 4 inductors (where the
> circuit shows "RX_I" and "RX_Q" and the opposite side of C1K and C1L) all
> the levels here should be pretty much identical.
>
> Of course you can only expect this over the range of +- 96kHz or so.
>
>
> 73's Peter VK4JD
>
>

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