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K1: Band 2 (15M) low audio and a steady tone on one frequency

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MGFoster

K1: Band 2 (15M) low audio and a steady tone on one frequency

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Greetings,

I have the 2 band (40M/15M) filter board, and the 15M receiver has very
poor reception and a very loud, steady tone on one frequency. The
tone's bandwith is very narrow (about 2 Hz). As soon as I construct the
RF probe I'll do some tests to determine why the reception is so poor.

I discovered this while installing the KAT1, which means I've installed
the connector at J2, thus removing the J2 jumper. I was wondering if I
can temporarily insert a scrap component lead as a jumper in the
connector rather than destroy the connector to remove it & re-install
the jumper (while I test the Band 2 set-up without the KAT1)?

Also, has anyone any idea what may be the cause of the steady tone? I
didn't see any mention in the list archive of a similar occurrence. My
initial hunch is that it is a symptom of a short, possibly in the
crystal.

Thanks,
--
MGFoster:::mgf00 <at> earthlink <decimal-point> net
Oakland, CA (USA)

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Brett Howard

Re: K1: Band 2 (15M) low audio and a steady tone on one frequency

You should be fine to install a jumper. My K1 actually gives you the
connector and has you install a jumper with standard insulated solid
core wire which is to be removed if you buy the KAT1 option (which I
did). Installing a wire like this is no different than the single
"turn" that you did on the only transformer that you wound when you
built the KAT1. This transformer is what allows it to take the forward
and reflected power measurements.

Wish you the best of luck finding the cause of your birdie.

On Sun, 2008-01-20 at 04:51 -0800, MGFoster wrote:

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>
> Greetings,
>
> I have the 2 band (40M/15M) filter board, and the 15M receiver has very
> poor reception and a very loud, steady tone on one frequency. The
> tone's bandwith is very narrow (about 2 Hz). As soon as I construct the
> RF probe I'll do some tests to determine why the reception is so poor.
>
> I discovered this while installing the KAT1, which means I've installed
> the connector at J2, thus removing the J2 jumper. I was wondering if I
> can temporarily insert a scrap component lead as a jumper in the
> connector rather than destroy the connector to remove it & re-install
> the jumper (while I test the Band 2 set-up without the KAT1)?
>
> Also, has anyone any idea what may be the cause of the steady tone? I
> didn't see any mention in the list archive of a similar occurrence. My
> initial hunch is that it is a symptom of a short, possibly in the
> crystal.
>
> Thanks,

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Don Wilhelm-4

Re: K1: Band 2 (15M) low audio and a steady tone on one frequency

In reply to this post by MGFoster

Yes, you can use a wire jumper - just bend a component lead and stick
its ends into the socket.
The best first step is to see if you can hear the crystal frequency in a
general coverage receiver. Connect a length of wire to the receiver
antenna jack center conductor and use it as a probe near the K1 crystal.

73,
Don W3FPR

MGFoster wrote:

Mike Morrow-3

Re: K1: Band 2 (15M) low audio and a steady tone on one frequency

In reply to this post by MGFoster

>... the 15M receiver has very poor reception and a very loud,
> steady tone on one frequency. The tone's bandwith is very narrow...
>
>...has anyone any idea what may be the cause of the steady tone?
>...initial hunch is that it is a symptom of a short, possibly in the
>crystal.

It would help if you state at what indicated frequency you hear the tone. Anyway, **ignore** your hunch in this case.

No doubt you are hearing the seventh harmonic ("birdie") of the K1's VFO on 15m. This frequency varies from unit to unit. On my K1 it occurs near 21072 kHz, where my K1's VFO is just above 3010 kHz. The tuning seems very sharp because as one tunes upward, the VFO frequency goes downward, which makes the reception of the VFO's seventh harmonic appear vary narrow as one tunes across it. The receiver frequency is changing in one direction, while the received VFO signal frequency is changing in the opposite direction. Thus, very "sharp" birdies are a dead give-away of reception of an internal VFO harmonic on the K1.

This harmonic near 21072 kHz is the worst case of a birdie that will be be found on any of the K1's official bands (80m to 15m). Its actual frequency will vary a little from one K1 to another due to variations in the frequencies of the product detector and filter board heterodyne crystals. The birdie will seem very strong if your receiver is working but you have no antenna connected, or the antenna signal isn't making it to the receiver front end. Since it seems so loud on your set, that could indicate that the receiver is working fine (and picking up this harmonic), but you've lost connection to the external world (antenna) which normally provides noise and signals to compete with the harmonic. Beware...sometimes, a very dead 15m band will almost duplicate the effect of an antenna disconnection.

What can be done about the birdie? Not much. Fortunately, most 15m activity is below the birdie, the birdie is narrow, and an open band with signals will diminish its perceived effect.

Mike / KK5F
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MGFoster

Re: K1: Band 2 (15M) low audio and a steady tone on one frequency

In reply to this post by MGFoster

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Mike Morrow wrote:
> No doubt you are hearing the seventh harmonic ("birdie") of the K1's
> VFO on 15m. This frequency varies from unit to unit. On my K1 it
> occurs near 21072 kHz,

You're correct, the tone is on 21072 kHz.

I've been testing the rcvr at night, which, duh, obviously will produce
weak signals on 15M. Today I compared the K1 rcvr to a general coverage
rcvr on 21 MHz and both rcvrs gave the approximate same signal
strengths. So, no problems.

Thanks for your help.
--
MGFoster:::mgf00 <at> earthlink <decimal-point> net
Oakland, CA (USA)

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--
MGFoster:::mgf00 <at> earthlink <decimal-point> net
Oakland, CA (USA)
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