FS: KX1 Built and Fully Loaded

[Tedd Wong]

KX1
KXB30
KXAT1
KXPD1

Purchased in Oct. 2005.  $365 shipped CONUS.  Paypal preferred.

Tedd K6OI
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[n2htt-2]

I finally got a chance to try my KX1 on 80m last night. I've had the new KXB3080 installed for several weeks and did the resistor/L3 power mods, but haven't actually gotten on the air before now.

Late yesterday, about 2330 EDT I heard a weak station at around 3720. Zeroed him in with the K6XX tuning indicator, and replied to his call. He pause for a bit, then resumed calling CQ. Okay, I don't always get a reply -- my antenna is definitely not optimal for 80m, a 40m horizontal loop at about 20 ft, tuned with an externa tuner.

I then tuned up the band a few hundred hertz, and to my surprise found the same station calling at 599!! I answered him on this frequency, and we had a brief QSO. My report was not that great, 479/QRN and it turned out he was quite local, only about 30 miles away. A textbook example of NVIS I suppose, given my antenna.

So what did I hear the first time? Could that have been some kind of image on the other sideband leaking through? Groundwave? (whatever that means...) This is sort of like low band crop circles.... ;-)

Anyway, the KXB3080 seems to be working fine, and I will check out the other bands over the next few days. The receiver in the KX1 seems better since I made the mods, but that could just be a result of better alignment than before.

73,
Mike

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[Ron D'Eau Claire-2]

Mike wrote:

Late yesterday, about 2330 EDT I heard a weak station at around 3720. Zeroed
him in with the K6XX tuning indicator, and replied to his call. He pause for
a bit, then resumed calling CQ. Okay, I don't always get a reply -- my
antenna is definitely not optimal for 80m, a 40m horizontal loop at about 20
ft, tuned with an externa tuner.

I then tuned up the band a few hundred hertz, and to my surprise found the
same station calling at 599!! I answered him on this frequency, and we had a
brief QSO. My report was not that great, 479/QRN and it turned out he was
quite local, only about 30 miles away. A textbook example of NVIS I suppose,
given my antenna.

So what did I hear the first time? Could that have been some kind of image
on the other sideband leaking through? Groundwave? (whatever that means...)
This is sort of like low band crop circles.... ;-)

Anyway, the KXB3080 seems to be working fine, and I will check out the other
bands over the next few days. The receiver in the KX1 seems better since I
made the mods, but that could just be a result of better alignment than
before.

--------------------------------------

Yes, you heard an "image". All superheterodyne receivers (like the KX1) that
use a BFO for CW/SSB reception have two of them because they have two
mixers: one at the input to convert the signal frequency to the intermediate
frequency (I.F.) and another at the detector to convert the I.F. to audio.

It works like this. When you inject a signal and a second local signal
(local oscillator or BFO) into a mixer, the mixer reproduces the signal at
its output on frequencies that are the sum and difference of the input
frequencies.

The KX1 uses an I.F of about 4913.6 kHz. All signals coming in at the
antenna are converted to this frequency, amplified, filtered and passed to
the detector which is a mixer. A 'beat frequency oscillator' (BFO) produces
a signal at 4913.0 kHz. That means the detector puts out two signals, the
sum of these two frequencies and the difference between these two
frequencies. The sum is a very high RF frequency - over 9 MHz. That's easily
filtered out. The difference frequency is what we're interested in: 600 Hz.
That's the audio frequency you hear in the phones.

Now suppose you tune slightly so the same signal produces an I.F. of 4912.4
kHz. That mixes with the 4913.0 BFO to produce 600 Hz again! You'll hear the
same signal at two places on the "dial" separated by exactly twice the beat
frequency. In this case, they're 1200 Hz apart.

All superhets do this. In earlier receivers before modern crystal filters,
it was a very well understood phenomena. As the I.F. filters got better,
they would reject one of the signals. In this case, a high-performance
crystal filter (such as in the K2) would reduce the signal at the I.F. of
4912.4 so much you'd not likely hear it at all. Manufacturers called this
"single signal" reception: each signal now only appeared once as we tuned
across the bands. Amazing! <G>.

We've come to expect "single signal" reception in all modern gear these
days, but it depends entirely on how strong the signal is and how good the
I.F. filter is. The tiny filter used in the KX1 is not as good as the those
used in larger and more expensive rigs like the K2. Its "stop band"
attenuation isn't as good. That, coupled with your hearing a very strong
signal on the band, allowed you to hear that "other" signal that's normally
suppressed.

Even with the simple filter used in the KX1 you should only be able to hear
the second signal when listening to a very strong station!

Ron AC7AC


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[Mike Scott-7]

One way to determine if you are listening to an image is to note how the
signal tunes. On 40M and 80M the pitch of the signal should increase as you
turn the KX1 tuning knob clockwise (higher frequency). If the tone decreases
instead it is not being listened to on the proper side and you should tune
higher yet in frequency past zero beat to find the real signal.

On 30M and 20M the effect is just the opposite of the above description; the
proper signal will be on the lower side. (For the experienced ops, why is
the upper sideband found by tuning to the lower side? I have wondered about
the reverese logic of upper and lower terms for a while).

As Ron noted you will only experience this on signals strong enough to be
heard through the attenuation of the crystal filter. I grew up without
single signal receive capability, in those days the signal sounded the same
on either side of zero beat. My first kit was the Heathkit HR10 receiver.

Mike Scott
AE6WA
Tarzana, CA (near LA)
Elecraft KX1 4-Watts


-----Original Message-----
From: [hidden email]
[mailto:[hidden email]] On Behalf Of Ron D'Eau Claire
Sent: Wednesday, May 24, 2006 11:38 AM
To: [hidden email]; [hidden email]
Subject: RE: [Elecraft] First 80m QSO w/KXB3080 a little odd...

Mike wrote:

Late yesterday, about 2330 EDT I heard a weak station at around 3720. Zeroed
him in with the K6XX tuning indicator, and replied to his call. He pause for
a bit, then resumed calling CQ. Okay, I don't always get a reply -- my
antenna is definitely not optimal for 80m, a 40m horizontal loop at about 20
ft, tuned with an externa tuner.

I then tuned up the band a few hundred hertz, and to my surprise found the
same station calling at 599!! I answered him on this frequency, and we had a
brief QSO. My report was not that great, 479/QRN and it turned out he was
quite local, only about 30 miles away. A textbook example of NVIS I suppose,
given my antenna.

So what did I hear the first time? Could that have been some kind of image
on the other sideband leaking through? Groundwave? (whatever that means...)
This is sort of like low band crop circles.... ;-)

Anyway, the KXB3080 seems to be working fine, and I will check out the other
bands over the next few days. The receiver in the KX1 seems better since I
made the mods, but that could just be a result of better alignment than
before.

--------------------------------------

Yes, you heard an "image". All superheterodyne receivers (like the KX1) that
use a BFO for CW/SSB reception have two of them because they have two
mixers: one at the input to convert the signal frequency to the intermediate
frequency (I.F.) and another at the detector to convert the I.F. to audio.

It works like this. When you inject a signal and a second local signal
(local oscillator or BFO) into a mixer, the mixer reproduces the signal at
its output on frequencies that are the sum and difference of the input
frequencies.

The KX1 uses an I.F of about 4913.6 kHz. All signals coming in at the
antenna are converted to this frequency, amplified, filtered and passed to
the detector which is a mixer. A 'beat frequency oscillator' (BFO) produces
a signal at 4913.0 kHz. That means the detector puts out two signals, the
sum of these two frequencies and the difference between these two
frequencies. The sum is a very high RF frequency - over 9 MHz. That's easily
filtered out. The difference frequency is what we're interested in: 600 Hz.
That's the audio frequency you hear in the phones.

Now suppose you tune slightly so the same signal produces an I.F. of 4912.4
kHz. That mixes with the 4913.0 BFO to produce 600 Hz again! You'll hear the
same signal at two places on the "dial" separated by exactly twice the beat
frequency. In this case, they're 1200 Hz apart.

All superhets do this. In earlier receivers before modern crystal filters,
it was a very well understood phenomena. As the I.F. filters got better,
they would reject one of the signals. In this case, a high-performance
crystal filter (such as in the K2) would reduce the signal at the I.F. of
4912.4 so much you'd not likely hear it at all. Manufacturers called this
"single signal" reception: each signal now only appeared once as we tuned
across the bands. Amazing! <G>.

We've come to expect "single signal" reception in all modern gear these
days, but it depends entirely on how strong the signal is and how good the
I.F. filter is. The tiny filter used in the KX1 is not as good as the those
used in larger and more expensive rigs like the K2. Its "stop band"
attenuation isn't as good. That, coupled with your hearing a very strong
signal on the band, allowed you to hear that "other" signal that's normally
suppressed.

Even with the simple filter used in the KX1 you should only be able to hear
the second signal when listening to a very strong station!

Ron AC7AC


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[n2htt-2]

Thanks to Ron for his excellent explanation and all the others who replied. Now that I know about the 1200 hz difference I will keep an ear out for this phenomenon.

Do you think this would happen in the K1 also, or are the K1 filters sharper?

I'm much more used to hearing very weak signals rather than very strong ones -- after all I did answer the supressed image first :-)

73,
Mike N2HTT

> Yes, you heard an "image". All superheterodyne receivers (like the
> KX1) that
> use a BFO for CW/SSB reception have two of them because they have two
> mixers: one at the input to convert the signal frequency to the
> intermediatefrequency (I.F.) and another at the detector to convert
> the I.F. to audio.
>
> It works like this. When you inject a signal and a second local signal
> (local oscillator or BFO) into a mixer, the mixer reproduces the
> signal at
> its output on frequencies that are the sum and difference of the input
> frequencies.
>
> The KX1 uses an I.F of about 4913.6 kHz. All signals coming in at the
> antenna are converted to this frequency, amplified, filtered and
> passed to
> the detector which is a mixer. A 'beat frequency oscillator' (BFO)
> producesa signal at 4913.0 kHz. That means the detector puts out
> two signals, the
> sum of these two frequencies and the difference between these two
> frequencies. The sum is a very high RF frequency - over 9 MHz.
> That's easily
> filtered out. The difference frequency is what we're interested in:
> 600 Hz.
> That's the audio frequency you hear in the phones.
>
> Now suppose you tune slightly so the same signal produces an I.F.
> of 4912.4
> kHz. That mixes with the 4913.0 BFO to produce 600 Hz again! You'll
> hear the
> same signal at two places on the "dial" separated by exactly twice
> the beat
> frequency. In this case, they're 1200 Hz apart.
>
> All superhets do this. In earlier receivers before modern crystal
> filters,it was a very well understood phenomena. As the I.F.
> filters got better,
> they would reject one of the signals. In this case, a high-performance
> crystal filter (such as in the K2) would reduce the signal at the
> I.F. of
> 4912.4 so much you'd not likely hear it at all. Manufacturers
> called this
> "single signal" reception: each signal now only appeared once as we
> tunedacross the bands. Amazing! <G>.
>
> We've come to expect "single signal" reception in all modern gear
> thesedays, but it depends entirely on how strong the signal is and
> how good the
> I.F. filter is. The tiny filter used in the KX1 is not as good as
> the those
> used in larger and more expensive rigs like the K2. Its "stop band"
> attenuation isn't as good. That, coupled with your hearing a very
> strongsignal on the band, allowed you to hear that "other" signal
> that's normally
> suppressed.
>
> Even with the simple filter used in the KX1 you should only be able
> to hear
> the second signal when listening to a very strong station!
>
> Ron AC7AC
>
>
> _______________________________________________
> Elecraft mailing list
> Post to: [hidden email]
> You must be a subscriber to post to the list.
> Subscriber Info (Addr. Change, sub, unsub etc.):
> http://mailman.qth.net/mailman/listinfo/elecraft
>
> Help: http://mailman.qth.net/subscribers.htm
> Elecraft web page: http://www.elecraft.com
>

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