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Re: I tried Support without a word in return -- so I'll try this

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Rick Beatty

Re: I tried Support without a word in return -- so I'll try this

Hi To the group -- this is my second time around, having 2 K2's -- as I
build the second one I have run into an issue that some of you might have
seen, or heard of.

All of the checks and tests required up to and including phase two (
receiver checkout) are nominal -- however, I find that the signal they ask
for you to check, at around 7.0Mhz is not there -- and signals off of an
antenna are also weak. I confirmed this by injecting a signal into the
antenna port and determined that the receiver is about a -70 to -75 db and
not the normal -100.

However, here is the kicker -- if I jumper from w2 to w3 the sensitivity
comes to normal and the 7.0Mhz signal is good and solid as well as signals
from the antenna.

What I want to know is what to do to fix it. This little test has me
thinking that that crystal filter is bad.

Comments please -- Rick NU7Z
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Eric Swartz - WA6HHQ

Re: I tried Support without a word in return -- so I'll try this

Administrator

Hi Rick,

Gary was out today - He should get back to you tomorrow.

Regards,
Eric WA6HHQ

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On 8/3/2011 5:14 PM, Rick Beatty wrote:

> Hi To the group -- this is my second time around, having 2 K2's -- as I
> build the second one I have run into an issue that some of you might have
> seen, or heard of.
>
> All of the checks and tests required up to and including phase two (
> receiver checkout) are nominal -- however, I find that the signal they ask
> for you to check, at around 7.0Mhz is not there -- and signals off of an
> antenna are also weak. I confirmed this by injecting a signal into the
> antenna port and determined that the receiver is about a -70 to -75 db and
> not the normal -100.
>
> However, here is the kicker -- if I jumper from w2 to w3 the sensitivity
> comes to normal and the 7.0Mhz signal is good and solid as well as signals
> from the antenna.
>
> What I want to know is what to do to fix it. This little test has me
> thinking that that crystal filter is bad.
>
> Comments please -- Rick NU7Z
>

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Don Wilhelm-4

Re: I tried Support without a word in return -- so I'll try this

In reply to this post by Rick Beatty

Rick,

While jumpering out the filter may increase the receiver response, there
are too many other things going on to make a solid judgement.

Receiver problems of that nature can be deceiving unless you do Signal
Tracing.

You apparently have a signal generator with a calibrated output, and I
suggest you turn to the Troubleshooting appendix in the back of the
manual and go through the Receiver Signal Tracing procedure. If you are
monitoring the RF voltage with an oscilloscope, multiply the expected
readings by 2.8 for the 'scope P-P RF voltage - if you have no 'scope,
now is a good time to build the RF probe from the parts supplied with
your K2 kit.

If I guessed wrong on your signal generator capability, you can build
the oscillator shown in the manual appendix - it works very well.

As Eric indicated, Gary has been gone, and he handles most of the K2
support issues.

73,
Don W3FPR

On 8/3/2011 8:14 PM, Rick Beatty wrote:

Mike K8CN

Re: I tried Support without a word in return -- so I'll try this

In reply to this post by Rick Beatty

Rick,

Presuming that you've already taken Don's customary advice (check all solder joints and re-heat anything that looks suspicious) in the vicinity of the 1st crystal filter, I would verify that one of the other crystals (X1 through X4) hasn't been inadvertently placed into one of the slots for X7 through X11 (the 1st variable bandwidth filter) or X5/X6 (the post-IF amp filter), and I would carefully check the varactors D29 through D34 to be sure they're the correct diodes.

If these checks don't reveal anything amiss, I would repeat the BFO Test and BFO Alignment (more often referred to as CAL FIL) from the Part II Alignment and Test procedures to be sure that your BFO tuning range and BFO frequency settings for the various filters FL1 through FL4 haven't effectively put the down-converted RF signal on the skirts of the 1st crystal filter's passband. Since you have an external RF signal source, you could use Spectrogram to check the position of a known input frequency at the antenna when it's mixed down to the audio range -- if you don't see the spike in the audio spectrum inside the filter's response passband, that's a good indication of the BFO frequency being incorrectly set. All of this presumes that you have an independent means (i.e., good external counter) to check the frequency of the RF input signal and that you observe a peak in the audio response when the K2 frequency display matches the RF input frequency (CW mode, not USB or LSB).

Don may have other suggestions based on his extensive knowledge of common K2 maladies.

73,
Mike, K8CN