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K2: AGC Threshold Too Low?

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Sarah K.

K2: AGC Threshold Too Low?

Hi,

I'm Sarah, AF6FH! I just got my license a couple weeks ago, and I'm
now assembling K2# 0622, which will be my first HF radio. I started
assembly on Wednesday night, and so far, everything's been going just
fine.

But...

I'm having a little issue with setting the AGC Threshold.

The instructions (pg. 48) say to set the RF GAIN control fully
clockwise, measure the voltage on pin 5 of U2 on the control board,
and adjust trimmer R1 for a reading of 3.80 volts.

I did my voltage measurements with my own (cheap) DMM, not the
internal voltmeter.

My concern is that, by adjusting R1, the highest I could get the
voltage to go was 3.59v, so for the moment, that's where it's set.

I measured the voltage on the LM29307-8, and it has 12.23V at the
input, but only 7.53V at the output. The 78M05 has 4.93V at its
output.

When I rotate the AF GAIN control, I get a range of 4.68V (fully
counter-clockwise) to 3.59V (fully clockwise) on pin 5 of U2.

My power supply is a small benchtop power supply; it's putting out
12.4V, and reports the K2 is drawing about 100mA. When I measure the
input voltage across the K2 input jack, I get the same 12.4V.

All of the previous checks were fine, and the following step, S-Meter
Alignment, seemed to work just fine.

So, my question is, do I have a problem? Should I be concerned?

Thanks,

Sarah AF6FH
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dave.wilburn

Re: K2: AGC Threshold Too Low?

Greetings Sarah, welcome to the hobby, and to a great radio. My AGC
measurement was down a bit, not quite as far as yours, but it has been
discussed here that there is some variation, and that it is not critical
at that point. I re-visited my a little later on in the build process,
and the numbers came up some.

Don, W3FPR, has given some good explanations for why this is, I just
don't recall them at the moment. A quick search of the archive;
http://www.mail-archive.com/elecraft@.../maillist.html

Here is one example of what I found;
http://www.mail-archive.com/elecraft@.../msg01791.html

So I don't think your measurement is at a critical level at this time.
Don, or others will likely help with further information. Best of luck
to you, and enjoy the build. It really is a fine radio. 73
-

David Wilburn
[hidden email]
K4DGW
K2 S/N 5982

On Fri, 2007-11-23 at 12:53 -0800, Sarah K. wrote:

> Hi,
>
> I'm Sarah, AF6FH! I just got my license a couple weeks ago, and I'm
> now assembling K2# 0622, which will be my first HF radio. I started
> assembly on Wednesday night, and so far, everything's been going just
> fine.
>
> But...
>
> I'm having a little issue with setting the AGC Threshold.
>
> The instructions (pg. 48) say to set the RF GAIN control fully
> clockwise, measure the voltage on pin 5 of U2 on the control board,
> and adjust trimmer R1 for a reading of 3.80 volts.
>
> I did my voltage measurements with my own (cheap) DMM, not the
> internal voltmeter.
>
> My concern is that, by adjusting R1, the highest I could get the
> voltage to go was 3.59v, so for the moment, that's where it's set.
>
> I measured the voltage on the LM29307-8, and it has 12.23V at the
> input, but only 7.53V at the output. The 78M05 has 4.93V at its
> output.
>
> When I rotate the AF GAIN control, I get a range of 4.68V (fully
> counter-clockwise) to 3.59V (fully clockwise) on pin 5 of U2.
>
> My power supply is a small benchtop power supply; it's putting out
> 12.4V, and reports the K2 is drawing about 100mA. When I measure the
> input voltage across the K2 input jack, I get the same 12.4V.
>
> All of the previous checks were fine, and the following step, S-Meter
> Alignment, seemed to work just fine.
>
> So, my question is, do I have a problem? Should I be concerned?
>
> Thanks,
>
> Sarah AF6FH
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>
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michael taylor-3

Re: K2: AGC Threshold Too Low?

In reply to this post by Sarah K.

On Nov 23, 2007 3:53 PM, Sarah K. <[hidden email]> wrote:
>
> I'm Sarah, AF6FH! I just got my license a couple weeks ago, and I'm
> now assembling K2# 0622, which will be my first HF radio. I started
> assembly on Wednesday night, and so far, everything's been going just
> fine.

Congrats, and welcome!

> I did my voltage measurements with my own (cheap) DMM, not the
> internal voltmeter.

Maybe a silly question, but is the DMM's batteries fresh? If it has
the half-dead cheap old batteries that it came with, the reading may
be off a bit too much.

A sanity check of comparing the measurement to ones done using the
internal voltmeter could help detect if that is the problem if you
don't have a fresh battery on hand.

> I measured the voltage on the LM29307-8, and it has 12.23V at the
> input, but only 7.53V at the output. The 78M05 has 4.93V at its
> output.

I would expect closer to 8V out of the LM2930T-8 but it is with spec
(7.5-8.5V from the LM2930 datasheet), and the input voltage is fine
(should only need 8.6 or 9V input to work correctly.

-Michael, VE3TIX
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Sarah K.

Re: K2: AGC Threshold Too Low?

In reply to this post by dave.wilburn

Thanks to everyone who replied! Wow, help sure comes in a hurry on
this list!

The general consensus appears to be that I'm ok for the time being
(yay!), so I'm going to go ahead and move on.

I did test with the internal voltmeter as well, and it reports 3.5V.

Special thanks to VE3TIX who asked if my DMM batteries are fresh...
no, they weren't! I replaced the battery and the display is a lot
easier to read now, thanks! Sadly, it still reports 3.59V.

Although I am starting to wonder about the general advisability of
relying on a meter that came free with my oscilloscope. :-)

Also, in the process of fiddling with things, I discovered that my
little bench power supply is very noisy! I was using my Yaesu VX-7R
as an ad-hoc RF probe; K4DGW sent me a link to a message from Don
Wilhelm in the list archives which got me thinking about noise, so I
grabbed the Yaesu to try to use as an RF probe, and discovered lots
of noise on 7MHz, 10MHz, and probably everywhere else (!), which went
away completely when I switched off the power supply! I rigged a
bunch of D batteries for 12V and powered the K2 with that instead; it
worked fine, the noise went away, but the AGC reading still wouldn't
go over 3.59v.

But I think I'm going to need a power supply... any recommendations?
I can probably try to stop by HRO tomorrow.

Oh, and if anyone has a recommendation for a high quality but fairly
inexpensive DMM, I'd be interested to hear about that too...

Thanks again everyone,

Sarah AF6FH

> On Fri, 2007-11-23 at 12:53 -0800, Sarah K. wrote:
>> Hi,
>>
>> I'm Sarah, AF6FH! I just got my license a couple weeks ago, and I'm
>> now assembling K2# 0622, which will be my first HF radio. I started
>> assembly on Wednesday night, and so far, everything's been going just
>> fine.
>>
>> But...
>>
>> I'm having a little issue with setting the AGC Threshold.
>>
>> The instructions (pg. 48) say to set the RF GAIN control fully
>> clockwise, measure the voltage on pin 5 of U2 on the control board,
>> and adjust trimmer R1 for a reading of 3.80 volts.
>>
>> I did my voltage measurements with my own (cheap) DMM, not the
>> internal voltmeter.
>>
>> My concern is that, by adjusting R1, the highest I could get the
>> voltage to go was 3.59v, so for the moment, that's where it's set.
>>
>> I measured the voltage on the LM29307-8, and it has 12.23V at the
>> input, but only 7.53V at the output. The 78M05 has 4.93V at its
>> output.
>>
>> When I rotate the AF GAIN control, I get a range of 4.68V (fully
>> counter-clockwise) to 3.59V (fully clockwise) on pin 5 of U2.
>>
>> My power supply is a small benchtop power supply; it's putting out
>> 12.4V, and reports the K2 is drawing about 100mA. When I measure the
>> input voltage across the K2 input jack, I get the same 12.4V.
>>
>> All of the previous checks were fine, and the following step, S-Meter
>> Alignment, seemed to work just fine.
>>
>> So, my question is, do I have a problem? Should I be concerned?
>>
>> Thanks,
>>
>> Sarah AF6FH

Don Wilhelm-4

Re: K2: AGC Threshold Too Low?

In reply to this post by Sarah K.

Sarah,

Congratulations on getting your license and venturing to build your K2.

The AGC Threshold high limit is directly proportional to the 8 volt
regulator actual output - if you follow the circuit you will discover
that that voltage is really the result of a 3 legged resistive voltage
divider. With a full 8 volts out of the regulator, the typical highest
voltage is about 3.85 to 3.9 volts depending on the exact values of the
5% tolerance resistors. Since your 8 volt regulator is near the lower
edge of its tolerance range (actually a bit lower than it should be),
you can set R1 to its full limit and things should work fine.

I would recommend that you replace the regulator since a 5% tolerance
would produce an output between 7.60 and 8.40 volts.

73,
Don W3FPR

Sarah K. wrote:

Sarah K.

Re: K2: AGC Threshold Too Low?

In reply to this post by Sarah K.

Hi All,

> I'm Sarah, AF6FH! I just got my license a couple weeks ago, and I'm
> now assembling K2# 0622, which will be my first HF radio. I started
> assembly on Wednesday night, and so far, everything's been going just
> fine.

Just to clarify, that should be K2 #06322... and it took me *three*
tries to type it right, even with the sticker in front of me.

But I really *am* AF6FH... I just looked it up again to be sure! :-)

Sigh.

Sarah, AF6FH, afraid to type my serial number again, LOL!

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Sarah K.

Re: K2: AGC Threshold Too Low?

In reply to this post by Don Wilhelm-4

On Nov 23, 2007, at 3:31 PM, Don Wilhelm wrote:

> Sarah,
>
> Congratulations on getting your license and venturing to build your
> K2.

Thanks!

> The AGC Threshold high limit is directly proportional to the 8 volt
> regulator actual output - if you follow the circuit you will
> discover that that voltage is really the result of a 3 legged
> resistive voltage divider. With a full 8 volts out of the
> regulator, the typical highest voltage is about 3.85 to 3.9 volts
> depending on the exact values of the 5% tolerance resistors. Since
> your 8 volt regulator is near the lower edge of its tolerance range
> (actually a bit lower than it should be), you can set R1 to its
> full limit and things should work fine.
>
> I would recommend that you replace the regulator since a 5%
> tolerance would produce an output between 7.60 and 8.40 volts.

Thanks! I'll email [hidden email] and see if they'd like to
send me another one next week; I don't have one of those laying around.

In the meantime, I'm proceeding with the RF board, since it sounds
like it will work ok for the time being.

> 73,
> Don W3FPR

Thanks again!

Sarah AF6FH

> Sarah K. wrote:
>> Hi,
>>
>> I'm Sarah, AF6FH! I just got my license a couple weeks ago, and I'm
>> now assembling K2# 0622, which will be my first HF radio. I started
>> assembly on Wednesday night, and so far, everything's been going just
>> fine.
>>
>> But...
>>
>> I'm having a little issue with setting the AGC Threshold.
>>
>> The instructions (pg. 48) say to set the RF GAIN control fully
>> clockwise, measure the voltage on pin 5 of U2 on the control board,
>> and adjust trimmer R1 for a reading of 3.80 volts.
>>
>> I did my voltage measurements with my own (cheap) DMM, not the
>> internal voltmeter.
>>
>> My concern is that, by adjusting R1, the highest I could get the
>> voltage to go was 3.59v, so for the moment, that's where it's set.
>>
>> I measured the voltage on the LM29307-8, and it has 12.23V at the
>> input, but only 7.53V at the output. The 78M05 has 4.93V at its
>> output.
>>
>>

AC7AC

RE: K2: AGC Threshold Too Low?

In reply to this post by Sarah K.

CONTENTS DELETED

The author has deleted this message.

Sarah K.

Re: K2: AGC Threshold Too Low?

Well, I searched around a bit and found *another* cheap DMM, which
seels to be reading about 0.12 to 0.14 volts higher than the first
one. Now I don't know which one to believe! :-)

("Carry one watch, or three, but never two...")

Now I need to find my *other* other meter, the analog one I got when I
was nine years old, and see what it thinks...

Sarah AF6FH

On Nov 23, 2007 4:47 PM, Ron D'Eau Claire <[hidden email]> wrote:
> Hi and welcome!
>
> It doesn't happen too often, but have you checked the accuracy of your
> "cheap" DMM? If you don't have anything to compare it with, you can get an
> idea of its condition by measuring the voltage across a fresh alkaline
> battery. It should read about 1.57 and 1.58 VDC.
>
> Ron AC7AC
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Sarah K.

Re: K2: AGC Threshold Too Low?

On Nov 23, 2007, at 9:02 PM, Leigh L Klotz, Jr. wrote:

> Circuit Specialists has meters and they throw in a free gift for
> over $50. Or Fry's retail this weekend. B&K is an OK economy
> brand available at both places. The cheap analog meter might cause
> you problems down the road with sensitive components on the
> resistance scale, so keep it for analog peaking of small voltages.

Actually, my "cheap" analog meter did come from Circuit Specialists!
I got it free when I bought my oscilloscope.

Having now measured my bench power supply (not my precious K2!) with
just about everything I own that measures voltage, I'm inclined to
believe that the Circuit Specialists freebie DMM is telling the
truth; it matches the meter built into the bench power supply. My
other tiny pocket-size DMM measures about a tenth of a volt higher,
and my analog meter from when I was nine measures about a tenth of a
volt lower and hasn't been calibrated since about 1977.

So at the moment, I'm going to accept the freebie DMM's results...
unless somebody knows how many voltmeters it takes to establish a
quorum... :-)

But I'm still thinking that, sooner or later, it would be nice to
have a "nice" meter... so again, if anyone can recommend one that
isn't *too* expensive; I'd be interested to hear. Maybe a bench meter
rather than a handheld? $100 to $200ish? And maybe something from
Circuit Specialists, because, you know, if I spent more than $50 on
my meter, I could get another meter for free! Maybe that would would
constitute a quorum? :-)

Sarah

> Leigh/WA5ZNU
> On Fri, 23 Nov 2007 6:47 pm, Sarah K. wrote:
>> Well, I searched around a bit and found *another* cheap DMM, which
>> seels to be reading about 0.12 to 0.14 volts higher than the first
>> one. Now I don't know which one to believe! :-)
>>
>> ("Carry one watch, or three, but never two...")
>>
>> Now I need to find my *other* other meter, the analog one I got
>> when I
>> was nine years old, and see what it thinks...
>>
>> Sarah AF6FH
>>
>> On Nov 23, 2007 4:47 PM, Ron D'Eau Claire <[hidden email]> wrote:
>>> Hi and welcome!
>>>
>>> It doesn't happen too often, but have you checked the accuracy
>>> of your
>>> "cheap" DMM? If you don't have anything to compare it with, you
>>> can get an
>>> idea of its condition by measuring the voltage across a fresh
>>> alkaline
>>> battery. It should read about 1.57 and 1.58 VDC.
>>>
>>> Ron AC7AC

Sarah K.

AGC Threshold Ok! (was Re: K2: AGC Threshold Too Low?)

In reply to this post by Sarah K.

Hi All,

Good news... I got my K2's replacement voltage regulator (LM2930T-8)
from Elecraft on Friday. Today I took out the old one and put in the
new one... the output of the voltage regulator is now 8.04 volts,
which is a whole lot better than the 7.53 volts I had gotten before!
And after adjusting R1, the AGC threshold is reading 3.80, exactly
where it should be!

Elecraft also sent me a replacement R116 which was missing (I think!)
so I was able to finish building Part II and move on to the alignment
and test for Part II.

Someone on the list (NM5B) had recommend I pick up a few of the
Elecraft mini-modules, so I ordered the noise generator, the 50uV
signal generator, and the dummy load. I put those together today too,
with no issues, and used them to help work through the alignment and
test.

On the whole, I was quite happy with the results of the alignment and
test; all of the instructions were fairly straightforward, and, even
better, my K2 seemed to pass all of them perfectly! Yay!

And the noise generator works; I can hear the noise. The signal
generator works, too; when I tune around 7040 kHz, I can hear the 40m
50uV oscillator.

Now comes my strange and possibly embarrassing question...

Um... should I be able to receive anything yet? Keep in mind, this is
my first radio... well, second, if you count my Yaesu VX-7R... and I
don't entirely know what to expect.

I have what is probably a very bad antenna; it's just two pieces of
random wire I had laying around, soldered onto a BNC connector, and
draped around the room. The total length is probably 20-25 feet,
which I *know* isn't the right length for 40 meters... but it was the
longest wire I had laying around. When I hook it to the K2 via a 3ft
BNC patch cable, I definitely hear an increase in the noise level in
the headphones.

But I wasn't able to tune into anything that sounded like an actual
transmission. No voice, no CW. I tried switching between CW, LSB, and
USB. And I fiddled with the filter settings.

I did hear a couple different kinds of things:

I hear whistling noises that increase or decrease in pitch as I tune
around.

I hear "pops" that happen when I tune across some small range of
frequencies. These pops seem to be mostly repeatable, as if I'm
hitting something in the same spot in the band, but I was never able
to tune in to anything.

I do also hear several places where the noise is louder, and the S-
meter increases by a notch or two... and once or twice I heard
something that could possibly have been very, very garbled speech.
But I wasn't ever able to tune into those, either, and in fact it
could have been my imagination.

And, so far... that's about it.

Some other things that might be worth pointing out: I have a high-
voltage transmission line and a substation about a block away from
me... and my antenna is parallel to it. And I connected the VX-7R to
the same antenna and it gets similar kinds of noise, and no signals
on 40m either. Also, I'm on the 2nd floor of an apartment, and an
outside antenna isn't going to be feasible here. I didn't try
grounding the K2 to the electrical ground yet... I certainly can't
install my own ground rod, either! I was running the K2 from 12 volts
worth of D batteries, to minimize power supply noise. And I turned
off all the fluorescent lights, which dropped the noise considerably,
but didn't reveal anything underneath the noise.

So... does this sound appropriate given the current situation? Should
I be hearing more than this? Am I not understanding how the K2 works?
Am I missing something very basic about ham radio? Am I doing
something silly? :-)

Should I try a better/different antenna? I now have about 150ft of
12ga stranded wire that I can use for a second test antenna; if I
run it perpendicular to the high voltage line I think I can go 40ft
in a mostly straight line, and probably 50ft with one right-angle
bend in it. I can't get to 67ft without some major contortions; my
apartment just isn't that big! I have the internal antenna tuner for
my K2 but of course I haven't put it together yet!

Or could there be something wrong with my partly-assembled K2?

To date, I've heard almost nothing on *any* HF band... once or twice
I've been able to hear faint strains of music on the VX-7R, when
using the pre-programmed "Shortwave Broacast" built-in memory. And I
have another little transistor radio that has shortwave bands on
it... and I've never heard anything on that either. Could I somehow
be in a location where I can't receive much of anything? (I do hear
stuff on VHF bands with the VX-7R.)

Suggestions/recommendations welcome!

Thanks,

Sarah AF6FH

On Nov 23, 2007, at 12:53 PM, Sarah K. wrote: [quoted bit corrected
for typos!]

> Hi,
>
> I'm Sarah, AF6FH! I just got my license a couple weeks ago, and I'm
> now assembling K2# 06322, which will be my first HF radio. I started
> assembly on Wednesday night, and so far, everything's been going just
> fine.
>
> But...
>
> I'm having a little issue with setting the AGC Threshold.
>
> The instructions (pg. 48) say to set the RF GAIN control fully
> clockwise, measure the voltage on pin 5 of U2 on the control board,
> and adjust trimmer R1 for a reading of 3.80 volts.
>
> I did my voltage measurements with my own (cheap) DMM, not the
> internal voltmeter.
>
> My concern is that, by adjusting R1, the highest I could get the
> voltage to go was 3.59v, so for the moment, that's where it's set.
>
> I measured the voltage on the LM2930T-8, and it has 12.23V at the
> input, but only 7.53V at the output. The 78M05 has 4.93V at its
> output.
>
> When I rotate the AF GAIN control, I get a range of 4.68V (fully
> counter-clockwise) to 3.59V (fully clockwise) on pin 5 of U2.
>
> My power supply is a small benchtop power supply; it's putting out
> 12.4V, and reports the K2 is drawing about 100mA. When I measure the
> input voltage across the K2 input jack, I get the same 12.4V.
>
> All of the previous checks were fine, and the following step, S-Meter
> Alignment, seemed to work just fine.
>
> So, my question is, do I have a problem? Should I be concerned?
>
> Thanks,
>
> Sarah AF6FH

Kurt Pawlikowski

Re: AGC Threshold Ok! (was Re: K2: AGC Threshold Too Low?)

Sarah,

While I'm not familiar with the VX-7R and don't own a K2, it sounds
like things are working. If you receive something from the noise
generator and the signal generator (particularly if you switch the
latter to 1 micro-volt), your rig is probably working correctly. I don't
know how much that will change when you have completed the radio. I'm
told that in a properly adjusted (and complete?) radio, a 1 micro-volt
signal should register about S-3 and 50 micro-volt should be something
like 20 db over 9. Part of what you are experiencing is the relatively
poor HF band conditions and part is from the low gain antenna. If you
tune around during the day, you should probably hear *something* in at
least the 40 meter CW portion...

Hope that helps! Have fun.

Regards,

kurtt

Kurt Pawlikowski, AKA WB9FMC
The Pinrod Corporation
[hidden email]
(773) 284-9500
http://pinrod.com

Sarah K wrote:

> Hi All,
>
> Good news... I got my K2's replacement voltage regulator (LM2930T-8)
> from Elecraft on Friday. Today I took out the old one and put in the
> new one... the output of the voltage regulator is now 8.04 volts,
> which is a whole lot better than the 7.53 volts I had gotten before!
> And after adjusting R1, the AGC threshold is reading 3.80, exactly
> where it should be!
>
> Elecraft also sent me a replacement R116 which was missing (I think!)
> so I was able to finish building Part II and move on to the alignment
> and test for Part II.
>
> Someone on the list (NM5B) had recommend I pick up a few of the
> Elecraft mini-modules, so I ordered the noise generator, the 50uV
> signal generator, and the dummy load. I put those together today too,
> with no issues, and used them to help work through the alignment and
> test.
>
> On the whole, I was quite happy with the results of the alignment and
> test; all of the instructions were fairly straightforward, and, even
> better, my K2 seemed to pass all of them perfectly! Yay!
>
> And the noise generator works; I can hear the noise. The signal
> generator works, too; when I tune around 7040 kHz, I can hear the 40m
> 50uV oscillator.
>
> Now comes my strange and possibly embarrassing question...
>
> Um... should I be able to receive anything yet? Keep in mind, this is
> my first radio... well, second, if you count my Yaesu VX-7R... and I
> don't entirely know what to expect.
>
> I have what is probably a very bad antenna; it's just two pieces of
> random wire I had laying around, soldered onto a BNC connector, and
> draped around the room. The total length is probably 20-25 feet, which
> I *know* isn't the right length for 40 meters... but it was the
> longest wire I had laying around. When I hook it to the K2 via a 3ft
> BNC patch cable, I definitely hear an increase in the noise level in
> the headphones.
>
> But I wasn't able to tune into anything that sounded like an actual
> transmission. No voice, no CW. I tried switching between CW, LSB, and
> USB. And I fiddled with the filter settings.
>
> I did hear a couple different kinds of things:
>
> I hear whistling noises that increase or decrease in pitch as I tune
> around.
>
> I hear "pops" that happen when I tune across some small range of
> frequencies. These pops seem to be mostly repeatable, as if I'm
> hitting something in the same spot in the band, but I was never able
> to tune in to anything.
>
> I do also hear several places where the noise is louder, and the
> S-meter increases by a notch or two... and once or twice I heard
> something that could possibly have been very, very garbled speech. But
> I wasn't ever able to tune into those, either, and in fact it could
> have been my imagination.
>
> And, so far... that's about it.
>
> Some other things that might be worth pointing out: I have a
> high-voltage transmission line and a substation about a block away
> from me... and my antenna is parallel to it. And I connected the VX-7R
> to the same antenna and it gets similar kinds of noise, and no signals
> on 40m either. Also, I'm on the 2nd floor of an apartment, and an
> outside antenna isn't going to be feasible here. I didn't try
> grounding the K2 to the electrical ground yet... I certainly can't
> install my own ground rod, either! I was running the K2 from 12 volts
> worth of D batteries, to minimize power supply noise. And I turned off
> all the fluorescent lights, which dropped the noise considerably, but
> didn't reveal anything underneath the noise.
>
> So... does this sound appropriate given the current situation? Should
> I be hearing more than this? Am I not understanding how the K2 works?
> Am I missing something very basic about ham radio? Am I doing
> something silly? :-)
>
> Should I try a better/different antenna? I now have about 150ft of
> 12ga stranded wire that I can use for a second test antenna; if I run
> it perpendicular to the high voltage line I think I can go 40ft in a
> mostly straight line, and probably 50ft with one right-angle bend in
> it. I can't get to 67ft without some major contortions; my apartment
> just isn't that big! I have the internal antenna tuner for my K2 but
> of course I haven't put it together yet!
>
> Or could there be something wrong with my partly-assembled K2?
>
> To date, I've heard almost nothing on *any* HF band... once or twice
> I've been able to hear faint strains of music on the VX-7R, when using
> the pre-programmed "Shortwave Broacast" built-in memory. And I have
> another little transistor radio that has shortwave bands on it... and
> I've never heard anything on that either. Could I somehow be in a
> location where I can't receive much of anything? (I do hear stuff on
> VHF bands with the VX-7R.)
>
> Suggestions/recommendations welcome!
>
> Thanks,
>
> Sarah AF6FH
>
>
>
>
> On Nov 23, 2007, at 12:53 PM, Sarah K. wrote: [quoted bit corrected
> for typos!]
>> Hi,
>>
>> I'm Sarah, AF6FH! I just got my license a couple weeks ago, and I'm
>> now assembling K2# 06322, which will be my first HF radio. I started
>> assembly on Wednesday night, and so far, everything's been going just
>> fine.
>>
>> But...
>>
>> I'm having a little issue with setting the AGC Threshold.
>>
>> The instructions (pg. 48) say to set the RF GAIN control fully
>> clockwise, measure the voltage on pin 5 of U2 on the control board,
>> and adjust trimmer R1 for a reading of 3.80 volts.
>>
>> I did my voltage measurements with my own (cheap) DMM, not the
>> internal voltmeter.
>>
>> My concern is that, by adjusting R1, the highest I could get the
>> voltage to go was 3.59v, so for the moment, that's where it's set.
>>
>> I measured the voltage on the LM2930T-8, and it has 12.23V at the
>> input, but only 7.53V at the output. The 78M05 has 4.93V at its
>> output.
>>
>> When I rotate the AF GAIN control, I get a range of 4.68V (fully
>> counter-clockwise) to 3.59V (fully clockwise) on pin 5 of U2.
>>
>> My power supply is a small benchtop power supply; it's putting out
>> 12.4V, and reports the K2 is drawing about 100mA. When I measure the
>> input voltage across the K2 input jack, I get the same 12.4V.
>>
>> All of the previous checks were fine, and the following step, S-Meter
>> Alignment, seemed to work just fine.
>>
>> So, my question is, do I have a problem? Should I be concerned?
>>
>> Thanks,
>>
>> Sarah AF6FH
>
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>

Michael Baker-3

RE: AGC Threshold Ok! (was Re: K2: AGC Threshold Too Low?)

In reply to this post by Sarah K.

Hello Sarah,

Having spent 10 years or so in apartments trying to operate HF I can
recommend a couple of things to improve your evaluation of the K2.
GET THE ANTENNA OUTSIDE AND IF POSSIBE MAKE IT REASONATE. I had a
friend give me the remains of a couple of Hustler mobile antenna setups
including two masts and 2 40 and 2 20 meter resonators. I used a mount I got
at the time from a CB store to make a rotatable dipole and put it on a
camera tripod with duct tape.
Not pretty but it fit on the patio for the first test and made a
usable receive antenna.
Later I made an extension mast from the pole off a pool skimmer and
put it in a TV tripod and just stood it on my balcony lashed to the handrail
with bungee cords.
This put the antenna up and away from the building which was stucco
over wire and block. This type of construction acts like a faraday shield
and won't let you hear diddly.
I had to put it up and down each day I intended to use it so the
mgmnt wouldn't have a fit but it worked well enough to keep me from being
QRT.
Good luck with your K2 project. You have the greatest resource at
your fingertips with the company and this reflector so failure is unlikely.
I know we will hear you on the air at some point. ;>)

Michael Baker K7DD
[hidden email]

-----Original Message-----
From: [hidden email]
[mailto:[hidden email]] On Behalf Of Sarah K
Sent: Sunday, December 02, 2007 1:58 AM
To: [hidden email]
Subject: [Elecraft] AGC Threshold Ok! (was Re: K2: AGC Threshold Too Low?)

Hi All,

Good news... I got my K2's replacement voltage regulator (LM2930T-8)
from Elecraft on Friday. Today I took out the old one and put in the
new one... the output of the voltage regulator is now 8.04 volts,
which is a whole lot better than the 7.53 volts I had gotten before!
And after adjusting R1, the AGC threshold is reading 3.80, exactly
where it should be!

Elecraft also sent me a replacement R116 which was missing (I think!)
so I was able to finish building Part II and move on to the alignment
and test for Part II.

Someone on the list (NM5B) had recommend I pick up a few of the
Elecraft mini-modules, so I ordered the noise generator, the 50uV
signal generator, and the dummy load. I put those together today too,
with no issues, and used them to help work through the alignment and
test.

On the whole, I was quite happy with the results of the alignment and
test; all of the instructions were fairly straightforward, and, even
better, my K2 seemed to pass all of them perfectly! Yay!

And the noise generator works; I can hear the noise. The signal
generator works, too; when I tune around 7040 kHz, I can hear the 40m
50uV oscillator.

Now comes my strange and possibly embarrassing question...

Um... should I be able to receive anything yet? Keep in mind, this is
my first radio... well, second, if you count my Yaesu VX-7R... and I
don't entirely know what to expect.

I have what is probably a very bad antenna; it's just two pieces of
random wire I had laying around, soldered onto a BNC connector, and
draped around the room. The total length is probably 20-25 feet,
which I *know* isn't the right length for 40 meters... but it was the
longest wire I had laying around. When I hook it to the K2 via a 3ft
BNC patch cable, I definitely hear an increase in the noise level in
the headphones.

But I wasn't able to tune into anything that sounded like an actual
transmission. No voice, no CW. I tried switching between CW, LSB, and
USB. And I fiddled with the filter settings.

I did hear a couple different kinds of things:

I hear whistling noises that increase or decrease in pitch as I tune
around.

I hear "pops" that happen when I tune across some small range of
frequencies. These pops seem to be mostly repeatable, as if I'm
hitting something in the same spot in the band, but I was never able
to tune in to anything.

I do also hear several places where the noise is louder, and the S-
meter increases by a notch or two... and once or twice I heard
something that could possibly have been very, very garbled speech.
But I wasn't ever able to tune into those, either, and in fact it
could have been my imagination.

And, so far... that's about it.

Some other things that might be worth pointing out: I have a high-
voltage transmission line and a substation about a block away from
me... and my antenna is parallel to it. And I connected the VX-7R to
the same antenna and it gets similar kinds of noise, and no signals
on 40m either. Also, I'm on the 2nd floor of an apartment, and an
outside antenna isn't going to be feasible here. I didn't try
grounding the K2 to the electrical ground yet... I certainly can't
install my own ground rod, either! I was running the K2 from 12 volts
worth of D batteries, to minimize power supply noise. And I turned
off all the fluorescent lights, which dropped the noise considerably,
but didn't reveal anything underneath the noise.

So... does this sound appropriate given the current situation? Should
I be hearing more than this? Am I not understanding how the K2 works?
Am I missing something very basic about ham radio? Am I doing
something silly? :-)

Should I try a better/different antenna? I now have about 150ft of
12ga stranded wire that I can use for a second test antenna; if I
run it perpendicular to the high voltage line I think I can go 40ft
in a mostly straight line, and probably 50ft with one right-angle
bend in it. I can't get to 67ft without some major contortions; my
apartment just isn't that big! I have the internal antenna tuner for
my K2 but of course I haven't put it together yet!

Or could there be something wrong with my partly-assembled K2?

To date, I've heard almost nothing on *any* HF band... once or twice
I've been able to hear faint strains of music on the VX-7R, when
using the pre-programmed "Shortwave Broacast" built-in memory. And I
have another little transistor radio that has shortwave bands on
it... and I've never heard anything on that either. Could I somehow
be in a location where I can't receive much of anything? (I do hear
stuff on VHF bands with the VX-7R.)

Suggestions/recommendations welcome!

Thanks,

Sarah AF6FH

On Nov 23, 2007, at 12:53 PM, Sarah K. wrote: [quoted bit corrected
for typos!]

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Jerry Flanders

Re: AGC Threshold Ok! (was Re: K2: AGC Threshold Too Low?)

In reply to this post by Kurt Pawlikowski

FYI - 50 microvolts is the widely accepted "S9" signal level, not 20
over. I would guess the 1uV is around S1, but not sure about that
one. More info in the Elecraft manual on the XG1 or XG2.

Jerry W4UK

At 10:43 AM 12/2/2007, Kurt Pawlikowski wrote:
>Sarah,
>... I'm told that in a properly adjusted (and complete?) radio, a 1
>micro-volt signal should register about S-3 and 50 micro-volt should
>be something like 20 db over 9.

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