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A question about low sensitivity

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Joseph Reed-2

A question about low sensitivity

Hi guys,

Been a while since I last kept up with the list. You were a great source of help back when I built K2 #1133. Now I have #5226 and have completed the second section of construction. The receiver works, I can hear stations on 40. Yesterday I listed to Mid-Cars, Southcars, and Eastcars. But they were only moderatly loud and I had AF gain full out. On the IC-756 Pro they were booming.

On the radio I thought the AGC voltage might have been too high. 3.80 volts on the nose. T-34 tunes very well, as do L-1 and L-2. Every other test and alignment to this point was well within specs. Any ideas as to why it is not hearing well? Or should I not be concerned at this stage of construction and press on to stage 3.

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Don Wilhelm-3

RE: A question about low sensitivity

It is difficult to suggest just where the problem may be. It could simply
be a matter of filter alignment, or it could be something not right in the
receiver path.
Since the receive path is now complete (although the front end is now built
only for 40 meters). so you can either debug it now or later. If you choose
to do it later, you could encounter some difficulty discerning the proper
adjustment of the bandpass filters for the initial receive alignment.

I would suggest that you follow the steps in the receiver signal tracing
section (Troubleshooting appendix in the manual). If you do not have a
signal source of sufficient amplitude, you can build the oscillator shown in
the manual, or you might want to first try Tom Hammond's 'Quick and Dirty
Signal Tracing' techniques that you can obtain from the Elecraft website.

Proceed in an orderly manner to determine the failing stage or section first
and then you can quickly home in on the actual component that is giving you
trouble.

Of course, the most likely failure is a faulty soldering connection or a
misplaced component, so your first step should be the check soldering, then
re-check the soldering, and after you have done that - check the soldering.

73,
Don W3FPR

> -----Original Message-----
>
> Been a while since I last kept up with the list. You were a
> great source of help back when I built K2 #1133. Now I have
> #5226 and have completed the second section of construction. The
> receiver works, I can hear stations on 40. Yesterday I listed to
> Mid-Cars, Southcars, and Eastcars. But they were only moderatly
> loud and I had AF gain full out. On the IC-756 Pro they were booming.
>
> On the radio I thought the AGC voltage might have been too
> high. 3.80 volts on the nose. T-34 tunes very well, as do L-1
> and L-2. Every other test and alignment to this point was well
> within specs. Any ideas as to why it is not hearing well? Or
> should I not be concerned at this stage of construction and press
> on to stage 3.
>
>

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Jim Younce

Re: A question about low sensitivity

In reply to this post by Joseph Reed-2

Joe:

I suggest that you check the installation of C6 the 4.7 pf disc located on
the very back of the board between L1 and L2. This capacitor shouold be
installed so that there is an empty hole between the two leads. You
actually install it in a spot for a jack that is installed if you install
the 60Meter Module. Many guys install this capacitor on the two holes
closest to the left edge of the board and when you do there is no coupling
capacitor connected between L1 and L2. This might not be your problem but
it is sure worth a quick look see.

73
Jim K4ZM

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Don Brown-4

Re: A question about low sensitivity

In reply to this post by Joseph Reed-2

Hi

Double check T7. Make sure the green winding is in 1 and 2 and the red
winding is in 3 and 4 closest to the IC U12. If it is backwards the
sensitivity will be low, the audio will be low and the AGC will not work
properly although everything else will appear OK.

Don Brown

KD5NDB

----- Original Message -----
From: "Joseph Reed" <[hidden email]>
To: <[hidden email]>
Sent: Wednesday, December 28, 2005 8:35 AM
Subject: [Elecraft] A question about low sensitivity

> Hi guys,
>
> Been a while since I last kept up with the list. You were a great
> source of help back when I built K2 #1133. Now I have #5226 and have
> completed the second section of construction. The receiver works, I can
> hear stations on 40. Yesterday I listed to Mid-Cars, Southcars, and
> Eastcars. But they were only moderatly loud and I had AF gain full out.
> On the IC-756 Pro they were booming.
>
> On the radio I thought the AGC voltage might have been too high. 3.80
> volts on the nose. T-34 tunes very well, as do L-1 and L-2. Every other
> test and alignment to this point was well within specs. Any ideas as to
> why it is not hearing well? Or should I not be concerned at this stage of
> construction and press on to stage 3.
>
>
> _______________________________________________
> 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
>

Robert McGwier

Re: A question about low sensitivity

Been there, done that. After you swap it (should you find it is
backwards), protect your ears by turning down the audio first. ;-).

HNY to all!
Bob
N4HY

Don Brown wrote:

>Hi
>
>Double check T7. Make sure the green winding is in 1 and 2 and the red
>winding is in 3 and 4 closest to the IC U12. If it is backwards the
>sensitivity will be low, the audio will be low and the AGC will not work
>properly although everything else will appear OK.
>
>Don Brown
>
>KD5NDB
>
>
>----- Original Message -----
>From: "Joseph Reed" <[hidden email]>
>To: <[hidden email]>
>Sent: Wednesday, December 28, 2005 8:35 AM
>Subject: [Elecraft] A question about low sensitivity
>
>
>
>
>>Hi guys,
>>
>> Been a while since I last kept up with the list. You were a great
>>source of help back when I built K2 #1133. Now I have #5226 and have
>>completed the second section of construction. The receiver works, I can
>>hear stations on 40. Yesterday I listed to Mid-Cars, Southcars, and
>>Eastcars. But they were only moderatly loud and I had AF gain full out.
>>On the IC-756 Pro they were booming.
>>
>> On the radio I thought the AGC voltage might have been too high. 3.80
>>volts on the nose. T-34 tunes very well, as do L-1 and L-2. Every other
>>test and alignment to this point was well within specs. Any ideas as to
>>why it is not hearing well? Or should I not be concerned at this stage of
>>construction and press on to stage 3.
>>
>>
>>_______________________________________________
>>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
>>
>>
>>
>_______________________________________________
>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
>
>
>
>

--
AMSAT VP Engineering. Member: ARRL, AMSAT-DL, TAPR, Packrats,
NJQRP/AMQRP, QRP ARCI, QCWA, FRC. ARRL SDR Wrk Grp Chairman
Laziness is the number one inspiration for ingenuity. Guilty as charged!

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Joseph Reed-2

Re: A question about low sensitivity

In reply to this post by Don Brown-4

Hi Don,

You nailed it I put T-7 in backwards. <Duh!>. As soon as I put it in correctly, well it sounds like a K-2 ought to.

The K-2 was a Christmas gift from my XYL and I am enjoying the build. With this problem solved Phase II of construction is complete. I must call the House of Elecraft for more options so I can continue the experience.

73,
Joe N9JR

Don Brown <[hidden email]> wrote:
Hi

Double check T7. Make sure the green winding is in 1 and 2 and the red
winding is in 3 and 4 closest to the IC U12. If it is backwards the
sensitivity will be low, the audio will be low and the AGC will not work
properly although everything else will appear OK.

Don Brown

KD5NDB

----- Original Message -----
From: "Joseph Reed"
To:
Sent: Wednesday, December 28, 2005 8:35 AM
Subject: [Elecraft] A question about low sensitivity

VR2BrettGraham

Re: A question about low sensitivity

In reply to this post by Joseph Reed-2

Compared against other rigs here, my K2 (24xx) seems deaf & more
so on some bands.

Much less so now after aligning the BPFs with spec-an & tracking
gen - but still noticeable.

This was before narrowing BPFs so as to avoid AGC responding to
out-of-band energy & may still be due in part to AGC even after
trying LA3ZA mod (a noticeable improvement, but seems to need
_much_ more help than that, at least in this part of R3 with decent
antennas).

It became very obvious tuning across the band after adding LA3ZA
mod that sensitivity varies depending on energy level at the AGC
image frequency.

But this apparently is not an issue in either R1 or R2.

73 & HNY/HLNY, VR2BrettGraham

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Don Wilhelm-3

RE: A question about low sensitivity

Brett,

Since you suspect that the receiver is being de-sensed by the AGC, try
turning the AGC off and controlling the level with the RF Gain. If things
seem more 'normal' that way, I suggest you try adding a filter to the AGC
IF - see LA3ZA's mod page for 2 examples of how to do that.

73,
Don W3FPR

> -----Original Message-----
> From: [hidden email]
> [mailto:[hidden email]]On Behalf Of VR2BrettGraham
> Sent: Thursday, December 29, 2005 7:39 AM
> To: [hidden email]
> Subject: Re: [Elecraft] A question about low sensitivity
>
>
> Compared against other rigs here, my K2 (24xx) seems deaf & more
> so on some bands.
>
> Much less so now after aligning the BPFs with spec-an & tracking
> gen - but still noticeable.
>
> This was before narrowing BPFs so as to avoid AGC responding to
> out-of-band energy & may still be due in part to AGC even after
> trying LA3ZA mod (a noticeable improvement, but seems to need
> _much_ more help than that, at least in this part of R3 with decent
> antennas).
>
> It became very obvious tuning across the band after adding LA3ZA
> mod that sensitivity varies depending on energy level at the AGC
> image frequency.
>
> But this apparently is not an issue in either R1 or R2.
>
> 73 & HNY/HLNY, VR2BrettGraham
>

VR2BrettGraham

RE: A question about low sensitivity

W3FPR suggested:

>Since you suspect that the receiver is being de-sensed by the AGC, try
>turning the AGC off and controlling the level with the RF Gain. If things
>seem more 'normal' that way, I suggest you try adding a filter to the AGC
>IF - see LA3ZA's mod page for 2 examples of how to do that.

As I mentioned below, both BPFs have been tightened up (DL7ARJ?)
& selectivity in AGC chain (LA3ZA) have been implemented.

Where the AGC does not seem to be choking my K2, all I need is
switch to another rig in order to copy the desired signal. When the
AGC dominates, obviously things get better on another rig.

Disabling the AGC on the K2 - where I know the AGC is not
responding to an image - results in only the slightest change,
so presumably it's close to where it needs to be.

On the bench, MDS is somewhere below lowest output level of
my sig gen (Marconi 2017... -131 dBm) & although it's just an
indication, once set there's quite a variation in what it takes to
achieve the same S-meter reading on different bands.

Nothing untoward seen when sweeping/peaking the BPFs, yet
the rig seems somewhat deaf without the AGC image response
rearing its ugly head & that deafness varies between bands -
almost like there's some sort of suck-out downstream of the
BPFs or other difference in response that is not necessarily
proportional to frequency.

Not sure what's wrong with my K2 - perhaps this is actually
normal behavior & my expectations of its performance are
unrealistic - but one thing I can say is that I wish I had peaked
the BPFs with spec-an/tracking-gen earlier as doing so has
made a big difference over what can be achieved otherwise &
this may also be something others may want to keep in mind
(most bands picked up about a dB & more importantly, response
across some bands flattened by 3-5 dB).

But my K2 still is inferior to a TS-950S with its horrific audio
IMD & spurs across the output that is as good as torture to
listen to - those really weak long path signals at bottom of
cycle simply are below what this K2 can hear.

73 & HNY/HLNY, VR2BrettGraham

> > -----Original Message-----
> > From: [hidden email]
> > [mailto:[hidden email]]On Behalf Of VR2BrettGraham
> > Sent: Thursday, December 29, 2005 7:39 AM
> > To: [hidden email]
> > Subject: Re: [Elecraft] A question about low sensitivity
> >
> >
> > Compared against other rigs here, my K2 (24xx) seems deaf & more
> > so on some bands.
> >
> > Much less so now after aligning the BPFs with spec-an & tracking
> > gen - but still noticeable.
> >
> > This was before narrowing BPFs so as to avoid AGC responding to
> > out-of-band energy & may still be due in part to AGC even after
> > trying LA3ZA mod (a noticeable improvement, but seems to need
> > _much_ more help than that, at least in this part of R3 with decent
> > antennas).
> >
> > It became very obvious tuning across the band after adding LA3ZA
> > mod that sensitivity varies depending on energy level at the AGC
> > image frequency.
> >
> > But this apparently is not an issue in either R1 or R2.
> >
> > 73 & HNY/HLNY, VR2BrettGraham