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K2 receiver sensitivity on 12 and 10 Meters

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Hans J Rasmusen OZ7BQ

K2 receiver sensitivity on 12 and 10 Meters

My K2 (ser 04069) appears to lack a bit of receiver sensitivity on 12 and 10 Meters. I can hear stations and the static noise when the antenna is connected, only weaker than on other bands.
I have full TX power output on both bands, so the filters appears to be tuned correctly.I only noticed the apparent lower sensitivity on 12 and 10 Meters after adding a KX3 to the station.My plan is to rig the K2 up as second receiver for split operation on a special RX antenna using the K2 Rcvr Antenna module.
If the apparent lower sensitivity on 12 and 10 Meters is normal, so be it. However, I wonder if any one has made the same observations and found a solution.

Thank you in advance.73 Hans Jørgen (Joe) OZ7BQ

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vk2rq

Re: K2 receiver sensitivity on 12 and 10 Meters

If you are hearing a reasonable increase in atmospheric static noise when connecting an antenna on 12/10m, then any further increase in sensitivity is wasted and not making efficient use of the receiver's available dynamic range.

73,
Matt VK2RQ

> On 6 Nov 2014, at 8:41 am, Hans J Rasmusen OZ7BQ <[hidden email]> wrote:
>
> My K2 (ser 04069) appears to lack a bit of receiver sensitivity on 12 and 10 Meters. I can hear stations and the static noise when the antenna is connected, only weaker than on other bands.
> I have full TX power output on both bands, so the filters appears to be tuned correctly.I only noticed the apparent lower sensitivity on 12 and 10 Meters after adding a KX3 to the station.My plan is to rig the K2 up as second receiver for split operation on a special RX antenna using the K2 Rcvr Antenna module.
> If the apparent lower sensitivity on 12 and 10 Meters is normal, so be it. However, I wonder if any one has made the same observations and found a solution.
>
> Thank you in advance.73 Hans Jørgen (Joe) OZ7BQ
>
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Don Wilhelm-4

Re: K2 receiver sensitivity on 12 and 10 Meters

In reply to this post by Hans J Rasmusen OZ7BQ

Hans,

I would suggest you try re-peaking the K2 bandpass filters using
Transmit. Set the power to 2 watts and adjust the 10 meter inductors
for maximum output (L12 and L13) using TUNE, then switch to 12 meters
and adjust C44 and C46 for maximum output. That should produce the best
setting for both transmit and receive.

If connecting the antenna when tuned to those bands results in an
increase in noise in the receiver, you have all the sensitivity you can
use. You should be using real signals (but weak ones) to compare
receiver sensitivity - if you are comparing on the basis of the
'loudness' of the noise heard, that can create a false impression. What
is important is the signal that stands above the atmospheric noise.

73,
Don W3FPR

On 11/5/2014 4:41 PM, Hans J Rasmusen OZ7BQ wrote:
> My K2 (ser 04069) appears to lack a bit of receiver sensitivity on 12 and 10 Meters. I can hear stations and the static noise when the antenna is connected, only weaker than on other bands.
> I have full TX power output on both bands, so the filters appears to be tuned correctly.I only noticed the apparent lower sensitivity on 12 and 10 Meters after adding a KX3 to the station.My plan is to rig the K2 up as second receiver for split operation on a special RX antenna using the K2 Rcvr Antenna module.
> If the apparent lower sensitivity on 12 and 10 Meters is normal, so be it. However, I wonder if any one has made the same observations and found a solution.
>
>

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Hans J Rasmusen OZ7BQ

Re: K2 receiver sensitivity on 12 and 10 Meters

Dear Don and Matt,Thank you for your comments. I know that being able to hear the antenna noise, should indicate that the sensitivity is OK.Measuring the noise level on the K2 speaker output indicate that the noise level incease 4 to 6 dB on 10 Meters, but barely on 12 M when the antenna is connected. The difference is just audible, and the general RX signal level is lower than on other bands.Peaking the filter does not improve the RX. TX produce full output on both bands.
73 OZ7BQ Hans Jørgen

Den 0:44 torsdag den 6. november 2014 skrev Don Wilhelm <[hidden email]>:

Hans,

I would suggest you try re-peaking the K2 bandpass filters using
Transmit. Set the power to 2 watts and adjust the 10 meter inductors
for maximum output (L12 and L13) using TUNE, then switch to 12 meters
and adjust C44 and C46 for maximum output. That should produce the best
setting for both transmit and receive.

If connecting the antenna when tuned to those bands results in an
increase in noise in the receiver, you have all the sensitivity you can
use. You should be using real signals (but weak ones) to compare
receiver sensitivity - if you are comparing on the basis of the
'loudness' of the noise heard, that can create a false impression. What
is important is the signal that stands above the atmospheric noise.

73,
Don W3FPR

On 11/5/2014 4:41 PM, Hans J Rasmusen OZ7BQ wrote:
> My K2 (ser 04069) appears to lack a bit of receiver sensitivity on 12 and 10 Meters. I can hear stations and the static noise when the antenna is connected, only weaker than on other bands.
> I have full TX power output on both bands, so the filters appears to be tuned correctly.I only noticed the apparent lower sensitivity on 12 and 10 Meters after adding a KX3 to the station.My plan is to rig the K2 up as second receiver for split operation on a special RX antenna using the K2 Rcvr Antenna module.
> If the apparent lower sensitivity on 12 and 10 Meters is normal, so be it. However, I wonder if any one has made the same observations and found a solution.
>
>

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vk2rq

Re: K2 receiver sensitivity on 12 and 10 Meters

Here are some other ideas:

I wonder if switching off the AGC makes much difference? If so, maybe it is kicking in too early, and you may need to look at setting the threshold (I think there are procedures in the K2 manual for this).

You said peaking the band pass filter didn't help much (I guess you did this in the right order, as described in the manual?) What about the IF filter L34 adjustment? That could affect overall gain. Although not really related to sensitivity, while you are running alignment procedures, may as well go the whole way and check the setup of the crystal filter with spectrogram.

It may be interesting to measure the sensitivity to see if there may be a problem. The following webpage may be a useful reference:
http://www.cliftonlaboratories.com/k2_rx_sensitivity.htm

When I built my K2, I used the measurement procedure in the XG3 signal generator manual to measure the sensitivity as a sanity check to see if I'd built it properly. The result came out somewhere in the ballpark of the figure published in Rob Sherwood's receiver performance list.
http://www.sherweng.com/table.html

There is an application note on the Elecraft website dealing with increasing the K2 sensitivity, although as the article mentions, there are trade offs:
http://www.elecraft.com/Apps/RX_Gain_application_note.htm

73,
Matt VK2RQ

> On 7 Nov 2014, at 12:27 am, Hans J Rasmusen OZ7BQ <[hidden email]> wrote:
>
> Dear Don and Matt,Thank you for your comments. I know that being able to hear the antenna noise, should indicate that the sensitivity is OK.Measuring the noise level on the K2 speaker output indicate that the noise level incease 4 to 6 dB on 10 Meters, but barely on 12 M when the antenna is connected. The difference is just audible, and the general RX signal level is lower than on other bands.Peaking the filter does not improve the RX. TX produce full output on both bands.
> 73 OZ7BQ Hans Jørgen
>
>
> Den 0:44 torsdag den 6. november 2014 skrev Don Wilhelm <[hidden email]>:
>
>
> Hans,
>
> I would suggest you try re-peaking the K2 bandpass filters using
> Transmit. Set the power to 2 watts and adjust the 10 meter inductors
> for maximum output (L12 and L13) using TUNE, then switch to 12 meters
> and adjust C44 and C46 for maximum output. That should produce the best
> setting for both transmit and receive.
>
> If connecting the antenna when tuned to those bands results in an
> increase in noise in the receiver, you have all the sensitivity you can
> use. You should be using real signals (but weak ones) to compare
> receiver sensitivity - if you are comparing on the basis of the
> 'loudness' of the noise heard, that can create a false impression. What
> is important is the signal that stands above the atmospheric noise.
>
> 73,
> Don W3FPR
>
>> On 11/5/2014 4:41 PM, Hans J Rasmusen OZ7BQ wrote:
>> My K2 (ser 04069) appears to lack a bit of receiver sensitivity on 12 and 10 Meters. I can hear stations and the static noise when the antenna is connected, only weaker than on other bands.
>> I have full TX power output on both bands, so the filters appears to be tuned correctly.I only noticed the apparent lower sensitivity on 12 and 10 Meters after adding a KX3 to the station.My plan is to rig the K2 up as second receiver for split operation on a special RX antenna using the K2 Rcvr Antenna module.
>> If the apparent lower sensitivity on 12 and 10 Meters is normal, so be it. However, I wonder if any one has made the same observations and found a solution.
>>
>>
>
>
>
>
> ______________________________________________________________
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>
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Don Wilhelm-4

Re: K2 receiver sensitivity on 12 and 10 Meters

Matt and all,

While that is good info, be aware that the referenced application note
which suggests reducing the value of Control Board R1 is applicable only
to K2s below SN 3000.
There is a pot at R1 for the AGC Threshold level on all K2s SN 3000 and
above.

You can adjust the AGC Threshold lower than the suggested 3.8 volts, but
as you lower it, the values for CAL S LO and CAL S HI become more and
more erratic. I suggest keeping the voltage at CB U2 pin 5 to 6.5 volts
or higher - a minimum of 2.7 volts is normally sufficient.

73,
Don W3FPR

On 11/6/2014 12:31 PM, Matt VK2RQ wrote:
>
> There is an application note on the Elecraft website dealing with increasing the K2 sensitivity, although as the article mentions, there are trade offs:
> http://www.elecraft.com/Apps/RX_Gain_application_note.htm
>
> 73,
> Matt VK2RQ
>

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