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K2 and NaP3 IF offset values

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K8AC

K2 and NaP3 IF offset values

I've been using my K2 with LP-Pan and NaP3 for a few months on the lower bands and just recently got on 20 and 15 meter CW with it. I found that the offsets you specify in NaP3 were considerably different on 15, 12 and 10 meters while that for 20M was just a bit off from the lower bands. 17M offset was the same as the lower bands. For example, the global offset required on 80, 40 and 30M is 1170 in my case. For 20M, it's 1200. For 15M it's (-285) and (-330) for 10M.

When I say the "offset required", that means the value I need to specify in order for the NaP3 center frequency indicator line to be exactly in the middle of a received CW signal.

Not quite sure why the offset difference - obviously the IF signal is not exactly the same for all bands, but why not?

Don Wilhelm-4

Re: K2 and NaP3 IF offset values

Floyd,

Rather than centering the signal on a CW signal, center it on the
carrier of an AM signal. A CW signal should display offset from the
center by the amount of your sidetone pitch.

The K2 uses high side VFO injection for bands below 15 meters. For 15
meters and above, it uses low side VFO injection. That is the reason
you are seeing the change on 15 meters and above.

73,
Don W3FPR

On 11/14/2015 11:15 AM, K8AC wrote:

> I've been using my K2 with LP-Pan and NaP3 for a few months on the lower
> bands and just recently got on 20 and 15 meter CW with it. I found that the
> offsets you specify in NaP3 were considerably different on 15, 12 and 10
> meters while that for 20M was just a bit off from the lower bands. 17M
> offset was the same as the lower bands. For example, the global offset
> required on 80, 40 and 30M is 1170 in my case. For 20M, it's 1200. For 15M
> it's (-285) and (-330) for 10M.
>
> When I say the "offset required", that means the value I need to specify in
> order for the NaP3 center frequency indicator line to be exactly in the
> middle of a received CW signal.
>
> Not quite sure why the offset difference - obviously the IF signal is not
> exactly the same for all bands, but why not?
>
>

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vk2rq

Re: K2 and NaP3 IF offset values

In reply to this post by K8AC

For bands below 15m, the K2 sets the VCO so that the LSB image from the first mixer falls within the crystal filter, however for 15m and 10m it uses the USB image (since VCO only goes up to 24MHz or so). When you are in CW mode, you want the baseband to be LSB. This means for 80m-17m, you need to put the BFO below the filter passband, since the output of the 1st mixer is already LSB, but for 15m and 10m the output of the 1st mixer was USB, so you need to flip it by placing the BFO above the filter passband. This is why the perceived offset on NaP3 goes negative for the upper bands. Maybe you remember when you did the CAL FIL procedure, one of the parameters you had to set was in fact the BFO frequency.

Why is there a difference between 20m and 80m-30m? I’m guessing maybe you are using a different filter on 20m, which has a slightly different BFO offset. For 15m and 10m, if you use a different filter, the change in BFO offset will be even more significant, since when you set the width of the filter, it mainly affects the upper edge of the passband, and so the BFO offset must be adjusted to compensate (remembering that for 15m and 10m the BFO is set above the passband rather than below).

--
73 de Matt VK2RQ

On 15 novembre 2015 at 3:16:21 AM, K8AC ([hidden email]) wrote:

I've been using my K2 with LP-Pan and NaP3 for a few months on the lower
bands and just recently got on 20 and 15 meter CW with it. I found that the
offsets you specify in NaP3 were considerably different on 15, 12 and 10
meters while that for 20M was just a bit off from the lower bands. 17M
offset was the same as the lower bands. For example, the global offset
required on 80, 40 and 30M is 1170 in my case. For 20M, it's 1200. For 15M
it's (-285) and (-330) for 10M.

When I say the "offset required", that means the value I need to specify in
order for the NaP3 center frequency indicator line to be exactly in the
middle of a received CW signal.

Not quite sure why the offset difference - obviously the IF signal is not
exactly the same for all bands, but why not?

--
View this message in context: http://elecraft.365791.n2.nabble.com/K2-and-NaP3-IF-offset-values-tp7610348.html
Sent from the Elecraft mailing list archive at Nabble.com.
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K8AC

Re: K2 and NaP3 IF offset values

I suspect that the difference I saw in the offset for 20M was indeed due to a different filter selection. If I center the signal on the NaP3 indicator using my most-often-used 400 Hz filter, advancing through subsequent narrower filters I see just a bit of movement of the signal relative to the pointer. But, with the two wider filter positions, the movement is substantial and would require a much larger or smaller offset in NaP3 to get the signal aligned with the pointer.

With a bit of work, I can probably get the signal and pointer pretty much aligned by tweaking the BFO settings for the wider filters. I'll watch the shape and position with Spectrogram while doing that.

By the way, this isn't just an academic exercise. When I'm operating split and chasing DX, I often need to be able to position the transmit VFO pointer on a signal and have the K2 exactly on that frequency and not a couple hundred Hz away.

vk2rq

Re: K2 and NaP3 IF offset values

Understood. If you use CW-R on 15m & 10m, then that will help you match up the BFO frequency on those bands, as again the BFO will be placed on the low side of the crystal filter pass band, although the pitch you hear as you tune up the band will go high to low instead of low to high. To really fix this this up properly though would require some enhancements to NaP3. Not sure if the author ever released the source code though.
73, Matt VK2RQ

On Sat, Nov 14, 2015 at 12:29 PM -0800, "K8AC" <[hidden email]> wrote:

I suspect that the difference I saw in the offset for 20M was indeed due to a
different filter selection. If I center the signal on the NaP3 indicator
using my most-often-used 400 Hz filter, advancing through subsequent
narrower filters I see just a bit of movement of the signal relative to the
pointer. But, with the two wider filter positions, the movement is
substantial and would require a much larger or smaller offset in NaP3 to get
the signal aligned with the pointer.

With a bit of work, I can probably get the signal and pointer pretty much
aligned by tweaking the BFO settings for the wider filters. I'll watch the
shape and position with Spectrogram while doing that.

By the way, this isn't just an academic exercise. When I'm operating split
and chasing DX, I often need to be able to position the transmit VFO pointer
on a signal and have the K2 exactly on that frequency and not a couple
hundred Hz away.

--
View this message in context: http://elecraft.365791.n2.nabble.com/K2-and-NaP3-IF-offset-values-tp7610348p7610356.html
Sent from the Elecraft mailing list archive at Nabble.com.
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K8AC

Re: K2 and NaP3 IF offset values

NaP3 already includes the ability to set different offsets for CW and CW-R and those offsets are used in conjunction with the global offset which applies to all modes. To make it work for the upper bands, you'd need to be able to specify a separate global offset value based on the band you're on. I'm afraid there isn't much interest in making things work right for the K2 at this point. I see that NaP3 has the ability to poll the rig for the IF frequency and filter shift and that appears to be for the K3. I don't believe the K2 has the ability to respond to those commands.

N8LP

Re: K2 and NaP3 IF offset values

In reply to this post by K8AC

The K2 changes the LO injection from high side to low side above 17m.
Early versions of NaP3 and PowerSDR/IF had an option box that allowed
the user to enter a frequency for K2 (and for K3) which reverses the
sidebands at a specified frequency, but later versions should do this
automatically at the correct frequency. I'm not sure which version
you're using, and I haven't used my K2 with LP-PAN since I got a K3, so
maybe there's a bug in some of the newer versions.

Larry N8LP

On 11/14/2015 11:31 PM, [hidden email] wrote:

> Date: Sat, 14 Nov 2015 09:15:43 -0700 (MST)
> From: K8AC<[hidden email]>
> To:[hidden email]
> Subject: [Elecraft] K2 and NaP3 IF offset values
> Message-ID:<[hidden email]>
> Content-Type: text/plain; charset=us-ascii
>
> I've been using my K2 with LP-Pan and NaP3 for a few months on the lower
> bands and just recently got on 20 and 15 meter CW with it. I found that the
> offsets you specify in NaP3 were considerably different on 15, 12 and 10
> meters while that for 20M was just a bit off from the lower bands. 17M
> offset was the same as the lower bands. For example, the global offset
> required on 80, 40 and 30M is 1170 in my case. For 20M, it's 1200. For 15M
> it's (-285) and (-330) for 10M.
>
> When I say the "offset required", that means the value I need to specify in
> order for the NaP3 center frequency indicator line to be exactly in the
> middle of a received CW signal.
>
> Not quite sure why the offset difference - obviously the IF signal is not
> exactly the same for all bands, but why not?

N8LP

Re: K2 and NaP3 IF offset values

> On 11/14/2015 11:31 PM, [hidden email] wrote:
>> Date: Sat, 14 Nov 2015 09:15:43 -0700 (MST)
>> From: K8AC<[hidden email]>
>> To:[hidden email]
>> Subject: [Elecraft] K2 and NaP3 IF offset values
>> Message-ID:<[hidden email]>
>> Content-Type: text/plain; charset=us-ascii
>>
>> I've been using my K2 with LP-Pan and NaP3 for a few months on the lower
>> bands and just recently got on 20 and 15 meter CW with it. I found
>> that the
>> offsets you specify in NaP3 were considerably different on 15, 12 and 10
>> meters while that for 20M was just a bit off from the lower bands. 17M
>> offset was the same as the lower bands. For example, the global offset
>> required on 80, 40 and 30M is 1170 in my case. For 20M, it's 1200.
>> For 15M
>> it's (-285) and (-330) for 10M.
>>
>> When I say the "offset required", that means the value I need to
>> specify in
>> order for the NaP3 center frequency indicator line to be exactly in the
>> middle of a received CW signal.
>>
>> Not quite sure why the offset difference - obviously the IF signal is
>> not
>> exactly the same for all bands, but why not?
>

K8AC

Re: K2 and NaP3 IF offset values

Yep - I'm aware of the K2 difference on the higher bands. I'm running V4 RC3, and it definitely does not correct the change on the higher bands. I've not tried the earlier V4 version or any V3 version with the K2, so can't shed any light on when things might have gone bad. I'm also using LPB-2 and that seems to work flawlessly with the K2.

73, Floyd - K8AC