K3 Digital Mode Settings

[David Herring-2]

Aloha from Hawaii!

As this is my first post to this reflector, I suppose I should introduce myself...I'm Dave, K6DCH.  QTH Kauai, Hawaii, and I am the satisfied owner/operator of K3 Serial # 3019.  :-)

I've been reading the various posts recently about how to set up for digital modes using the Data mode on the K3.  I have also been reading the other posts about how to set the ACG, the RF gain, etc.  A question comes to mind about this:

Does the advice on dialing back the RF gain, as tendered on this reflector, apply to when one is running digital?  For example, I've recently started playing with Olivia since it is noted for weak signal robustness.  Would I run the rig with the RF gain wide open, or would I still dial it back to the point where the S meter just stops flickering?  My first instinct is to run with the RF gain more open than that since Olivia communications succeed at signal levels below the noise floor, but I wanted to do something of a sanity check amongst other K3 users to see if I'm thinking about this right or not.

I have benefited greatly by reading this reflector and appreciate everyone's contributions.

All the best,

Dave, K6DCH
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[Don Wilhelm-4]

Dave,

It all depends.  The recommendations for adjusting the RF Gain control
to "just barely hear band noise" is aimed at those who are listening to
the K3 audio with headphones (or a speaker).  Since signals that are
below the band noise level cannot usually be copied, there is no sense
in listening to the band noise, so backing off the RF gain is a prudent
thing to do given these assumptions.  That applies to signals that are
normally heard with the ear/brain combination.

Digital modes can sometimes decode signals that are below the band noise
level (and there is no need to listen to the trash on the band with
one's ears).  If one is receiving a digital signal that has this
capability, one would want to set the RF Gain control to a point where
some band noise is evident - how much you might ask, and the answer is -
how many dB below the ambient noise will result in good copy of the
digital signal?.  That answer will vary from digital mode to digital mode.

73,
Don W3FPR

David Herring wrote:

> Aloha from Hawaii!
>
> As this is my first post to this reflector, I suppose I should introduce myself...I'm Dave, K6DCH.  QTH Kauai, Hawaii, and I am the satisfied owner/operator of K3 Serial # 3019.  :-)
>
> I've been reading the various posts recently about how to set up for digital modes using the Data mode on the K3.  I have also been reading the other posts about how to set the ACG, the RF gain, etc.  A question comes to mind about this:
>
> Does the advice on dialing back the RF gain, as tendered on this reflector, apply to when one is running digital?  For example, I've recently started playing with Olivia since it is noted for weak signal robustness.  Would I run the rig with the RF gain wide open, or would I still dial it back to the point where the S meter just stops flickering?  My first instinct is to run with the RF gain more open than that since Olivia communications succeed at signal levels below the noise floor, but I wanted to do something of a sanity check amongst other K3 users to see if I'm thinking about this right or not.
>
> I have benefited greatly by reading this reflector and appreciate everyone's contributions.
>  
>

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[Julian, G4ILO]

I agree with Don. It all depends. And the advice you read related to modes like CW and SSB that are received by listening to them.

The thing with digital modes is that, unlike other modes, it is quite common to receive using a bandwidth that lets many signals through simultaneously. The decoding software doesn't care, since it is using a brick wall DSP filter centered on the signal you are decoding.

The problem is AGC. If a strong signal appears in the passband then it will cause the gain to be depressed and that could adversely affect the S/N ratio of the signal you are trying to receive.

There are two ways round that. One is to turn AGC off, and regulate the gain using the RF Gain control. This will prevent the signal level varying as signals come and go within the passband. The other is to use narrow filtering to exclude all but the wanted signal. That is the way to extract the best possible copy from a weak signal, but it's more work and not necessary for the majority of contacts.

[David Herring-2]

Joe, Don, Julian,

Thanks for the responses.  You've got me thinking along the right track now.

73 and Aloha,

Dave, K6DCH

On Dec 26, 2009, at 5:28 PM, David Herring wrote:

> Aloha from Hawaii!
>
> As this is my first post to this reflector, I suppose I should introduce myself...I'm Dave, K6DCH.  QTH Kauai, Hawaii, and I am the satisfied owner/operator of K3 Serial # 3019.  :-)
>
> I've been reading the various posts recently about how to set up for digital modes using the Data mode on the K3.  I have also been reading the other posts about how to set the ACG, the RF gain, etc.  A question comes to mind about this:
>
> Does the advice on dialing back the RF gain, as tendered on this reflector, apply to when one is running digital?  For example, I've recently started playing with Olivia since it is noted for weak signal robustness.  Would I run the rig with the RF gain wide open, or would I still dial it back to the point where the S meter just stops flickering?  My first instinct is to run with the RF gain more open than that since Olivia communications succeed at signal levels below the noise floor, but I wanted to do something of a sanity check amongst other K3 users to see if I'm thinking about this right or not.
>
> I have benefited greatly by reading this reflector and appreciate everyone's contributions.
>
> All the best,
>
> Dave, K6DCH
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:[hidden email]
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html

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