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K3: RF Gain, Squelch

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Phil Hystad

K3: RF Gain, Squelch

I have never really understood the connection between RF gain and squelch controls. I first saw this when I got my first modern rig, the Icom 756 Pro III. And, I see this kind of combo with the K3 too. I never had experience with this back in my early ham operator days (~1960s).

So, can someone explain the behavior. Let's assume that I have squelch operative for FM only.

On CW or SSB I see that RF gain maximized is the control knob turned all the way clockwise. But, as I back off the RF gain (counterclockwise) there comes a point where the S-meter starts to increase even though there is no apparent signal. Turning the RF gain fully counter clockwise pins the S-meter.

So, what is going on here. What is this connection between turning "down" RF gain and the S-meter increasing. Now, I have the same behavior (roughly) on my Icom Pro III and I never understood that either.

Thanks for any explanation you can contribute.

73, phil, K7PEH
K3 owner for one full week now.
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Alan Bloom

Re: K3: RF Gain, Squelch

On most radios, the term "RF Gain" is actually a misnomer. The control
should really be called "IF Gain".

The way most HF receivers work is that turning down the "RF Gain"
control simply applies a DC voltage to the receiver's AGC circuitry.
For example, if an S9 signal causes the AGC voltage to rise to 1.23
volts, then when you set the RF Gain control to place 1.23V on the AGC
line, the S meter will read S9 even when no signal is present. In that
case, signals below S9 do not change the gain or S meter reading.
Signals above S9 cause the AGC/S meter to rise as before.

Turning down the RF gain control causes the receiver to sound less noisy
because the IF gain is limited to some maximum value. If you set it
right you can still hear the weak signals (taking advantage of the human
ear's dynamic range) but you don't have to put up with so much noise.

On the noisy low bands I generally set the RF Gain control so that the S
meter reads nearly constant when no signals are present, bouncing up
slightly only on the biggest noise peaks.

Al N1AL

On Mon, 2010-01-11 at 20:11 -0800, Phil Hystad wrote:

> I have never really understood the connection between RF gain and squelch controls. I first saw this when I got my first modern rig, the Icom 756 Pro III. And, I see this kind of combo with the K3 too. I never had experience with this back in my early ham operator days (~1960s).
>
> So, can someone explain the behavior. Let's assume that I have squelch operative for FM only.
>
> On CW or SSB I see that RF gain maximized is the control knob turned all the way clockwise. But, as I back off the RF gain (counterclockwise) there comes a point where the S-meter starts to increase even though there is no apparent signal. Turning the RF gain fully counter clockwise pins the S-meter.
>
> So, what is going on here. What is this connection between turning "down" RF gain and the S-meter increasing. Now, I have the same behavior (roughly) on my Icom Pro III and I never understood that either.
>
> Thanks for any explanation you can contribute.
>
> 73, phil, K7PEH
> K3 owner for one full week now.
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
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>
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> Please help support this email list: http://www.qsl.net/donate.html

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Don Wilhelm-4

Re: K3: RF Gain, Squelch

In reply to this post by Phil Hystad

Phil,

It is quite normal for the S-meter reading to increase when the RF gain
is reduced. The AGC voltage (which drives the S-meter) is increased to
reduce the gain of the receiver when the RF Gain is reduced - so the
S-meter indication goes up.

The way I tend to think of it is - there is already an S-3 level of
atmospheric (and locally generated) noise on a particular band, so I
reduce the RF Gain until the S-meter reads S-3 and the band noise does
not bother me. Signals stronger than the band noise will still make the
S-meter increase, so I can still see a relative signal strength reading
between stations.

If you want to reduce the signal level into the K3 without changing the
S-meter, set the menu to S-MTR ABS (S-meter absolute) and turn off the
preamp and possibly turn on the Attenuator. In ABS mode, the S-meter
will not change with preamp or attenuator on/off, but it will still rise
with reduction of the RF Gain. For maximum performance on any
particular band, if you can hear the band noise (with no signal
present), turn the preamp off (it is not needed and is detrimental to
the receiver dynamic range) - if the band noise is still present, turn
on the attenuator. If you can still hear the band noise, reduce the RF
gain to the point where the band noise is just barely audible - that is
the maximum sensitivity setting that can be used for that band. Note
than this optimum setting will change from time to time, and from band
to band. The K3 has more than ample gain so it can hear very weak
signals - if the band noise is high, you are unlikely to hear signals
below that band noise level, so it is wise to reduce the receiver gain
to keep the receiver from sounding "noisy".

This is different than squelch. Squelch totally silences (mutes) the
receiver until a signal greater than the level set by the squelch
control is exceeded.

Does that help?

73,
Don W3FPR

Phil Hystad wrote:

Don Wilhelm-4

Re: K3: RF Gain, Squelch

In reply to this post by Alan Bloom

Al,

To look at it another way - look at the S-meter to observe the band
noise level, and then back off the RF gain until the S-meter is steady
at that same S-meter reading. Of course, this should be done at a spot
in the band where no signals are present.

That is a quick way to determine the optimum setting for the RF Gain
consistent with the greatest receiver dynamic range and one does not
have to listen to the constant band noise clutter.

The other option is to just run with "all knobs full right" and put up
with listening to the band noise when there are gaps in the signal level.

Be aware that the AGC Threshold will also have a great effect on the
amount of band noise heard in the audio. If the Threshold is set too
low, the receiver will go into AGC action on only the band noise. I use
an AGC Threshold setting of 008 just for that reason (I know the default
is 005, but I think that is too low).

73,
Don W3FPR

Alan Bloom wrote:

> On most radios, the term "RF Gain" is actually a misnomer. The control
> should really be called "IF Gain".
>
> The way most HF receivers work is that turning down the "RF Gain"
> control simply applies a DC voltage to the receiver's AGC circuitry.
> For example, if an S9 signal causes the AGC voltage to rise to 1.23
> volts, then when you set the RF Gain control to place 1.23V on the AGC
> line, the S meter will read S9 even when no signal is present. In that
> case, signals below S9 do not change the gain or S meter reading.
> Signals above S9 cause the AGC/S meter to rise as before.
>
> Turning down the RF gain control causes the receiver to sound less noisy
> because the IF gain is limited to some maximum value. If you set it
> right you can still hear the weak signals (taking advantage of the human
> ear's dynamic range) but you don't have to put up with so much noise.
>
> On the noisy low bands I generally set the RF Gain control so that the S
> meter reads nearly constant when no signals are present, bouncing up
> slightly only on the biggest noise peaks.
>
> Al N1AL
>
>
>

Phil Hystad

Re: K3: RF Gain, Squelch

Don and Al...

Thanks for the explanations. Yes, this does indeed make sense. Finally that mystery is behind me.

phil

On Jan 11, 2010, at 9:10 PM, Don Wilhelm wrote:

> Al,
>
> To look at it another way - look at the S-meter to observe the band noise level, and then back off the RF gain until the S-meter is steady at that same S-meter reading. Of course, this should be done at a spot in the band where no signals are present.
>
> That is a quick way to determine the optimum setting for the RF Gain consistent with the greatest receiver dynamic range and one does not have to listen to the constant band noise clutter.
>
> The other option is to just run with "all knobs full right" and put up with listening to the band noise when there are gaps in the signal level.
>
> Be aware that the AGC Threshold will also have a great effect on the amount of band noise heard in the audio. If the Threshold is set too low, the receiver will go into AGC action on only the band noise. I use an AGC Threshold setting of 008 just for that reason (I know the default is 005, but I think that is too low).
>
> 73,
> Don W3FPR
>
> Alan Bloom wrote:
>> On most radios, the term "RF Gain" is actually a misnomer. The control
>> should really be called "IF Gain".
>>
>> The way most HF receivers work is that turning down the "RF Gain"
>> control simply applies a DC voltage to the receiver's AGC circuitry.
>> For example, if an S9 signal causes the AGC voltage to rise to 1.23
>> volts, then when you set the RF Gain control to place 1.23V on the AGC
>> line, the S meter will read S9 even when no signal is present. In that
>> case, signals below S9 do not change the gain or S meter reading.
>> Signals above S9 cause the AGC/S meter to rise as before.
>>
>> Turning down the RF gain control causes the receiver to sound less noisy
>> because the IF gain is limited to some maximum value. If you set it
>> right you can still hear the weak signals (taking advantage of the human
>> ear's dynamic range) but you don't have to put up with so much noise.
>>
>> On the noisy low bands I generally set the RF Gain control so that the S
>> meter reads nearly constant when no signals are present, bouncing up
>> slightly only on the biggest noise peaks.
>>
>> Al N1AL
>>
>>

gm3sek

Re: K3: RF Gain, Squelch

In reply to this post by Alan Bloom

Alan Bloom wrote:
>On most radios, the term "RF Gain" is actually a misnomer. The control
>should really be called "IF Gain".
>

This includes the K3; manual RF gain control or AGC are not applied to
any stage ahead of the first mixer.

The "RF Gain" control operates on only one stage, the 8.215MHz IF
amplifier, which is also controlled by the hardware AGC.

The only controls in the K3 that affect signal levels *ahead* of the
first mixer are the PREamp and ATTenuator buttons - just two steps of
about 10dB each.

--

73 from Ian GM3SEK
http://www.ifwtech.co.uk/g3sek
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w7aqk

Re: K3: RF Gain, Squelch

In reply to this post by Don Wilhelm-4

Don and All,

Your last post raises a question in my mind--it probably has been discussed
before, and if so, I missed it. I must admit that the number of posts on
this reflector is often overwhelming, and I'm sure I get too quick with the
delete key.

Here's the question--I bought the 6 khz filter, but not the 13 khz filter.
I don't do AM, and probably won't do much, if any FM, but I suppose the
possibility is there for a very small amount of FM on 10 meters perhaps.
Anyway, I bought the 6 khz filter, primarily to accomodate any SW listening
I might do. So, would I have been better off to buy the 13 khz filter
instead of the 6 khz filter? That sounds like what you did. I assume I
could just use the 13 khz filter for AM listening, and use the DSP to narrow
things appropriately. I wouldn't have a 6 khz roofing filter, but would I
really be at much of a disadvantage for the type of use I describe above?
For some reason, I thought the 6 khz filter was mandatory for AM, but maybe
I misread that (or misinterpreted what I think I read!).

By the way, your discussion of how to set the RF gain makes a great deal of
sense to me. It is, in fact, what I have been doing intuitively. My RF
gain is almost always set at something like 12 o'clock or so--maybe a tad
bit higher. My "excursion range" with the RF gain rarely goes beyond the 2
o'clock position, even on very weak signals. Beyond that all I seem to be
doing is increasing the noise level with little or no improvement in the
desired signal. I rarely use the preamp, and find that it more often than
not degrades what I am trying to hear.

Dave W7AQK

----- Original Message -----
From: "Don Wilhelm" <[hidden email]>
To: <[hidden email]>
Cc: "Elecraft Discussion List" <[hidden email]>
Sent: Monday, January 11, 2010 10:10 PM
Subject: Re: [Elecraft] K3: RF Gain, Squelch

> Al,
>
> To look at it another way - look at the S-meter to observe the band
> noise level, and then back off the RF gain until the S-meter is steady
> at that same S-meter reading. Of course, this should be done at a spot
> in the band where no signals are present.
>
> That is a quick way to determine the optimum setting for the RF Gain
> consistent with the greatest receiver dynamic range and one does not
> have to listen to the constant band noise clutter.
>
> The other option is to just run with "all knobs full right" and put up
> with listening to the band noise when there are gaps in the signal level.
>
> Be aware that the AGC Threshold will also have a great effect on the
> amount of band noise heard in the audio. If the Threshold is set too
> low, the receiver will go into AGC action on only the band noise. I use
> an AGC Threshold setting of 008 just for that reason (I know the default
> is 005, but I think that is too low).
>
> 73,
> Don W3FPR
>

Don Wilhelm-4

Re: K3: RF Gain, Squelch

Dave,

The 6 kHz filter is mandatory for AM and/or ESSB *transmit*.
For AM receive only, the 6 kHz IF bandpass reduces to a maximum AF
frequency of 3 kHz after de-modulation of both sidebands.
The 13 kHz "FM" filter can certainly be used for AM receive, and the K3
audio response can go as high as 4 kHz (that is the limit set in the
DSP). If you encounter AM stations that are strong and are on adjacent
frequencies, then the 13 kHz filter may be too wide.

So how to obtain a full audio bandwidth with AM and the 6 kHz filter? -
that has now been answered with the inclusion of Sync AM reception -
that only uses one of the sidebands, the SHIFT knob changes from USB to
LSB, so one can enjoy the full audio bandwidth that the K3 offers using
that mode. Your 6 kHz filter is NOT a 'waste' after all.

73,
Don W3FPR

David Y. wrote:

> Don and All,
>
> Your last post raises a question in my mind--it probably has been
> discussed before, and if so, I missed it. I must admit that the
> number of posts on this reflector is often overwhelming, and I'm sure
> I get too quick with the delete key.
>
> Here's the question--I bought the 6 khz filter, but not the 13 khz
> filter. I don't do AM, and probably won't do much, if any FM, but I
> suppose the possibility is there for a very small amount of FM on 10
> meters perhaps. Anyway, I bought the 6 khz filter, primarily to
> accomodate any SW listening I might do. So, would I have been better
> off to buy the 13 khz filter instead of the 6 khz filter? That sounds
> like what you did. I assume I could just use the 13 khz filter for AM
> listening, and use the DSP to narrow things appropriately. I wouldn't
> have a 6 khz roofing filter, but would I really be at much of a
> disadvantage for the type of use I describe above? For some reason, I
> thought the 6 khz filter was mandatory for AM, but maybe I misread
> that (or misinterpreted what I think I read!).
>
> By the way, your discussion of how to set the RF gain makes a great
> deal of sense to me. It is, in fact, what I have been doing
> intuitively. My RF gain is almost always set at something like 12
> o'clock or so--maybe a tad bit higher. My "excursion range" with the
> RF gain rarely goes beyond the 2 o'clock position, even on very weak
> signals. Beyond that all I seem to be doing is increasing the noise
> level with little or no improvement in the desired signal. I rarely
> use the preamp, and find that it more often than not degrades what I
> am trying to hear.
>
> Dave W7AQK
>
>
> ----- Original Message ----- From: "Don Wilhelm" <[hidden email]>
> To: <[hidden email]>
> Cc: "Elecraft Discussion List" <[hidden email]>
> Sent: Monday, January 11, 2010 10:10 PM
> Subject: Re: [Elecraft] K3: RF Gain, Squelch
>
>
>> Al,
>>
>> To look at it another way - look at the S-meter to observe the band
>> noise level, and then back off the RF gain until the S-meter is steady
>> at that same S-meter reading. Of course, this should be done at a spot
>> in the band where no signals are present.
>>
>> That is a quick way to determine the optimum setting for the RF Gain
>> consistent with the greatest receiver dynamic range and one does not
>> have to listen to the constant band noise clutter.
>>
>> The other option is to just run with "all knobs full right" and put up
>> with listening to the band noise when there are gaps in the signal
>> level.
>>
>> Be aware that the AGC Threshold will also have a great effect on the
>> amount of band noise heard in the audio. If the Threshold is set too
>> low, the receiver will go into AGC action on only the band noise. I use
>> an AGC Threshold setting of 008 just for that reason (I know the default
>> is 005, but I think that is too low).
>>
>> 73,
>> Don W3FPR
>>
>