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K3 on-channel strong signal overload?

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orbarrett

K3 on-channel strong signal overload?

Hello all,

I just finished operating my K3 from my friend's driveway using a portable dipole on 60M, and wanted to inquire about some incoming signal overload that cropped up. I was joined while ragchewing with some friends on 5371.5 by two other friends locally, one operating HF mobile from the same driveway and another operating from a base rig in the shack (using a backyard dipole antenna). When either of these two friends transmitted on the same channel (at 100W), I observed severe signal breakup in the K3 receive audio.

To investigate further, I switched the portable antenna from the K3 to my friend's FT-817 on the same operating table, and no audio breakup was observed under the same conditions. Returning the antenna to the K3, I then got rid of most of the signal breakup by turning on the input attenuator and turning down the RF gain to near minimum.

Is it possible that the extremely strong on-channel signal in this case is exceeding the ability of the K3's hardware AGC to protect the A/D converter input? Thanks for any suggestions on this, including anything I may have overlooked. AGC was enabled and both the NB and NR were switched off.

I should mention that these conditions of operating portable (with several hams close-in on the same channel) are very demanding, but happen occasionally in certain situations such as for HF Pack operating.
I'm also using the rig in HF mobile service, and enjoy it very much.

I appreciate any help in advance,
Oliver Barrett KB6BA

Steve Ellington

Re: K3 on-channel strong signal overload?

Oliver
I guess Elecraft will have to answer this one. Let us know what they say.
Steve Ellington
[hidden email]
----- Original Message -----
From: "orbarrett" <[hidden email]>
To: <[hidden email]>
Sent: Monday, May 04, 2009 12:39 AM
Subject: [Elecraft] K3 on-channel strong signal overload?

>
> Hello all,
>
> I just finished operating my K3 from my friend's driveway using a portable
> dipole on 60M, and wanted to inquire about some incoming signal overload
> that cropped up. I was joined while ragchewing with some friends on
> 5371.5
> by two other friends locally, one operating HF mobile from the same
> driveway
> and another operating from a base rig in the shack (using a backyard
> dipole
> antenna). When either of these two friends transmitted on the same
> channel
> (at 100W), I observed severe signal breakup in the K3 receive audio.
>
> To investigate further, I switched the portable antenna from the K3 to my
> friend's FT-817 on the same operating table, and no audio breakup was
> observed under the same conditions. Returning the antenna to the K3, I
> then
> got rid of most of the signal breakup by turning on the input attenuator
> and
> turning down the RF gain to near minimum.
>
> Is it possible that the extremely strong on-channel signal in this case is
> exceeding the ability of the K3's hardware AGC to protect the A/D
> converter
> input? Thanks for any suggestions on this, including anything I may have
> overlooked. AGC was enabled and both the NB and NR were switched off.
>
> I should mention that these conditions of operating portable (with several
> hams close-in on the same channel) are very demanding, but happen
> occasionally in certain situations such as for HF Pack operating.
> I'm also using the rig in HF mobile service, and enjoy it very much.
>
> I appreciate any help in advance,
> Oliver Barrett KB6BA
> --
> View this message in context:
> http://n2.nabble.com/K3-on-channel-strong-signal-overload--tp2785612p2785612.html
> Sent from the Elecraft mailing list archive at Nabble.com.
>
> ______________________________________________________________
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WILLIS COOKE

Re: K3 on-channel strong signal overload?

In reply to this post by orbarrett

I have had some similar observations on ten meters. After reading your report I am inclined to agree with you. I have a station about 5 miles away who I contact on a regular basis on 10 meters, both SSB and CW. He is usually very distorted here and I have not been able to understand because others on the net do not seem to observe the distortion. I have also heard a few stations with strong skip that seem the same way. I have not tried a different antenna, but turning off the pre-amp helps some and engaging the attenuator helps even more.

It makes sense to me that the front end overload clipping is activating and distorting the signal. It may not be such a problem now that I think I understand what is going on.

Willis 'Cookie' Cooke
K5EWJ

--- On Sun, 5/3/09, orbarrett <[hidden email]> wrote:

> From: orbarrett <[hidden email]>
> Subject: [Elecraft] K3 on-channel strong signal overload?
> To: [hidden email]
> Date: Sunday, May 3, 2009, 9:39 PM
> Hello all,
>
> I just finished operating my K3 from my friend's
> driveway using a portable
> dipole on 60M, and wanted to inquire about some incoming
> signal overload
> that cropped up. I was joined while ragchewing with some
> friends on 5371.5

Steve Ellington

Re: K3 on-channel strong signal overload?

I wonder if this could be caused by the TR switching diodes?

Steve Ellington
[hidden email]
----- Original Message -----
From: "WILLIS COOKE" <[hidden email]>
To: "orbarrett" <[hidden email]>; "Elecraft Reflector"
<[hidden email]>
Sent: Monday, May 04, 2009 11:51 AM
Subject: Re: [Elecraft] K3 on-channel strong signal overload?

>
> I have had some similar observations on ten meters. After reading your
> report I am inclined to agree with you. I have a station about 5 miles
> away who I contact on a regular basis on 10 meters, both SSB and CW. He
> is usually very distorted here and I have not been able to understand
> because others on the net do not seem to observe the distortion. I have
> also heard a few stations with strong skip that seem the same way. I have
> not tried a different antenna, but turning off the pre-amp helps some and
> engaging the attenuator helps even more.
>
> It makes sense to me that the front end overload clipping is activating
> and distorting the signal. It may not be such a problem now that I think
> I understand what is going on.
>
> Willis 'Cookie' Cooke
> K5EWJ
>
>
> --- On Sun, 5/3/09, orbarrett <[hidden email]> wrote:
>
>> From: orbarrett <[hidden email]>
>> Subject: [Elecraft] K3 on-channel strong signal overload?
>> To: [hidden email]
>> Date: Sunday, May 3, 2009, 9:39 PM
>> Hello all,
>>
>> I just finished operating my K3 from my friend's
>> driveway using a portable
>> dipole on 60M, and wanted to inquire about some incoming
>> signal overload
>> that cropped up. I was joined while ragchewing with some
>> friends on 5371.5
>
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:[hidden email]
>
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David Gilbert

Re: K3 on-channel strong signal overload?

In reply to this post by WILLIS COOKE

I don't think front end overload is your problem. I've had S9 + 45db
signals sound perfectly fine on my K3 with no audio distortion and no
off-frequency artifacts at all. I use the least amount of AGC possible
... AGC THR = 008 and AGC SLP = 000. The only way I've ever experienced
audio distortion is when I turn the AGC off.

On the other hand, K6LL and others have pointed out that the AF limiter
in the K3 kicks in a bit early even if it is set to the maximum of 30.
It's a pretty abrupt limiting action that can cause audio distortion,
and if you have yours set lower than 30 you'd probably hear problems
with even weaker signals.

Also, are you using a speaker, either an external one or the one in the
K3? You could be getting mechanical resonances on strong signals if you
are.

73,
Dave AB7E

WILLIS COOKE wrote:

> I have had some similar observations on ten meters. After reading your report I am inclined to agree with you. I have a station about 5 miles away who I contact on a regular basis on 10 meters, both SSB and CW. He is usually very distorted here and I have not been able to understand because others on the net do not seem to observe the distortion. I have also heard a few stations with strong skip that seem the same way. I have not tried a different antenna, but turning off the pre-amp helps some and engaging the attenuator helps even more.
>
> It makes sense to me that the front end overload clipping is activating and distorting the signal. It may not be such a problem now that I think I understand what is going on.
>
> Willis 'Cookie' Cooke
> K5EWJ
>
>
> --- On Sun, 5/3/09, orbarrett <[hidden email]> wrote:
>
>
>> From: orbarrett <[hidden email]>
>> Subject: [Elecraft] K3 on-channel strong signal overload?
>> To: [hidden email]
>> Date: Sunday, May 3, 2009, 9:39 PM
>> Hello all,
>>
>> I just finished operating my K3 from my friend's
>> driveway using a portable
>> dipole on 60M, and wanted to inquire about some incoming
>> signal overload
>> that cropped up. I was joined while ragchewing with some
>> friends on 5371.5
>>
>
>

Jim Brown-10

Re: K3 on-channel strong signal overload?

In reply to this post by orbarrett

On Sun, 3 May 2009 21:39:55 -0700 (PDT), orbarrett wrote:

>I was joined while ragchewing with some friends on 5371.5
>by two other friends locally, one operating HF mobile from the same driveway
>and another operating from a base rig in the shack (using a backyard dipole
>antenna). When either of these two friends transmitted on the same channel
>(at 100W), I observed severe signal breakup in the K3 receive audio.
Why are you surprised by this? This is entirely normal

>To investigate further, I switched the portable antenna from the K3 to my
>friend's FT-817 on the same operating table, and no audio breakup was
>observed under the same conditions. Returning the antenna to the K3, I then
>got rid of most of the signal breakup by turning on the input attenuator and
>turning down the RF gain to near minimum.

DUH! Why are you surprised by this? You had the K3 set for maximum
sensitivity and then hit it with a 100 watt transmitter. OF COURSE it's going
to overload! You probably had the preamp on too, which is entirely un-
necessary on 60M. The 817 is probably a much less sensitive radio, and may
have a more brute force AGC. The K3 will outperform it by 40-50 dB in
rejecting signals outside its passband.

The K3 is doing exactly what you SET its controls to do -- pull very weak
signals out of the mud. NO radio has infinite dynamic range. If you set it to
perform well on weak signals (preamp on, attenuator off, RF gain all the way
up), it's going to be badly overloaded by 100 watts ON FREQUENCY from an
antenna 30 feet away.

These are fundamental concepts of radio. It's too bad that they are seldom
taught today. Most of us old farts learned them as Novices when we put our
first rigs on the air. In those days, there were no transceivers. You had a
transmitter and you had a receiver, and when you transmitted your receiver
overloaded.

73,

Jim Brown K9YC

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Mike Harris-9

Re: K3 on-channel strong signal overload?

In reply to this post by David Gilbert

G'day,

I have a neighbour, VP8LP only 300 metres away. If I drop onto his
frequency when he transmits the S-meter doesn't have enough digits to
display. Only when my beam is pointing at him do I notice anything
untoward on the audio. This goes away as soon as I switch on the
attenuator or rotate the beam. We can usually work the same band, me on
CW, Bob on SSB, both QRO.

I'm inclined to go with K9YC.

Regards,

Mike VP8NO
(old fart)

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Steve Ellington

Re: K3 on-channel strong signal overload?

In reply to this post by Jim Brown-10

This "Duhing" is entirely unfair. Didn't you read what he said? The author
stated that he had the pre-amp off, RF gain at minimum, NB off, NR off and
ATTN turned on. What more could he do to eliminate the overload? Without
looking, I believe the MDS of the K3 and the FT-817 are probably similar on
60 meters. I believe he did everything possible with his settings. I still
believe the problem could be the switching diodes producing IMD from that
super strong signal and there may not be an easy cure.
Steve Ellington
[hidden email]
----- Original Message -----
From: "Jim Brown" <[hidden email]>
To: <[hidden email]>
Sent: Monday, May 04, 2009 1:01 PM
Subject: Re: [Elecraft] K3 on-channel strong signal overload?

> On Sun, 3 May 2009 21:39:55 -0700 (PDT), orbarrett wrote:
>
>>I was joined while ragchewing with some friends on 5371.5
>>by two other friends locally, one operating HF mobile from the same
>>driveway
>>and another operating from a base rig in the shack (using a backyard
>>dipole
>>antenna). When either of these two friends transmitted on the same
>>channel
>>(at 100W), I observed severe signal breakup in the K3 receive audio.
> Why are you surprised by this? This is entirely normal
>
>>To investigate further, I switched the portable antenna from the K3 to my
>>friend's FT-817 on the same operating table, and no audio breakup was
>>observed under the same conditions. Returning the antenna to the K3, I
>>then
>>got rid of most of the signal breakup by turning on the input attenuator
>>and
>>turning down the RF gain to near minimum.
>
> DUH! Why are you surprised by this? You had the K3 set for maximum
> sensitivity and then hit it with a 100 watt transmitter. OF COURSE it's
> going
> to overload! You probably had the preamp on too, which is entirely un-
> necessary on 60M. The 817 is probably a much less sensitive radio, and
> may
> have a more brute force AGC. The K3 will outperform it by 40-50 dB in
> rejecting signals outside its passband.
>
> The K3 is doing exactly what you SET its controls to do -- pull very weak
> signals out of the mud. NO radio has infinite dynamic range. If you set it
> to
> perform well on weak signals (preamp on, attenuator off, RF gain all the
> way
> up), it's going to be badly overloaded by 100 watts ON FREQUENCY from an
> antenna 30 feet away.
>
> These are fundamental concepts of radio. It's too bad that they are seldom
> taught today. Most of us old farts learned them as Novices when we put our
> first rigs on the air. In those days, there were no transceivers. You had
> a
> transmitter and you had a receiver, and when you transmitted your receiver
> overloaded.
>
> 73,
>
> Jim Brown K9YC
>
>
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
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Jim Brown-10

Re: K3 on-channel strong signal overload?

In reply to this post by orbarrett

On Mon, 4 May 2009 13:36:18 -0400, Randy Downs wrote:

>I see distortion with a 40 over signal. 35 to 40 over seems to be when
>I see it. Preamp on.

So turn the preamp off! Preamps are for weak signals on the higher HF
bands. Preamps should NEVER be used below 20 meters, and rarely on 20M.

Steve said:

>This "Duhing" is entirely unfair. Didn't you read what he said?

Yes, and he said he got rid of most of the overload by minimizing the
gain of the K3. The receiver in the K3 is a thoroughbred, "souped up" to
copy weak signals with other strong signals AROUND them. It uses a lot of
IF selectivity to do that. 100W ON FREQUENCY in the same driveway is an
extreme case -- the IF filtering can't do anything at all. I suggest that
you compute the voltage at the antenna terminals of the radio for the
scenario described in the post. It is unreasonable to expect a souped up
and well protected receiver to be completely free of overload under this
condition.

Have you ever worked a ham through a VHF repeater when you're less than a
city block apart? It is VERY common for the other ham's transmitter to
desense your receiver so that you can't hear the repeater! What's
happening is that the other guy's transmitter is biasing your front end
into cutoff (even with 600 kHz spacing on VHF, 5 MHz spacing on UHF).

The K3 doesn't do that -- it keeps on working. But there is protection
circuitry in the front end that prevents a big signal from frying
something. Remember -- the K3 is not ONLY a QRP rig. Many hams use K3s in
big contesting stations with legal limit amplifiers and SO2R -- that is,
listening on one frequency while transmitting on another with a second
radio. Those field strengths can fry the front end of a receiver that
isn't well protected. The K3 IS protected. The small distortion he's
hearing is part of the cost of that protection.

73,

Jim Brown K9YC

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Mike Harris-9

Re: K3 on-channel strong signal overload?

In reply to this post by Steve Ellington

Hi,

Just been looking through my archives. I remembered that there was a
simple mod to the K2 to overcome audio distortion in an extreme overload
environment, I installed it on my K2 and it was totally immune to
co-channel audio distortion when my very near neighbour VP8LP transmitted:

"K2 - Improved Handling of Extremely strong (and nearby) Signals".

Maybe the K3 architecture offers similar opportunities.

Regards,

Mike VP8NO

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Jim Brown-10

Re: K3 on-channel strong signal overload?

In reply to this post by orbarrett

On Mon, 4 May 2009 14:12:09 -0400, Randy Downs wrote:

>It's on 10 meters. Should I not run 10 meters?

Of course not. Just don't be surprised when several volts of on-
frequency RF causes overload.

73,

Jim K9YC

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Don Wilhelm-4

Re: K3 on-channel strong signal overload?

In reply to this post by Mike Harris-9

Mike,

That mod to the K2 (which has been incorporated into the new K2s) is
simply a limiter.
If the signal level at the input to the IF amplifier ever increases to
the point where the diodes clip the signal, then distortion will occur.
The clippping distortion may not be noticed on CW, but it certainly will
distort SSB and data signals.

There is a mod for the K3 to change to a larger choke in the AF
amplifier. If that change is not installed, distortion can occur in the
AF amp itself.

But all in all, Jim Brown is correct - a large signal like what was
reported is certain to cause activation of the COR at the K3 input
(input protection) and distortion is to be expected in situations like
that. It is also likely that the K3 Hardware AGC is maxed out and can
lower the gain no more with the resulting of overload of the ADC.
Without making measurements, it is difficult to say just where the
overload point(s) might have been, but it is clear that a 100 watt
signal ON FREQUENCY with antennas close to each other is certain to
create overload and the distortion is a natural 'happening' under such
overload conditions -- in other words, the K3 dynamic range (as good as
it is) was exceeded - everything has its limits.

73,
Don W3FPR

Mike Harris wrote:

> Hi,
>
> Just been looking through my archives. I remembered that there was a
> simple mod to the K2 to overcome audio distortion in an extreme overload
> environment, I installed it on my K2 and it was totally immune to
> co-channel audio distortion when my very near neighbour VP8LP transmitted:
>
> "K2 - Improved Handling of Extremely strong (and nearby) Signals".
>
> Maybe the K3 architecture offers similar opportunities.
>
> Regards,
>
> Mike VP8NO
>
>

WILLIS COOKE

Re: K3 on-channel strong signal overload?

In reply to this post by Jim Brown-10

Why are we throwing stones? The K-3 is different than other transceivers that we have used. In the heat of a contest or chasing DX one does not always immediately make sense of what is happening. Sharing some observations about characteristics of Elecraft products along with ways of dealing with a peculiarity is one of the great benefits of this forum. It took several episodes and a post from a fellow K-3 owner for the light to dawn on me. I never saw this problem with my BC-455, my S-53, my Hammarlund Super-Pro. Turning off the preamp and kicking on the attenuator work very well, but one has to think about it. Now that we have thoroughly discussed the subject we will probably all remember to do it. Unfortunately many of us will be reluctant to admit to having confusion and offer our experience and solution for fear of someone calling us stupid. I will not have that problem because I really don't care if someone calls me stupid.

Willis 'Cookie' Cooke
K5EWJ

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wayne burdick

Re: K3 on-channel strong signal overload?

Administrator

In reply to this post by Jim Brown-10

I haven't ever experienced a problem with strong on-channel overload
with the K3. But it's possible that you're hitting it with so much
power that you're putting one or more RX stages into saturation,
possibly including the I.F. amp. (In an extreme case, you could even be
exceeding the useful range of the TR switch PIN diodes. The FT817, if
I'm not mistaken, uses a TR relay.)

While it's perfectly reasonable to expect the operator to turn on the
attenuator in such a situation, there may be a way to modify the K3 to
handle these signals, depending on where the saturation is occurring.
As an experiment, I would try adding back-to-back silicon diodes
(1N4148 or 1N914) at the output of the crystal filter and/or at the
output of the IF amp. The question is where to add them. One
possibility is across the primary of T5 in the IF amp, which would
drastically limit the max p-p voltage obtainable from this stage.
Another, less-invasive possibility would be across L39. At any normal
signal level the diodes would be essentially out of the circuit. On
large signals, they'd clamp the voltage at this point to about 1.4 Vpp.

73,
Wayne
N6KR

---

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P.B. Christensen

Re: K3 on-channel strong signal overload?

> (In an extreme case, you could even be
> exceeding the useful range of the TR switch PIN diodes. The FT817, if
> I'm not mistaken, uses a TR relay.)

Some "scratch-paper" calculations in a 50-ohm system:

Assuming it really is the T/R PIN diodes, they would conduct at just under
one volt. In a 50-ohm system (and highly dependent on the PIN
configuration), that's roughly a 10 dBm signal -- or stated another way, 10
mW of power dissipated at the Rx front end.

It would be an interesting exercise to momentarily bypass the T/R PIN diodes
and re-test with the same driveway setup. So, even if this really is the
cause, it would probably be a safe assumption that the K3 will still handle
strong signals far better than most other receivers -- until an outrageously
high value begins conducting PIN diodes. That solution might call for
replacement of the solid-state T/R with a relay.

Thanks, but "no thanks."

Paul, W9AC

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Mike Harris-9

Re: K3 on-channel strong signal overload?

In reply to this post by Don Wilhelm-4

Hi Don,

Quote
The two diodes limit the signal to 1.4 V peak-to-peak. Even when the
diodes are conducting, i.e. when the signal

is so strong that it looks like a square wave at pin 4, there is no
audible signal distortion. This is because the

MC1350 is followed by a second crystal filter which removes any harmonic
distortion products (i.e. multiples of

4.915 MHz). The diodes appear to have no other side-effects.

Unquote.

Indeed, no distortion noted CW or SSB.

Regards,

Mike VP8NO

----- Original Message -----
From: "Don Wilhelm" <[hidden email]>
To: "Mike Harris" <[hidden email]>
Cc: "Reflector Elecraft" <[hidden email]>
Sent: Monday, May 04, 2009 2:47 PM
Subject: Re: [Elecraft] K3 on-channel strong signal overload?

| Mike,
|
| That mod to the K2 (which has been incorporated into the new K2s) is
| simply a limiter.
| If the signal level at the input to the IF amplifier ever increases to
| the point where the diodes clip the signal, then distortion will occur.
| The clippping distortion may not be noticed on CW, but it certainly will
| distort SSB and data signals.

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K8RDD

Re: K3 on-channel strong signal overload?

In reply to this post by Jim Brown-10

40 over is several volts? I thought it was around 5 mili volts. That's what
I am talking about. I've seen this distortion in signals since several fw
revisions ago. If I get time tonight I'll reload some earlier rev's.
Randy
K8RDD
----- Original Message -----
From: "Jim Brown" <[hidden email]>
To: "Elecraft List" <[hidden email]>
Sent: Monday, May 04, 2009 2:34 PM
Subject: Re: [Elecraft] K3 on-channel strong signal overload?

> On Mon, 4 May 2009 14:12:09 -0400, Randy Downs wrote:
>
>>It's on 10 meters. Should I not run 10 meters?
>
> Of course not. Just don't be surprised when several volts of on-
> frequency RF causes overload.
>
> 73,
>
> Jim K9YC
>
>
> ______________________________________________________________
> Elecraft mailing list
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kd4d

Re: K3 on-channel strong signal overload?

In reply to this post by orbarrett

Good day:

I can't help myself. :-)

The "usual" definition of an S9 signal is 50 uVolts, or -73 dBm (assuming a
50 Ohm load).

The "S-Meter" unit is a 6 dB change in VOLTAGE, not power. To get one VOLT,
we need 2000 times 50 uVolts, or S9 + about 86dB (86 dB over S9).

40 over is about 5 mVolts...

The formula for the dB difference for two voltages, assuming you want a power
and have the same load, is

20 * log (V2/V1). If you want dB's "over" S9, let V1 be 50 uV, (50E-6 Volts).

Now, let's hope I managed to get this right. :-)

73,

Mark

----- Original Message -----
From: "Randy Downs" <[hidden email]>
To: [hidden email], "Jim Brown" <[hidden email]>
Sent: Monday, May 4, 2009 4:37:01 PM GMT -05:00 US/Canada Eastern
Subject: Re: [Elecraft] K3 on-channel strong signal overload?

40 over is several volts? I thought it was around 5 mili volts. That's what
I am talking about. I've seen this distortion in signals since several fw
revisions ago. If I get time tonight I'll reload some earlier rev's.
Randy
K8RDD
----- Original Message -----
From: "Jim Brown" <[hidden email]>
To: "Elecraft List" <[hidden email]>
Sent: Monday, May 04, 2009 2:34 PM
Subject: Re: [Elecraft] K3 on-channel strong signal overload?

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Jim Brown-10

Re: K3 on-channel strong signal overload?

On Mon, 4 May 2009 21:10:46 +0000 (UTC), [hidden email] wrote:

>Now, let's hope I managed to get this right. :-)

Nothing wrong with your math. The likely error is in assuming that
ANY S-meter is accurate at the extremes of its range. All the S-
meters I've seen compress both at the top and bottom of their range.
As others have noted, the protection diodes will conduct to limit
the input that the receiver sees to about a volt, even though those
diodes may be seeing more. When those diodes conduct they will
produce some distortion. That's the nature of diodes.

Note also that the circuits driving the S-meter in the K3 can be set
to correct for the gain added by the preamp and subtracted by the
attenuator, or not. And, of course, you've got to calibrate the S-
meter with a voltage source of known accuracy.

73,

Jim K9YC

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n7ws

Re: K3 on-channel strong signal overload?

In reply to this post by kd4d

--- On Mon, 5/4/09, [hidden email] <[hidden email]> wrote:

> From: [hidden email] <[hidden email]>
> Subject: Re: [Elecraft] K3 on-channel strong signal overload?
> To: [hidden email]
> Date: Monday, May 4, 2009, 3:10 PM
> Good day:
>
> I can't help myself. :-)
>
> The "usual" definition of an S9 signal is 50
> uVolts, or -73 dBm (assuming a
> 50 Ohm load).
>
> The "S-Meter" unit is a 6 dB change in VOLTAGE,
> not power. To get one VOLT,
> we need 2000 times 50 uVolts, or S9 + about 86dB (86 dB
> over S9).
>
> 40 over is about 5 mVolts...
>
> The formula for the dB difference for two voltages,
> assuming you want a power
> and have the same load, is
>
> 20 * log (V2/V1). If you want dB's "over"
> S9, let V1 be 50 uV, (50E-6 Volts).
>
> Now, let's hope I managed to get this right. :-)

You got the right answer (86 dB) but when using your slide rule you didn't keep track of the decimal point. One volt is 20,000 * 50 uV.

Wes Stewart, N7WS

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123