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SSB Power

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Matt Osborn

SSB Power

I'm a little confused about measured transmitted power when in SSB vs
CW.

As an example, I have an XV50 Transverter that is adjusted to produce
20 watts RF out when using the K2 'tune' control. This output is
adjusted by reading 20 watts on an external power meter. The power
indicator LEDs are then adjusted to read 20 watts as well.

When using SSB, however, the RF out is much, much lower, maxing out at
7-8 watts PEP on the external power meter. The indicator LEDs,
however, indicate 10 - 20 watts of power.

I'm not certain I know how to understand what it is I'm measuring. In
my mind, I think much the 20 watts RF out of a CW signal is actually
carrier and of not much use. When in SSB, I want to think that I can
still put out the 20 watts, only now all concentrated in one sideband.

Why does the power meter fail to show the 20 watts?
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Ron D'Eau Claire-2

RE: SSB Power

-----Original Message-----
Matt wrote:

I'm a little confused about measured transmitted power when in SSB vs CW.

As an example, I have an XV50 Transverter that is adjusted to produce 20
watts RF out when using the K2 'tune' control. This output is adjusted by
reading 20 watts on an external power meter. The power indicator LEDs are
then adjusted to read 20 watts as well.

When using SSB, however, the RF out is much, much lower, maxing out at 7-8
watts PEP on the external power meter. The indicator LEDs, however,
indicate 10 - 20 watts of power.

I'm not certain I know how to understand what it is I'm measuring. In my
mind, I think much the 20 watts RF out of a CW signal is actually carrier
and of not much use. When in SSB, I want to think that I can still put out
the 20 watts, only now all concentrated in one sideband.

Why does the power meter fail to show the 20 watts?

_______________________________________________

Of course CW is ONLY carrier, on and off, so the information is in the
keying. But when the key is down, you are putting out full power.

Your transverter should be configured to put 20 watts out when driven at
either 5 watts or 1 mW, key down in CW mode, depending upon whether you have
the K60XV interface installed in your K2 and are using the RF output at the
antenna connector or the K60XV connection.

When your K2 is in TUNE, the power is reduced and no longer controlled by
the K2's automatic power controlling system. That's so you can tune up with
an ATU and the K2 won't go nuts trying to adjust its power output as the SWR
changes. If you set up your transverter for 20 watts output with the K2 in
TUNE, you may overdrive it in normal operation.

SSB has a very low duty cycle. That is, the average power output is far, far
below the peaks. You can raise the average power a bit using the K2's speech
compression, but its average is still well below the peak CW level. The very
brief transient peaks in your voice will hit full 20 watts out and unless
your Power meter is designed to register peak RF and not average RF (like
most meters) it'll show a much, much lower RF AVERAGE output even though
your voice peaks are hitting 20 watts. The LED display on the transverter
(and K2's RF bargraph) show the actual output, so you'll see them both
flicker on voice peaks.

Ron AC7AC

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N8LP

Re: SSB Power

It depends on the wattmeter. If the wattmeter had a PEP or peak-hold
mode, it would show the actual peak power. Many simple meters are
affected by the duty cycle of the signal, especially analog ones where
ballistics come into play.

There are a number of meters on the market that show peak power. One you
can build is my LP-100 project which is featured on the cover of the
latest QEX. You can read more about it and the simpler LP-300 kit on my
website... link below. They are both digital with peak-hold, but also
have very fast pseudo-analog bargraph displays that track voice peaks.

Larry N8LP
www.telepostinc.com

Ron D'Eau Claire wrote:

>-----Original Message-----
>Matt wrote:
>
>I'm a little confused about measured transmitted power when in SSB vs CW.
>
>As an example, I have an XV50 Transverter that is adjusted to produce 20
>watts RF out when using the K2 'tune' control. This output is adjusted by
>reading 20 watts on an external power meter. The power indicator LEDs are
>then adjusted to read 20 watts as well.
>
>When using SSB, however, the RF out is much, much lower, maxing out at 7-8
>watts PEP on the external power meter. The indicator LEDs, however,
>indicate 10 - 20 watts of power.
>
>I'm not certain I know how to understand what it is I'm measuring. In my
>mind, I think much the 20 watts RF out of a CW signal is actually carrier
>and of not much use. When in SSB, I want to think that I can still put out
>the 20 watts, only now all concentrated in one sideband.
>
>Why does the power meter fail to show the 20 watts?
>
> _______________________________________________
>
>Of course CW is ONLY carrier, on and off, so the information is in the
>keying. But when the key is down, you are putting out full power.
>
>Your transverter should be configured to put 20 watts out when driven at
>either 5 watts or 1 mW, key down in CW mode, depending upon whether you have
>the K60XV interface installed in your K2 and are using the RF output at the
>antenna connector or the K60XV connection.
>
>When your K2 is in TUNE, the power is reduced and no longer controlled by
>the K2's automatic power controlling system. That's so you can tune up with
>an ATU and the K2 won't go nuts trying to adjust its power output as the SWR
>changes. If you set up your transverter for 20 watts output with the K2 in
>TUNE, you may overdrive it in normal operation.
>
>SSB has a very low duty cycle. That is, the average power output is far, far
>below the peaks. You can raise the average power a bit using the K2's speech
>compression, but its average is still well below the peak CW level. The very
>brief transient peaks in your voice will hit full 20 watts out and unless
>your Power meter is designed to register peak RF and not average RF (like
>most meters) it'll show a much, much lower RF AVERAGE output even though
>your voice peaks are hitting 20 watts. The LED display on the transverter
>(and K2's RF bargraph) show the actual output, so you'll see them both
>flicker on voice peaks.
>
>Ron AC7AC
>
>_______________________________________________
>Elecraft mailing list
>Post to: [hidden email]
>You must be a subscriber to post to the list.
>Subscriber Info (Addr. Change, sub, unsub etc.):
> http://mailman.qth.net/mailman/listinfo/elecraft
>
>Help: http://mailman.qth.net/subscribers.htm
>Elecraft web page: http://www.elecraft.com
>
>
>
>
>

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Don Wilhelm-3

RE: SSB Power

In reply to this post by Matt Osborn

Matt,

I would surmise that you are being confused by your external wattmeter. The
XV50 LEDs will flash on voice peaks, but if your wattmeter is showing you
average power, its indication will be much less than the peak power.

This 'confusion' leads many folks to overdrive their equipment on SSB. The
K2 has a good indicator in the ALC LED display. If you see the ALC
indicator lighted at all, you are driving to the proper peak power. This
can be observed easily on an oscilloscope - first observe the amplitude of
your power setting in CW, and then switch to SSB. If the voice peaks come
up to the same amplitude as you observed for the CW signal, you are
achieving that same level of PEP (peak envelope power). The average power
will be considerably less than the PEP power for SSB.

73,
Don W3FPR

> -----Original Message-----
>
> I'm a little confused about measured transmitted power when in SSB vs
> CW.
>
> As an example, I have an XV50 Transverter that is adjusted to produce
> 20 watts RF out when using the K2 'tune' control. This output is
> adjusted by reading 20 watts on an external power meter. The power
> indicator LEDs are then adjusted to read 20 watts as well.
>
> When using SSB, however, the RF out is much, much lower, maxing out at
> 7-8 watts PEP on the external power meter. The indicator LEDs,
> however, indicate 10 - 20 watts of power.
>
> I'm not certain I know how to understand what it is I'm measuring. In
> my mind, I think much the 20 watts RF out of a CW signal is actually
> carrier and of not much use. When in SSB, I want to think that I can
> still put out the 20 watts, only now all concentrated in one sideband.
>
> Why does the power meter fail to show the 20 watts?
> _______________________________________________
> Elecraft mailing list
> Post to: [hidden email]
> You must be a subscriber to post to the list.
> Subscriber Info (Addr. Change, sub, unsub etc.):
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> Help: http://mailman.qth.net/subscribers.htm
> Elecraft web page: http://www.elecraft.com
>
>
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>

Nick Waterman

Re: SSB Power

Don Wilhelm wrote:
> This can be observed easily on an oscilloscope - first observe the
> amplitude of your power setting in CW, and then switch to SSB. If
> the voice peaks come up to the same amplitude as you observed for the
> CW signal, you are achieving that same level of PEP (peak envelope
> power). The average power will be considerably less than the PEP
> power for SSB.

I'm guessing, if you can produce a single nice clean sine wave on an
audio frequency signal generator, sending a clean sine in SSB ought to
be approximately equivalent to sending a single carrier in CW?

--
"Nosey" Nick Waterman, G7RZQ, K2 #5209.
use Std::Disclaimer; [hidden email]
You never find the what you want, until you replace it.
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Don Wilhelm-3

RE: SSB Power

Nick,

No need to guess, that certainly is true - a single audio tone transmitted
without a carrier present will produce a single signal at a frequency of the
carrier + or - the tone pitch (depends on the sideband). The amplitude will
of course depend on how strong the audio signal is, but it could develop as
much as the CW signal before driving the signal into a non-linear region
(that non-linear maximum will depend on the transmitter design - I do not
believe that is any need for concern on the K2)

73,
Don W3FPR

> -----Original Message-----
>
> Don Wilhelm wrote:
> > This can be observed easily on an oscilloscope - first observe the
> > amplitude of your power setting in CW, and then switch to SSB. If
> > the voice peaks come up to the same amplitude as you observed for the
> > CW signal, you are achieving that same level of PEP (peak envelope
> > power). The average power will be considerably less than the PEP
> > power for SSB.
>
> I'm guessing, if you can produce a single nice clean sine wave on an
> audio frequency signal generator, sending a clean sine in SSB ought to
> be approximately equivalent to sending a single carrier in CW?
>
> --
> "Nosey" Nick Waterman, G7RZQ, K2 #5209.
> use Std::Disclaimer; [hidden email]
> You never find the what you want, until you replace it.
>

Ron D'Eau Claire-2

RE: SSB Power

Don, W3FPR wrote:

No need to guess, that certainly is true - a single audio tone transmitted
without a carrier present will produce a single signal at a frequency of the
carrier + or - the tone pitch (depends on the sideband). The amplitude will
of course depend on how strong the audio signal is, but it could develop as
much as the CW signal before driving the signal into a non-linear region
(that non-linear maximum will depend on the transmitter design - I do not
believe that is any need for concern on the K2)

--------------------------------

A few of the 1960's-vintage SSB rig designs used exactly this method of
producing CW. It quickly fell from favor because the suppression of the
opposite sideband and even the carrier suppression often was not good enough
to avoid unnecessary and perhaps illegal levels of spurious signals. Some
SSB rigs had no more than 30 dB of opposite sideband suppression, perhaps
less. That's about five S-units, so an S-9 signal would have a image signal
at about S-4 somewhere between 1 and 2 kHz away (twice the modulating
frequency).

Ron AC7AC

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Matt Osborn

Re: SSB Power

In reply to this post by Matt Osborn

On Fri, 10 Feb 2006 18:52:03 -0600, Matt Osborn <[hidden email]>
wrote:

>I'm not certain I know how to understand what it is I'm measuring. In
>my mind, I think much the 20 watts RF out of a CW signal is actually
>carrier and of not much use. When in SSB, I want to think that I can
>still put out the 20 watts, only now all concentrated in one sideband.
>
>Why does the power meter fail to show the 20 watts?

Thanks for the all the replies. One of the difficulties of any new
venture is comprehending what it is that we see.

What I've learned here is that the V50 RF finals have a dynamic range
of 20 watts and will supply what the input signal demands up to 20
watts. The CW signal, due to its increased intensity, demands more
average power when compared to an SSB signal.

Using the Elecraft two tone generator, I found that the 1900hz tone
demands more power than the 700hz tone and when both tones are on, the
demand approaches that of the CW signal and is confirmed by the power
meter.

Thanks again for the education.
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