Signals over S8?

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Over the last while I noticed signals over S8 tend to spread out at the bottom on the panadapter and show images out past the TX band pass on the waterfall. If they go near S10 then they lock really bad. I have noticed this when talking to stations I know are transmitting very clean. When their signal falls below say, S7 they clean up. Their audio does not change, no distortion.

Dave W2OX and I have talked about this and we still do not know what to take from this yet.
I wonder if this is an under the hood fix? It looks like an overload.
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Bill -VA3WTB

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Posted 2 years ago

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Tim - W4TME, Customer Experience Manager

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It isn't overload.  It is almost impossible to overload the 6000 and if you did, that is not what it would look like; it would be flat-topped signals.
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What you are seeing may be normal.

S9  sigs and above allow you to see the normal IMD products (and other ugly stuff) that come form the transmitter. Sigs below S9 or so, keep the normal crud near or below the noise floor on the band so you do not see it.

Start with an S9 + 10 dB sig

Spurious sigs  40db  below peak (from a fairly clean transmitter)  still leaves an S4 sig if I have my math right.
I have seen considerably worse sigs and signals that are much better than this.
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Bill -VA3WTB

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I am asking this this because Dave W2OX and I were talking and we both looked bad,,,above S9.
but we were transmitting clean this I know,,if we went to S8 we cleaned up,,,so what I'm hearing then is we were both very dirty as the signals got stronger. I would have thought if our Tx was clean it would look clean even when signals are strong.
I hope Steve or someone at Flex could help me understand  what I'm seeing.
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Bill -VA3WTB

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Ken - NM9P

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Official Response
Let's say that your noise floor is S4.
That gives you 5 S-Units to S9.
Each S-Unit = 6dB.
5 x 6 = 30 .

S9 is 30 dB above your noise floor.

If your rig/amp has intermod products that are 30 dB down from your peak signal, then at S9 they would just begin to show above the noise floor, showing up as the beginning of shelves on each side of the TX passband.

I'd you go up to S9 plus 10 dB (there is no such thing as S10) then the shelves on the sides of the TX skirts will begin to show increasingly wider.

As the noise floor, signal strength, or intermodal distortion products change, then the position, strength, and width of the skirts will change according to the numbers in the formula.

If the station is S9+30 dB, or even higher, then the bottom of the signal could look very broad, indeed.

Most modern amps are in the 35-45 dB range. Some are worse. Some are below 30! And if the amp is not tuned properly, or is overdriven, the numbers go downhill quite rapidly.

The thing about the Flex is that you can SEE it.

This is why many are salivating over Adaptive Pre-Distortion, which has been shown in some cases to exceed 50 dB down or more.

Ken - NM9P
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Ken K7YR

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I am not up the the Canadian technical standards, here is a copy of FCC emission standards:

§97.307   Emission standards.

(a) No amateur station transmission shall occupy more bandwidth than necessary for the information rate and emission type being transmitted, in accordance with good amateur practice.

(b) Emissions resulting from modulation must be confined to the band or segment available to the control operator. Emissions outside the necessary bandwidth must not cause splatter or keyclick interference to operations on adjacent frequencies.

(c) All spurious emissions from a station transmitter must be reduced to the greatest extent practicable. If any spurious emission, including chassis or power line radiation, causes harmful interference to the reception of another radio station, the licensee of the interfering amateur station is required to take steps to eliminate the interference, in accordance with good engineering practice.

(d) For transmitters installed after January 1, 2003, the mean power of any spurious emission from a station transmitter or external RF power amplifier transmitting on a frequency below 30 MHz must be at least 43 dB below the mean power of the fundamental emission. For transmitters installed on or before January 1, 2003, the mean power of any spurious emission from a station transmitter or external RF power amplifier transmitting on a frequency below 30 MHz must not exceed 50 mW and must be at least 40 dB below the mean power of the fundamental emission. For a transmitter of mean power less than 5 W installed on or before January 1, 2003, the attenuation must be at least 30 dB. A transmitter built before April 15, 1977, or first marketed before January 1, 1978, is exempt from this requirement.


While the FCC quotes -43 db below the mean power level, I find a realistic nominal value seems to be a little less than that..... Say -40 db.  For this discussion lets forget S meter readings and view DBm readings.

A S9+10 DBm reading is about -63 DBm.  -40 DBm would be about -103 DB.  From the peak RF pedestal, say its 2.7 KHz wide, the pattern should descend vertically on both sides to -103 DBm and then it will widen out some what.  Note than a reference signal of -103 DBm is still an S-4 meter reading and at my location on 75 meters my noise floor is usually -112 DBm.  An S-4 signal blows up the headset or speakers. 

Note that this typical S-9 + 10 DBm signal still meets FCC standards. {almost]

One further hint, trying to view the bouncy-bouncy SSB RF pedestal is difficult.  What I do  is bring up an MS Word page and "Print Screen" the Flex "Picture" to the MS Word to analyze a frozen point in time.

Hope this is not too wordy.  The Flex machines are close to professional spectrum analysers, we have a fine tool here.


BTW: Only use the power needed for communications.  I find that on 75 meters I can run 5 watts and most folks don't see the difference between QRP and 1KW [ 5 watts = 39 DBm, 1,000 watts = 60 DBm a 20 DBm delta.

Enjoy your Flex

K7YR  Ken



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John - K3MA

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Be sure to understand Harmonic emissions vs Spurious emissions.

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