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New 1000khz AM bandwidth for CB? The entire CB band taken up by one guy.

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k9rzz

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Stick your microphone in a vacuum cleaner hose. See how wide you become. (not that I would really know)
 

jdobbs2001

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I found out what it was. its a mode called SSAM (Spread Spectrum Amplitude Modulation) Its a Jam resistant mode. You need another Rig that supports SSAM in order to leverage it.
 

LtDoc

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Oh lord, another CB myth is born! What possible use would something like this be? 'Jam-proof'? Give me a break. The 'catch' to that is that everyone else is being interfered with, right? Don't tell people you are doing this stuff, you'll get shot.
- 'Doc
 

Token

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How is this possible? I never have seen the whole CB band taken up by one transmitter. Anyhow the video will show you the spectrum occupied by one guy. Crazy.

I wonder how far out it goes.
I am betting you are a relatively new user of SDR or wideband spectrum monitors on HF specifically. What you are seeing is not all that unusual, and no it is not “Spread Spectrum AM” (whatever that is).

There is a possibility that the signal is strong enough to be causing clipping in you’re A/D. This can have the effect of widening the signal to cover the entire sampling bandwidth you are currently set for. The next time you see something like this throw some attenuation in the front end and see if it changes the shape any. Or this guy might really be that wide, or it might be a combination of the two. Note the stations peak power, then note the power of the wide spectrum, it is more than 40 dB down even during the time periods when it is worst.

T!
 

jdobbs2001

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I am betting you are a relatively new user of SDR or wideband spectrum monitors on HF specifically. What you are seeing is not all that unusual, and no it is not “Spread Spectrum AM” (whatever that is).

There is a possibility that the signal is strong enough to be causing clipping in you’re A/D. This can have the effect of widening the signal to cover the entire sampling bandwidth you are currently set for. The next time you see something like this throw some attenuation in the front end and see if it changes the shape any. Or this guy might really be that wide, or it might be a combination of the two. Note the stations peak power, then note the power of the wide spectrum, it is more than 40 dB down even during the time periods when it is worst.

T!
The guy was harping on the radio how he was able to transmit on the whole CB band, and how hey could key over everyone etc.. He still transmits but rarely uses the wide mode.

A friend with an IC-7800 would hear the whole mess and see it on his scope.


The clipping level on my SDR is +4 Dbm yeah its a crazy high number. The receiver has an ADC clip warning that would go on if that happens, which I have yet to see the warning come up. its a tough receiver.
 

Token

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The guy was harping on the radio how he was able to transmit on the whole CB band, and how hey could key over everyone etc.. He still transmits but rarely uses the wide mode.

A friend with an IC-7800 would hear the whole mess and see it on his scope.


The clipping level on my SDR is +4 Dbm yeah its a crazy high number. The receiver has an ADC clip warning that would go on if that happens, which I have yet to see the warning come up. its a tough receiver.
I have heard many people claim to be able cover the whole CB band, and if you are close enough or the conditions are right then they typically can indeed do it. I have seen guys who’s signal was honestly a MHz or more wide. That does not change what I said to note. Note his carrier level to the power level 200 kHz away. If it was honestly some kind of spread spectrum thing I do not think you would have greater than 40 dB delta there. This appears to be simple over modulation, possibly, just maybe, combined with your receiver or software smearing the display. Note that is not a jab at your receiver, every SDR will do it at some point, just like every traditional receiver can be overloaded at some point.

I think you mean the clipping level of your SDR is -8 dBm (you do have the FDM-S2, don’t you)? Almost every decent DDC SDR I have seen or used has a clipping indication, either in hardware or in software, and on every SDR I have used I have seen, under the right conditions and if I used it long enough, what looks like clipping in the ADC and not had the clipping light lit. Was this honestly clipping or not? I can’t say, but I can say it presented the same or similar visual results as clipping.

The important take away here is not if you are indeed clipping or not under these conditions, but rather to remember that artifacting can impact how you perceive what a signal is doing. Be it moire in the display software, or imaging in the SDR, or any one of a dozen other things.

The next time you see something like this happening tune the center frequency of the offending signal outside your DDC window. Not just your zoomed window, but the DDC bandwidth. If the guy is on say 27025 kHz put the bottom edge of your 1 MHz (example) DDC window at about 27100 kHz. If the guy is honestly wide enough to cover the band you should still see him when he keys, if some of the issue rest in the SDR then this should greatly reduce those tendencies.

Again, keep in mind I am not saying you are not seeing what you think you are seeing, it might very well be just as you see it, I am only saying that there are easy ways to confirm if it is “real” or not and that there are also ways to get sucked into thinking something is there that is not.

T!
 

jdobbs2001

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+4dbm with the attenuator, -8dbm with it off. I used both settings to see. As I said someone with an IC-7800 was hearing him push up the floor across the band, it was wiping out other stations other CB channels. The first thing I did was call and saw if he can see what I see on a different piece of equipment.

This guy was running a big *** amplifier to push that hard. but he sounded like **** though, terrible modulation.
 

Token

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The clipping level on my SDR is +4 Dbm yeah its a crazy high number. The receiver has an ADC clip warning that would go on if that happens, which I have yet to see the warning come up. its a tough receiver.
I think you mean the clipping level of your SDR is -8 dBm (you do have the FDM-S2, don’t you)?
+4dbm with the attenuator, -8dbm with it off. I used both settings to see.
I believe the more-or-less standard is to quote the clipping value without preamplifier or attenuator, or to include the fact that such stages were engaged. That is why the maker of your receiver advertises it as -8 dBm on their web page, and not at +4 dBm, and that is why I asked if it was -8 dBm, to make sure I understood which receiver you had. Otherwise the “best” number would go to whatever manufacturer was willing to install the largest attenuator value, for example someone could build a crap DDC receiver with clipping at -40 dBm, install a selectable 70 dB attenuator, and call it a +30 dBm clipping point. And at these low power levels it cost about the same to build a 70 dB pad as it does a 12 dB unit.

Examples would be the Perseus SDR and RF Space devices.

The Perseus advertises a clipping level of -3 dBm with Preamp off (measured levels are along those lines, I have measured -4 dBm on mine), but the radio includes 0, 10, 20, and 30 dB attenuators, so the manufacturer could claim +27 dBm clipping, if they wanted to “fudge” the numbers. At these power levels (+27 dBm is half a Watt) the power is still easy to handle, you just have to spec the parts for the power, and I have no idea if Microtelicom did that or not.

The RFSpace SDR-IQ does not have an attenuator, but does have a couple stages of variable gain, at the RF and the IF levels. The advertised number of -9 dBm clipping is expressed as at “Max Gain”, my measurements show about -11 dBm. Turning down the gain in the RF Gain settings section of the control panel would result in them being able to advertise clipping in excess of +10 dBm, again if they wanted to “fudge” the numbers. The NetSDR does have a front end attenuator and does not advertise a clipping number at all that I can find, however I have measured it as about -5 dBm. Using the selectable 0, 10, 20, and 30 dB attenuators they would be able to claim +25 dBm, if they wanted to just go for numbers and make sure the pads could handle the power.

I have not found an advertised clipping level for the WinRadio G31DDC or G33DDC, however I have measured both of them myself. My G33DDC clips at about -6 dBm, and the radio includes an adjustable attenuator with up to 21 dB of attenuation, so they could claim +15 dBm if they wanted to cook the books.

My point is, all of the SDRs listed above fall in the range of -11 to -3 dBm clipping, unless you add the attenuators, then the spread becomes much wider. Receiver front end attenuator values are, realistically, only hardware performance limitations by choice (do you really want to have to dissipate all that heat if you allow a +50 dBm input level?), not by technology limitations.

This guy was running a big *** amplifier to push that hard. but he sounded like **** though, terrible modulation.
Yes, that was why I said if this was real and did not involve a reaction by your receiver that this was simple over modulation. You find these people on or around 27025 kHz all the time. Some really do have decent modulation, others are simply bad.

T!
 

jdobbs2001

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Gotta get them bird watts up there. Although its all over 1 mhz instead of within 10khz. :) where it would do more good.

The Bird has no idea how wide those watts are :)
 
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