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Posted Wednesday, August 10, 2011 5:26 AM
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Hello everyone,

I have perused the "Subjects" and without reading every one I have not found a related subject title, what I would like to ask is what level of noise do others get (attempting to ascertain if mine is normal).

My "S Meter" is showing S3 on 6m without any antenna plugged in, just on a dummy load.
The 3k Panadapter is displaying -110 dBm of white noise.
Also as a guide it shows -113dBm on 40m the best band is 10m with -133dBm.

I am using a linear type PSU.

Having been historically (42yrs on the air) involved with "Normal" HF transceivers which show S0 on their S meters with dummy load plugged into the Ant socket this does not look OK to me.

Your comments would be appreciated.

Terry G4AFS.
Post #4713
Posted Wednesday, August 10, 2011 10:13 PM
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Terry,

I've only had my 3k on the air for a couple of days but on 6m with no signal except for normal local noise my panadapter is sitting on -145 and my S-meter is just over half an S-unit. If I put my antenna switch to the ground position the meter is sitting all the way at the bottom and the panadapter is just below the -150 mark.

You said you have a linear power supply but are there any other electronic items around the shack with the little wall wart power supplies or anything else with a cheap switching supply like a cable modem or router? It could be coming from anywhere, the only way to find it is to start unplugging things.

Good luck!

Kerry, WD5ABC
Post #4716
Posted Monday, August 22, 2011 8:26 AM
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The text bellow is translated automatically from dutch into English.


S-meter indication PowerSDR

A good S-meter is not S0 to indicate if no antenna is connected.

Few devices S0 to give when no antenna is connected.
That would be technically not correct.
Noise is a "field strength".

Our SDRs have professional measuring properties.
PowerSDR measures the sum of the spectral power within the set range.
Thus, the S-meter is noticeably when the bandwidth is set for example 25 Hz.

The relationship between bandwidth and noise power can be calculated using the following formula:

The difference in noise power = 10 x log (bandwidth 1 / 2 bandwidth)

An example:

The noise power at a bandwidth of 5.0 kHz -119 dBm
The difference in noise power at a bandwidth of 500 Hz, then 10 x log (5000 Hz / 500 Hz) => 10 dB

The appointment is then -129 dBm is

The narrowest bandwidth is set to 25 Hz, which is still 3 dB more noise power that appears when the spectrum display PowerSDR.
The spectrum display measurement with the smallest possible filter element of the DSP, which is 10 Hz (for a sweep of 48 kHz).

Conclusion.

The S-meter PowerSDR:

1. should not fall back to "0"
2. shows the spectral sum to within the bandwidth is set.
Post #4750
Posted Tuesday, August 23, 2011 12:09 PM
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Terry,

As you noted as you lower the Bandwidth the S meter will go down,  but never to "0"  ..  SDRs do not sample the S meter the same as conventional radios.   Maybe this KC article helps.

http://kc.flexradio.com/KnowledgebaseArticle50319.aspx

73,

Dudley

FlexRadio Systems Support
512-535-4713, Option 2
http://helpdesk.flexradio.com

Post #4754
Posted Saturday, September 10, 2011 10:24 PM
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Terry

I have not yet purchased a flex as I am very much looking at going this route soon.

Can I make a couple of other suggestions as too the noise you are seeing:

check the computer power supply, contrary to what most people think there are many a crappy noise producing computer power supplies being used and installed in a lot of off the self computers, I wont name any manufacture names but I have seen 3 of the very common names use some cheap power supplies that are very offending!

I have been servicing computers for about 18 years , and work on many here at home as a part time supplement and means of supporting my amateur hobbies, wel I have had quite a few computers on the bench and listening to the HF rig have seen the noise come up 1-5 s units with some of these power supplies. I would look there first, do you have another computer or laptop available you can load up PowerSDR on and see if you still have the same noise problem?

Also is your computer really grounded? have seen users use a plug adapter that doesn't have the ground side of the power cord connected to anything. That can be a big problem.

Have you tried grounding your computer case if a desktop and also the flex radio to the same ground point ( DO NOT USE THE SAME WIRE TO DO SO)
also the ground wire should be of a heavy gauge wire as well. On the computer loosen a screw that holds the power supply or a case side panel on and use a wire ring connecter under the screw.

If a laptop is being used try this simple test, make sure it is charged up well and then disconnect the AC charger from it's AC source (unplug the AC end of it) not just the plug that goes into the laptop, could be a noisy power adapter and this will help narrow that down.

How about florescent lights in the shack? they can be a problem as well at times.

I hope you find the problem,

If it's a desktop computer and you find that the power supply is the culprit post again and I can help make a recommendation on a PSU replacement if you'd like

Also as mentioned d check wall warts there know for having bad shielding and causing noise as well.


Rick
Post #4845
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