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noise to signal ratio

I keep seeing -dbm from you but I dont have -dbm on my sig gen.
I only have db.

Are you trying to tell me they are the same?

I bet they are not and that is not what your telling me. Plus when I set my gen. to 50 i get one signal strength and if I set it to 67 I get a stronger signal strength.
This is not working for me. somehow I must not be understanding and/or not explaining right. Here is a picture of my gen.
 

Attachments

I could not find any information on the E-2000 but I did find lots of info on the E-200D.

Everything you need to know about setting the output level is in the operators manual.

I think you are overlooking some details associated with the terminology.
0dbm is 1 milliwatt. (0.001 watts) and that is 223 mv (0.223 v)into 50 ohms.
Anything less than 0dbm is negative. (-)
So -67 dbm would be less signal than -50 dbm.
And besides that generator is not capable of achieving the ouput level you have indicated in previous posts.
 
Thank you Radioman! You are correct that it is a 200D. I guess I need some new Glasses.

I will do some more reading on this in the operators manual. Thanks for your time with this. I'm thinking I just might need to upgrade. I did DL the program Robb was using. I'll have to do some more reading on it too.

Jerry....
 
You should do a test to make certain that you get the expected results with this generator.
You need to know if it is shielded well enough and if the common mode currents will be small enough so as not to interfere with the desired results.
You can make this check by hooking it to a radio and then turning on all attenuation switches for maxiumum attenuation.
There should be no discernable signal present; If there is it could interfere with the expected results.
It appears that the generator has a least 96 db attenuation in the attenuator; That should be enough to be well below the sensitvity capabilities of the radio.
If you can hear the modulated carrier from the generator then that means the generator is not shielded well enough for this purpose or it has common mode currents on the cable between the generator and the radio.
You can eliminate the common mode currents with the appropiate ferrite core.
If it passes the test then you won't need to do anything else but establish -67 dbm signal level with the proper combination of the attenuator switches and the FINE ATTENUATOR control.
With all attenuation off (all ATTENUATOR switches in the "OUT" position) and the "SET LEVEL" established (meter pointer to the red 0 on the top scale of the meter ) with the FINE ATTENUATOR control, the ouput is supposed to be 100 millivolts, which is -7dbm.
To achieve the level of -67 dbm you will need to add 60 db of attenuation; Take 3 of the 20 db switches and move them to the "IN" position.
(You have just added 60 db of attenuation to the already level of -7dbm for a total of -67 dbm; Which is right on target)
If the generator is shielded well enough and the common mode currents are low enough this will give you a fairly accurate signal level.


The following is from the operators manual:

SETTING THE SIGNAL LEVEL

1. Be sure the output is terminated in a 50 ohm load.
2. Set the MODULATION switch (15) to the CW position.
3. Set the METER switch (2) to the CARRIER position.
4. Determine the amount of attenuation required to produce the desire output level .
The desire output leve may be in millivolts, microvolts, or db, but must be converted to db to correspond witht the labelling on the controls.
In this unit 0 db = 100 millivolts into a 50 ohm load.
5. Place as many ATTENUATOR selectors (10) in the position as required to come with within 0 to +5 db of the desire total attenuation.
All the other ATTENUATOR selectors (10) must be in the OUT position.
6. Set the FINE ATTENUATOR control (9) for the additional attenuation, as indicated on the meter (3) (this should always be in the 0 to -5 db region of the meter scal).
The total of all ATTENUATOR selectors and the meter reading equals the total attenuation below the 0 db (100 millivolt) reference level.


NOTE:
A. For greater accuracy, use an unmodulated signal level (MODULATION switch in CW position).
B. If the output is not terminated in 50 ohms, the output level is not calibrated.
However, the meter and ATTENUATOR selectors still provide indication of relatviley higher or lower level.
 
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Thanks for the descriptive info Radioman!
I did the test as you advised. I put all the attenuator switches in the IN position, Put the fine control on "0" and with 30% modulation and the power switch on "INT" Also with the gen hooked to a radio I'm am hearing the signal.

Now if I turn the fine carrier adjustment down to -10 then the signal goes away.

So what do you think? Not shielded enough? Maybe I should get another gen. as I dont think this one is very stable as it floats off frequency a touch now and then.

BTW, I did DL the program Robb posted up and did the best I could with it. The radio has got to be better now but I still want it perfect if I can get it there. hi.
 
longhaireddwb said:
OK, Now that I finally got home. Its tough driving truck and doing things at home.

I've had some time to look at the chart and I'm just not getting it. I think its just above what I know. I guess I need someone to help me to understand the ratio of DB to DBM so I can figure out what DB I need to set my sig. gen. to to do a RX alignment. Sense it only has DB settings.
OR
Just tell me the setting I need to put my sig. gen. on in DB to do this alignment.
1uv is = to ? db
and
100uv is = to ? db
It sure would be nice to get this last stage of the alignment done on my rig before I go back on the road Sat.

I will try the way that was mentioned first then DL the program that Robb showed and do it again. I figure both ways will help me to learn better.

Thanks again for all the help with this.
Jerry...

BTW, I've been going with 50db on my gen. to set S-9. Please tell me this is right or not.
Thanks
Click to expand...

Sorry about the half explanation-

dB is completely relative term, so that if something is twice something else (like voltage), it is 3dB greater. This is because the common log of 2 is 0.3. Named after Bell, it is called a Bell. Not too clean, so they came up with dB (decibel...or 1/10th of a Bell), so 2 X greater is 3dB greater. Common log of 10 is 1, so in dB, it is 10dB. It is useful though. Think of 1 and 1000. That covers the ratio between 1uV and 1mV. The common log of 1000 is 3, so in dB, 1000 is 30dB greater than 1dB. Dynamic range of the front end of these radios are spec'd in dB. Logs are added.

Now dBm is a reference to a specific power level...1mW. 0dBW is 1 watt. It takes 30 dBm to get to 0dBw. One mW (0dBm) is a measure of power, which is developed with a voltage across a resistance. In this case, 50 ohms.

The uV to dBm table is equating the voltage (real microvolts) to dBm (10*log(10) of mW), based on 50 ohm loads. Since your signal gen is spec'd to work into 50 ohm systems, it uses dBm (I think) on the controls. To get the equivalent uV (the sensitivity based on your radio), you can use the table.

If you reduce the signal level by 10dB on the control, then it is now 10 times less (in power), if you change by 20dB, the power is now 100 times less, and 30dB change equates to a real output reduction of 1/1000th of where you started. The change in voltage for a given power change depends on the resistance you are working into.
 
Last edited:
KG6YGE said:
Sorry about the half explanation-

dB is completely relative term, so that if something is twice something else (like voltage), it is 3dB greater. This is because the common log of 2 is 0.3. Named after Bell, it is called a Bell. Not too clean, so they came up with dB (decibel...or 10 times a Bell), so 2 X greater is 3dB greater. Common log of 10 is 1, so in dB, it is 10dB. It is useful though. Think of 1 and 1000. That covers the ratio between 1uV and 1mV. The common log of 1000 is 3, so in dB, 1000 is 30dB greater than 1dB. Dynamic range of the front end of these radios are spec'd in dB. Logs are added.

Now dBm is a reference to a specific power level...1mW. 0dBW is 1 watt. It takes 30 dBm to get to 0dBw. One mW (0dBm) is a measure of power, which is developed with a voltage across a resistance. In this case, 50 ohms.

The uV to dBm table is equating the voltage (real microvolts) to dBm (10*log(10) of mW), based on 50 ohm loads. Since your signal gen is spec'd to work into 50 ohm systems, it uses dBm (I think) on the controls. To get the equivalent uV (the sensitivity based on your radio), you can use the table.

If you reduce the signal level by 10dB on the control, then it is now 10 times less (in uV), if you change by 20dB, the voltage is now 100 times less, and 30dB change equates to a real output reduction of 1/1000th of where you started.
Click to expand...

Typical RF sig gens behave as below:

A 3dB change is a change of a factor of about 1.41 in voltage on a typical signal generator (not a change factor of 2)
A 10dB change is a change of a factor of about 3.16 in voltage (not 10)
A 20dB change is a change of a factor of 10 in voltage (not 100).
A 30dB change is a change of a factor of about 31.6 in voltage (not 1000).
 
Last edited:
First off a dB or decibel is one tenth of a Bell, not ten times a Bell. The metric prefix deci means 1/10 while the prefix deca means times 10.

Next, do not confuse power and voltage when talking dB. When you double power you increase by 3 dB but when you double voltage you need to increase it by 6 dB thus the 1.41 versus 2.0 times error above. When halving the output from a signal generator you reduce the output by 6 dB as the generator references voltage and not power.


dB chart voltage power table conversion sound pressure sound intensity decibel voltage level levels ratio dbu dBA dBm absolute relative acoustic measurement volts watts and pascals database - sengpielaudio
 
Captain Kilowatt said:
First off a dB or decibel is one tenth of a Bell, not ten times a Bell. The metric prefix deci means 1/10 while the prefix deca means times 10.

Next, do not confuse power and voltage when talking dB. When you double power you increase by 3 dB but when you double voltage you need to increase it by 6 dB thus the 1.41 versus 2.0 times error above. When halving the output from a signal generator you reduce the output by 6 dB as the generator references voltage and not power.


dB chart voltage power table conversion sound pressure sound intensity decibel voltage level levels ratio dbu dBA dBm absolute relative acoustic measurement volts watts and pascals database - sengpielaudio
Click to expand...

Yes, to clear up any confusion for anyone reading these last few posts, the dB scale on a typical RF signal generator attenuator is usually referenced to a power ratio so a 20dB change in level means a change by a factor of 10 (or 0.1) in voltage. (and not a voltage change factor of 100 as KG6YGE claims)

Maybe KG6YGE doesn't realise this?
 
Last edited:
longhaireddwb said:
Thanks for the descriptive info Radioman!
I did the test as you advised. I put all the attenuator switches in the IN position, Put the fine control on "0" and with 30% modulation and the power switch on "INT" Also with the gen hooked to a radio I'm am hearing the signal.

Now if I turn the fine carrier adjustment down to -10 then the signal goes away.

So what do you think? Not shielded enough? Maybe I should get another gen. as I dont think this one is very stable as it floats off frequency a touch now and then.

BTW, I did DL the program Robb posted up and did the best I could with it. The radio has got to be better now but I still want it perfect if I can get it there. hi.
Click to expand...

You might need to confirm proper action of the attenuators.
If you do no know the complete history of this generator (did someone inadvertantly transmitt into it and over-dissapate one of the resistors) then this is something that I myself would do so I would have more confidence with the end result.
This unit is aged so switch contacts could be an issue.
I would generate a S9 signal and then compare signal level drops between the 4 "20 db" attenuator sections.
Then move on to the "10 db" and the "6 db" sections and see if the drops associated with those sections are consistent with their numbers.
While you are doing this you will also be characterizing the Smeter on the radio.
Let us know the results.
It is normal for a non commercial generator to drift some.
It might not be possible to do the SINAD adjustment while in the sideband mode on the radio.
What mode have been in while trying to use the generator with the radio...... I guess I have assumed that you were in AM mode.
Thank you
 
Last edited:
Wow, Now my brain really hurts!
I'll have to read that stuff a few times and hope a tiny bit sinks in.

I will try the difference between all the 20 and 10 db attenuator setting on a radio and see what happens. I can also clean up all the switch contacts on it just to be sure they aren't causing any problems. I know I never keyed up into this generator but that don't mean someone in the last 20 or 40 years never did. Or how ever old this thing is. It is in great looking shape. As I said before I found a mod on-line that made an output for a frequency counter to be connected without attenuation and not take away any of the power going out so as not to mess with the full output. This has been very handy.

Thanks to all for chiming in on this and helping to explain to a RF dummy. I'm doing the best I can to figure this stuff out and want everything to be right on the rest of the radios I might tune up as I buy and fix a few now days and can never keep just one radio. I like to change a lot.

BTW, I was in the AM mode on the radio. And in the INT mode on the generator. There is a CW mode on the Generator too but I never tried it.

For now its back on the road at 2am in the morning and I'll be back next weekend.

Jerry...
 
longhaireddwb said:
Wow, Now my brain really hurts!
I'll have to read that stuff a few times and hope a tiny bit sinks in.

I will try the difference between all the 20 and 10 db attenuator setting on a radio and see what happens. I can also clean up all the switch contacts on it just to be sure they aren't causing any problems. I know I never keyed up into this generator but that don't mean someone in the last 20 or 40 years never did. Or how ever old this thing is. It is in great looking shape. As I said before I found a mod on-line that made an output for a frequency counter to be connected without attenuation and not take away any of the power going out so as not to mess with the full output. This has been very handy.

Thanks to all for chiming in on this and helping to explain to a RF dummy. I'm doing the best I can to figure this stuff out and want everything to be right on the rest of the radios I might tune up as I buy and fix a few now days and can never keep just one radio. I like to change a lot.

BTW, I was in the AM mode on the radio. And in the INT mode on the generator. There is a CW mode on the Generator too but I never tried it.

For now its back on the road at 2am in the morning and I'll be back next weekend.

Jerry...
Click to expand...


The CW mode is what you use to establish the "SET LEVEL", after you have done that then you go to INT mode and turn the modulation level set knob to get the desire percentage of modulation.
According to the book if you have the modulation set at a high level and you try to set the rf level to the reference mark (SET LEVEL) with the generator in the INT mode it can iterfere with accurate setting of the level.
Any way, this is how the book wants you to do it:
CW
RF FINE to set "0" level
And then INT if you need a modulated carrier.
And then you set the percentage of modulation with the "MOD LEVEL" knob and off you go.
If you have the radio in SSB mode you would probably want to use the CW mode on the generator so the modulated carrier does not interfere with the beat note.
Well be careful out there on the road.
 
I knocked up a quick and dirty Windows App to show how I think your generator operates.

I've uploaded it to youtube here:

B&K Signal Generator Level Control - YouTube


If the link above doesn't work then search for:

B&K signal generator

on youtube to find it under my username of G0HZU


Note that S9 on a signal meter on the HF bands is -73dBm which is 50uV rms into a 50 Ohm load.

A lot of signal generators display the voltage level in EMF and S9 is 100uV EMF and also a lot of service manuals quote S9 as 100uV. But this is 100uV EMF and

your sig gen is calibrated in Vrms into a 50 Ohm load.

So you need to select 50uV for S9 (-73dBm) and you can get this with the attenuation set to 66dB with the meter cal set to 0dB with the fine attenuator

Hope this helps :)
 

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