50uv singnal source

[p.larner]

I am trying to get a 50uv rf signal level to calibrate my radio s meter,my sig gen has no calibrated outputs,my scope v div is 5millivolt/div min,is there any way to cal my sig gen op for this with what i have,ie a dummy load sig gen+ scope.

[xrunner]

50 uV in a 50 ohm system is going to be -73 dBm. I'm familiar with calibrating S meters, and that will be an S9 (see attached document if you wish).

-73 dBm is a pretty low RF signal, and unless you have a better RF signal gen that is calibrated it will be hard to set up reliably. S meters on radios are not very accurate over the entire scale, i.e. they are not calibrated power meters.

Do you have another "good" shortwave receiver, and can you can tune in a shortwave station such as WWV on 10 MHz for example? If the signal is not fading, you can just note the S meter reading on the good radio, whether it's S1 or S9+30 dB and then switch the antenna to your other radio and make the S meter read the same. Or just use the generator you have and tune it in on the good radio, then switch to the other radio. Since the signal isn't fading much it will be the same RF power level at the terminals. This is not ideal of course, but is about all I can think of with the equipment you have.

[RFDx]

Connect a BNC T-adapter to the input of the scope. The signal generator and a 60dB attenuator (3 x 20dB) go to the remaining ports of the adapter. Adjust the generator for 50mV on the scope. After you're done, connect the attenuator directly to the input of the receiver and the signal generator to the attenuator.

[David Hess]

Connect a BNC T-adapter to the input of the scope. The signal generator and a 60dB attenuator (3 x 20dB) go to the remaining ports of the adapter. Adjust the generator for 50mV on the scope. After you're done, connect the attenuator directly to the input of the receiver and the signal generator to the attenuator.

Exactly, use a higher level signal which can be measured accurately and then add a calibrated attenuator to achieve the desired low level signal.  The attenuator sections can be calibrated at a higher signal level before being used at a lower signal level.

Note that an attenuation of 60dB is reaching the point where the signal will leak around the attenuation so good cables and connectors are needed.  At 80dB I have to use double shielded cables and BNC connectors which are not worn.

[xrunner]

Of course he can do it with additional items, hell I can advise him to get all kinds of parts and things to accomplish the task, but here's what he asked -

... is there any way to cal my sig gen op for this with what i have, ie a dummy load sig gen+ scope.

 

[max-bit]

The solution is a signal generator +(option) decade signal attenuator

[radiolistener]

just use some signal generator with 50Ω output, like Chinese FY6800 or PSG9080.
And use 50Ω attenuator to reduce amplitude to expected level, you can buy these SMA attenuators on aliexpress.

50 uV usually means 50 uVrms, for sine wave it will be 50 * sqrt(2) = 70.71 uVpk * 2 =  141.42 uVpp.

Since Chinese FY6800 or PSG9080 shows unloaded amplitude, you're needs to setup twice higher amplitude to get correct value on the properly loaded output.

So, you're needs to setup 141.42 * 2 = 282.84 uVpp on FY6800. Since it don't allow it, you can use 60 dB attenuator, it will reduce amplitude by 1000 times. So, with 60 dB attenuator you will needs to setup 282.84 * 1000 = 283 mVpp on FY6800.

You can combine two attenuators 40 dB + 20 dB in order to get 60 dB, or combine 30 dB + 30 dB,etc

In order to use SMA attenuators you may need to buy some Chinese BNC-SMA and SMA-BNC adapters.

If you can get BNC attenuators, you can use it without adapters, but it's more hard to find cheap and good quality BNC attenuators.

[antenna]

My procedure using a jun(k)tek DDS generator from amazon..

To do S-meters, I connect a 30dB attenuator to the generator and feed that into a coax switch that is switched to a dummy load.  The unused port (shorted internally) picks up a signal about 60dB lower than what is going through to the dummy load, and that goes into the spectrum analyzer now about 90dB down and the sig gen is adjusted until the SA reads the proper dB level for adjustment. The cable is then disconnected from the SA and connected to the radio that needs calibrating.

My sig gen is one of those dirt cheap ones with no shielding and a noisy squarish-wave sync port on the back that would emit enough RF to be heard in the radio with the RF output switched off, so I had to lift the power leg on that useless sync output chip at the back of the generator and shield the unit with foil tape. 

With the 30dB attenuator and the coax switch acting as another 60dB attenuator, you should have enough attenuation to also test receiver sensitivity.  I tried it once, not sure if I did it right though. If I remember correctly, I believe I had connected the scope (with FFT) to the audio output, set the sig gen to modulate with 1khz @ 30% and turning down the output until the sinad measurement on the scope read 12dB, reconnecting the coax to the SA said the RF was at -124dB.  Not sure if thats the way to do it or not, but that number seems reasonable for that radio (uniden washington)

[aklance]

Get A tinySA ultra it will have everything you need, Sig gen, Spec Analyzer and much more and then get a nanoVNA H4 for everything else. You may also need various connectors and attenuators.

[p.larner]

does the tinysa have a calibrated 50uv output then?or even adjustable?.

[aklance]

Yes the signal generator has very accurate output. Also they are very inexpensive for their capabilities. Same with the nanoVNA.

[JoeRoy]

50 uV in a 50 ohm system is going to be -73 dBm. I'm familiar with calibrating S meters, and that will be an S9 (see attached document if you wish).

There are 2 "S-points for frequencies" tables, for below and above 30 MHz

https://www.giangrandi.org/electronics/radio/smeter.shtml

[xrunner]

There are 2 "S-points for frequencies" tables, for below and above 30 MHz

Uh yea ... if you had looked at the document I uploaded in my post you would have seen it clearly shows the S9 reference for both HF and VHF. 

[tanveerriaz]

search in google "s9 signal generator"