100 KµV Meaning

Todd D

New Member
In working through the alignment of a Marantz 120b tuner, I keep running into units I don't understand. If anyone can shed some light on what KµV means, I would appreciate it. I've looked in manuals for several different Marantz tuners, and I can't find an explanation. It's used in several places:

"Set the SG to provide 1 KµV at 90 MHz" (Stereo Separation Alignment)

"Connect FM signal input of 100 KµV (98MHz, 400 Hz 100% Mod.) to the FM ANT terminal and adjust R559 so that the spot does not frame out." (FM Tuning Display Alignment)

Kilo-micro-volts? If so, why would it be called out this way?

I've stumped an electrical engineer, and Google with this question. If anyone has knowledge, please share.
 
perhaps because they didn't want to write "100,000 µV" and the units of microvolts are familiar and comfortable to, and expected by, their intended audience.
I'm speculatin' here. (EDIT: of course, the "k" should be lower case...)

Sort of like capacitors -- we commonly see, e.g., units expressed as microfarads and picofarads, but not often nanofarads. 0.001 µF or 1000 pF, as opposed to 1 nF (e.g.).

But I'm spitballin' here...
 
100000µV is .1 volts. Wouldn't that be the easiest? If that's what they are saying, why call it out in such a round-about way?
 
As I wrote:
and the units of microvolts are familiar and comfortable to, and expected by, their intended audience.

I think (i.e., speculate) that microvolts are the familiar units for radiated energy... dBf might have been a better choice(?)

I gots nothin' else -- so I am not stumpin' for a debate.
 
Your logic may be correct. It's the only conclusion that makes any sense at this point. It's referenced different times, in different manuals, so I know it's not a misprint.
 
As strange as it sounds, this seems to be a thing. I came across this image of a common FM test signal generator, with output in uV log scale from 0.5 to 30k. I'm guessing it's the log scale that made 1k uV seem like a good idea to someone ;)

sound_technology_1000a_fm_alignment_generator.jpg
 
dBf is a power level referenced to one femtowatt.

It allows for easy comparison of the sensitivity with different impedances 50, 75, 300 Ohms and so on, because it is power not voltage.

Radiated RF energy may be described by energy per unit of area or by volts per meter. For example the maximum legal RF strength for a home use (FCC part 15) FM transmitter is 250 microvolts per meter as 3 meters from the transmitting antenna.

Typical FM broadcast band receiver sensitivity for a usable but not necessarily hiss free signal is in the low, single digit, microvolt range. On the other hand depending on local FM RF signal strength a receiver may see a much higher RF level.

Low numbers for maximum sensitivity can be a good thing for weak signals, but the receiver must be designed so that very strong signals do not overload the RF front end of the receiver, resulting in various problems.

An example of dBf and microvolt sensitivity ratings. Note that usable, but not hiss free, sensitivity is 1.8 microvolts or 13.2 dB (they both mean the same thing).

Note the higher signal level needed for 50 dB of quieting (hiss reduction).

upload_2017-8-14_18-43-17.png

In the picture below note that maximum quieting does not happen until a much higher signal level.

upload_2017-8-14_18-46-14.png

Note that is 77 dB at 10 millivolts not microvolts.

It has been common to stay with microvolts since the early days of RF. Those of use that have been involved with RF are familiar with this.
 
It's clear you guys are on the right track. So the question now becomes: How do I make that number useful to me? Im using a Leader LSG-216. The KµV is referring to signal strength, but in a unit I don't know how to use. In the link miscrms00 posted, 73dBf = 1KµV. I'm not sure that gets me any closer to where I want to be.

Thoughts?
 
IIRC your generator specifies its output as dBµV.

upload_2017-8-14_19-37-46.png

1000µVolts (1000 microvolts) is 60 dBµV. This is what you would set as the output of your generator.


And 100,000 µVolts is 100 dBµV. This is what you would set as the output of your generator. However IIRC the maximum output of your generator is 99 dBµV (close enough).

Here is a calculator that will help.

upload_2017-8-14_19-43-31.png

Select voltage.

The input will always be 1 as in 1 microvolt. Enter the level in microvolts (as the output) 1000 for your needs, then click on calculate dB and that will tell you what to set for the output of your generator.

For 100,000 microvolts you would enter 100,000 for output and click calculate dB.

upload_2017-8-14_19-49-21.png

Remember RF means Really Fun.

You have to work with what works with your generator.
 
Thanks for the help! Your answer is exactly what I need, and I appreciate it. There are so few people that are willing to share their knowledge of RF, it is refreshing to find someone who is.

So far, RF hasn't meant really fun... More like RF hard.
 
I appreciate everyone's contribution to this. Hopefully I'm not the only one who benefits from it. This is my first FM alignment, so I know that I'll be back with more questions...
 
The basic relationships are V=IR, and P=IV=V^2/R. For power dB = 10*log(W), for voltage dB = 20*log(V). That seems weird but the square term in the Power equation is the culprit.

I've seen pictures of the front panel of the 216, but only found a manual for the 215. The output is marked dBu, which could be power or voltage, but the 215 manual states this is voltage. I'm assuming the 216 is the same. Taken with the u, that means 0dB = 1uV. And for each 20dB the output will go up by a factor of 10. So, 1KuV (1,000uV) will be 60dBu. 100KuV (100,000uV) would be two more decades or 100dBu.

It shouldn't be needed for your case, but FWIW, 1KuV (1000uV = 1mV) would be 0.001^2 V / 50 Ohms = 20nW or 20,000,000fW. 10*log(20,000,000) = 73dBf. As noted above dBf in this case is dBs of power where 0dB = 1fW or 1E-15W. dBs always have to be relative to something, as they are ratios by definition. 0dB means 1, so its common to normalize to some convenient constant, like 1 fW in this case, or 1uV as in above. It's also why amplifier gain is often specified in dB, as its just the ratio of the output signal level to the input signal level.

Unfortunately I don't know anything specifically about these type of receivers or instruments. I assume since this seems to be a 50 Ohm source, that the above is all true when you are driving into a 50 Ohm load. If the input impedance of the receiver is something else, it gets more complicated.
 
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I assume since this seems to be a 50 Ohm source, that the above is all true when you are driving into a 50 Ohm load. If the input impedance of the receiver is something else, it gets more complicated.

This is true, but all the signal level of 1000 microvolts means is that the receiver is driven into full quieting, but not into overload. This will be close enough. If he wanted to measure the sensitivity and plot a quieting curve he would need to do the math and this is where dBf, if specified, makes this easier.

But even with the mismatch he could still get reasonably close.
 
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