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Sample DB down mathmatics?

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fineshot1
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Joined: Wed Oct 12, 2005 5:13 am

Sample DB down mathmatics?

Postby fineshot1 » Thu Jun 29, 2017 11:30 am

I have a couple of Bird sampling elements with the BNC output, 30DB and 50DB down.
I am wondering if there is a math calculation online(or anywhere) one can use to get
a possible sample output with an input power(ie:100W) and get the sample output.
Am I assuming incorrectly of thinking 30DB down is about 10% of a given input?
Perhaps there is a chart of this somewhere, maybe?
fineshot1
NJ USA

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AdrianH
Posts: 32
Joined: Fri Mar 16, 2018 12:03 pm
What radios do you own?: Yaesu FT-857, FT-902DM, FT70

Re: Sample DB down mathmatics?

Postby AdrianH » Thu Mar 29, 2018 10:44 am

I realised, (eventually) that this is an old thread, but it may help someone.

I always work out in my head that every 10 dB down in signal reduces the level by 10. So 10 watts in, with 10 dB loss, I would end up with 1 Watt.

But, 20 dB loss is not a reduction by 20 it is a reduction of 10 x 10 or 100 times the original. So that 10 Watts input would now be 0.1 Watt output

Keep going, 30 dB down would be a reduction of 10 x 10 x 10 or a 1,000th of the original signal, 10 watts input would now give me 10 milliWatt.

Keep on going 50 dB reduction means the output is a 100,000'th of the original power so your 100 Watts with 50 dB loss would be a mere 1 milliwatt output level.

Conversely gain acts in the opposite way, Gain of 10 dB would increase the 10 watt signal to 100 Watts, etc.

3 dB increase doubles power, 3 dB loss halves the power.

These are only for power measurements, considering only voltages as in signal generator output levels is different as that as that is a 6 dB change for doubling the voltage.

Adrian

SmokChsr
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Re: Sample DB down mathmatics?

Postby SmokChsr » Thu Apr 05, 2018 6:20 pm

As was said, 30db is 0.1%. After that now you have to determine if the -30db sample is frequency compensated or not and in what size line it's 30db down.

If it's a 43 slug then it's for a 7/8" line section. But be aware that they have many many slugs that were not calibrated for 7/8" line sections.

The easy way to check things out if you have a calibrated tracking generator run that through the line section into a load and read the output and see where the signal ends up.


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