Return loss and effective radiated power

Discussion in 'Radio and Wireless' started by SparksFly, Aug 21, 2021.

1. SparksFly

10
0
Jan 7, 2019
Hello,

I've been thinking about ERP/EIRP and how they're calculated. I see various definitions, but all broadly appear to be;

EIRP = Ptransmitter - Lcable + Gantenna
where P = power, L = loss, G = gain.

That does make some sense, however I have been unable to find any resources that mention the effect of VSWR or return loss. RL is a loss, but they're don't fit into the cable loss parameter (ie insertion loss).

To take an example, say I had a transmitter at 100dBm, an insertion loss of 4dB and an antenna gain of 3dBi then the EIRP would be 99dBm. Say I then tested my antenna and found it was a really bad match at my intended frequency, and 50% of my power was being reflected back into the transmitter. Following the formula above, the EIRP would still be 99dBm, but only half that (96dBm) would actually be "leaving" the antenna.

Does EIRP take into account RL in a way that I've not realised, or is it deliberately not in there?

Thank you!

2. bertusModerator

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766
Nov 8, 2019
Hello,

Have a look at the attached PDF.

Bertus

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3. SparksFly

10
0
Jan 7, 2019
Wow, that's an eye opener. I continue to be amazed at how little I know! That answers everything. Thank you Bertus.

4. bertusModerator

2,033
766
Nov 8, 2019
Hello,

BTW, 100dBm is a huge amount of power ( 10 MegaWatt ).
0 dBm = 1 mili Watt
30 dBm = 1 Watt
60 dBm = 1 Kilo Watt
90 dBm = 1 Mega Watt
Have a look at the power table.

Bertus

Attached Files:

• power_chart_test.pdf
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