jkowtko
Well-Known Member
Continuing on the topic of antenna distribution systems and what produces "solid" signal strength ...
Our AKG WMS450 receivers measure RF strength on a meter that shows the range of -100 to -60.
I would like to know how that scale compares to the 0db reference for isotropic antennas, and all other gains and losses incurred in an antenna distribution system.
IF these are on the same scale, and the receiver is simply stating that anything stronger than -60 is considered "solid" signal, then my issue is not signal strength so much as antenna placement to always pick up a clear signal. And, if this is the case, then losing 5 or 10, or even 20db of antenna signal strength by extending with coax, pales in comparison to the advantage of placing the antennas in better positions.
But I don't know that it is the case. I couldn't find any info out there that explains it. I did check out the specs from a few of the wireless though ... seems they have different ways of measuring it:
AKG WMS450:
- Rx shows RF bar from -100 to -60, indicates "field strength", no indication of units of measurement. Squelch from -100 to -80.
- Tx is rated at 50mW
Sennheiser G3/100:
- Rx shows RF bar from 10 to 40, specs indicate dbu(micro)V units. Squelch from 0 to 25 dbuV. Sensitivity is 2.5 uV
- Tx is rated at 30mW
Shure SLX:
- No RF meter, specs state receiver sensitivity at –105 dBm. No squelch.
- Tx rated at 30mW
Shure ULX:
- RF meter has no scale. Specs say sensitivity -95 to -30 dBm, -20 dBm recommended. RF sensitivity 1.26 uV. Has squelch but no indication of scale.
- Tx is rated at 20-30 mW
So, my initial take from this information:
1) the scale of the AKG and Shure ULX are the same -- dBm -- and that -100 dBm equates to around 1.25 uV.
2) a "strong" signal should be around -20 dBm, and if that matches the AKG scale, then the AKG RF meter topping out at -60 dBm is a very conservative high end, and the signal should always be much higher than -60.
Is my above interpretation correct? I could be way off ...
And this still doesn't answer the question -- how does antenna signal strength relative to the 0db isotropic calibration point relate to my RF levels. I'm sure it has to do with the Tx transmission power and Tx/Rx distance ... I just don't know the formulas to calculate this ...
Thanks. John
Our AKG WMS450 receivers measure RF strength on a meter that shows the range of -100 to -60.
I would like to know how that scale compares to the 0db reference for isotropic antennas, and all other gains and losses incurred in an antenna distribution system.
IF these are on the same scale, and the receiver is simply stating that anything stronger than -60 is considered "solid" signal, then my issue is not signal strength so much as antenna placement to always pick up a clear signal. And, if this is the case, then losing 5 or 10, or even 20db of antenna signal strength by extending with coax, pales in comparison to the advantage of placing the antennas in better positions.
But I don't know that it is the case. I couldn't find any info out there that explains it. I did check out the specs from a few of the wireless though ... seems they have different ways of measuring it:
AKG WMS450:
- Rx shows RF bar from -100 to -60, indicates "field strength", no indication of units of measurement. Squelch from -100 to -80.
- Tx is rated at 50mW
Sennheiser G3/100:
- Rx shows RF bar from 10 to 40, specs indicate dbu(micro)V units. Squelch from 0 to 25 dbuV. Sensitivity is 2.5 uV
- Tx is rated at 30mW
Shure SLX:
- No RF meter, specs state receiver sensitivity at –105 dBm. No squelch.
- Tx rated at 30mW
Shure ULX:
- RF meter has no scale. Specs say sensitivity -95 to -30 dBm, -20 dBm recommended. RF sensitivity 1.26 uV. Has squelch but no indication of scale.
- Tx is rated at 20-30 mW
So, my initial take from this information:
1) the scale of the AKG and Shure ULX are the same -- dBm -- and that -100 dBm equates to around 1.25 uV.
2) a "strong" signal should be around -20 dBm, and if that matches the AKG scale, then the AKG RF meter topping out at -60 dBm is a very conservative high end, and the signal should always be much higher than -60.
Is my above interpretation correct? I could be way off ...
And this still doesn't answer the question -- how does antenna signal strength relative to the 0db isotropic calibration point relate to my RF levels. I'm sure it has to do with the Tx transmission power and Tx/Rx distance ... I just don't know the formulas to calculate this ...
Thanks. John