[Hackrf-dev] power

[Roy Harcup]

Hi Cinaed,
Yes, dB is a ratio. However, it is commonly referenced to a mW or a W, which does then give a value. What I was saying is that 30dBm (referenced to one milliwatt) is equivalent to one Watt (1000mW). I did not change the reference. To go from 30dBm to 40dBm, an increase of 10dB is an increase of ten times the power, from 1W to 10W in this case. A further 3dB increase doubles the power to 20W. I did not change the reference. As I said before, I suggest that you read up on dB. By the way, it is incorrect to say dBm = dBW, 0dBW is actually 30dBm.
Best regards
Roy

> On 9Mar, 2016, at 15:27, Cinaed Simson <cinaed.simson at gmail.com> wrote:
> 
> On 03/08/2016 05:42 PM, Roy Harcup wrote:
>> Hi Cinaed,
>> 
>> You really need to read up on dB’s.
>> 
>> 0dBm = 1mW as you have stated;
>> 30dBm = 1W;
>> 40dBm = 10W;
>> 43dBm = 20W, one more dBm will take that to somewhere around 22W (I haven’t done the calculation, I’m working from memory).
> 
> dB is a ratio - ratios have no units.
> 
> That is the ratio of 44mW/1mW = 44W/1W, so
> 
>   10*log_10(44mW/1mW) = 10*log_10(44W/1W)
>   dBm = dBW = 44 dB.
> 
> If you want to change the reference power in the definition of dBm from
> 1 mW to 1 W, then that's a different ballgame.
> 
>> 
>> If you ’smoke’ the RF stage on the HackRF I doubt that you would see anything usable on the output, indeed you could end up with a really bad source of interference.
>> 
> 
> You're probably right - I am trying to do everything I can to keep from
> smoking it.
> 
>> Best regards
>> Roy
>> Formerly G4GGS
>> 
>> 
>>> On 9Mar, 2016, at 09:18, Cinaed Simson <cinaed.simson at gmail.com> wrote:
>>> 
>>> Hi - I'd like to increase the TX power of the HackRF to 50 mW.
>>> 
>>> First, I disable TX.
>>> 
>>> Since the dBm=0, this implies the power output will be on the order of 1
>>> mW.
>>> 
>>> Then I add an external LNA with a gain of 44 dB on the RF band I'm
>>> transmitting on which raises the TX power of the HackRF to 44 mW.
>>> 
>>> The antenna has a gain of 6 dB - the cable and connector losses are on
>>> the order of 1 dB, so the maximum effective power is 49 mW.
>>> 
>>> I'm assuming this independent of the IF gain.
>>> 
>>> So I could smoke the TX amplifier on HackRF and still be able to use the
>>> HackRF to TX at roughly 17 dBm :).
>>> 
>>> -- Cinaed
>>> 
>>> _______________________________________________
>>> HackRF-dev mailing list
>>> HackRF-dev at greatscottgadgets.com
>>> https://pairlist9.pair.net/mailman/listinfo/hackrf-dev
>> 
>> .
>> 
> 
> _______________________________________________
> HackRF-dev mailing list
> HackRF-dev at greatscottgadgets.com <mailto:HackRF-dev at greatscottgadgets.com>
> https://pairlist9.pair.net/mailman/listinfo/hackrf-dev <https://pairlist9.pair.net/mailman/listinfo/hackrf-dev>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <https://pairlist9.pair.net/pipermail/hackrf-dev/attachments/20160309/b2d0c0c4/attachment.html>