[Hackrf-dev] power

[Cinaed Simson]

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
>>
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> 
> .
>