[Hackrf-dev] Low TX power

[Paul Connolly]

It could be acting like a short circuit, and you would see no difference
switching the TX amp on or off. I'm sure it depends on the mode of failure.

IC's U13 & U25 are part number MGA-81563-TR1G one is for RX and the
other is TX. I think U13 is RX and U25 is TX, you should to load up the
schematic in KiCAD and check.
(source:
https://github.com/mossmann/hackrf/blob/master/doc/hardware/hackrf-one-bom.csv
)

Probably best to verify with the hackrf_transfer command as well before
masking the board with aluminium foil, kapton tape and blasting with hot
air.


On 31/01/2015 23:24, Mark Jessop wrote:
> I was using GNURadio Companion, not hackrf_transfer for my tests.
> I experimented with varying all of those parameters, and could not get an
> output any higher than -30dBm.
>
> If the TX amplifier was broken, i would have expected to see a noticeable
> difference when i switched the amp on and off (i.e. RX LNA gain between 0
> and 14dB), as from what I could tell in the schematic doing so would switch
> the amp in and out.
>
> Cheers,
> Mark
>
> On Sun, Feb 1, 2015 at 2:33 AM, Paul Connolly <eeipcy at gmail.com> wrote:
>
>>  Are using -c 127 as an argument for your testing. And -x goes from 0 to
>> 47dB, why stop at 14dB ?
>> $ hackrf_transfer
>> receive -r and receive_wav -w options are mutually exclusive
>> Usage:
>> ... snip ...
>>         [-l gain_db] # RX LNA (IF) gain, 0-40dB, 8dB steps
>>         [-g gain_db] # RX VGA (baseband) gain, 0-62dB, 2dB steps
>> *        [-x gain_db] # TX VGA (IF) gain, 0-47dB, 1dB steps*
>> ... snip ...
>>         [-c amplitude] # CW signal source mode, amplitude 0-127 (DC value
>> to DAC).
>> ... snip ...
>> $
>>
>> From https://github.com/mossmann/hackrf/wiki/HackRF-One#transmit-power
>> you should be seeing about 15dBm that close to 10MHz
>>
>> It could be that you have damaged the TX amplifier, did you have -a 0 in
>> your tests. Because if it is broken then it would probably act like an
>> attenuator.
>>
>> Paul
>>
>>
>> On 31/01/2015 12:43, Mark Jessop wrote:
>>
>> Hi all,
>>
>> Bought a HackRF a few months back, never properly measured the output power
>> on it when I got it unfortunately, but it has certainly dropped at some
>> point in the last few months.
>>
>> I finally got the chance to put it on a spectrum analyzer the other day.
>> Transmitting a single carrier, I'm seeing a maximum of -30dBm output power
>> at 14MHz. Only a few dB difference noticed when turning the RF Gain setting
>> from 0 to 14dBm (This does actually do something, doesn't it?)
>>
>> Any thoughts? I have the facilities to replace QFN components if required...
>>
>> Cheers,
>> Mark VK5QI
>>
>>
>>
>>
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>>
>>
>>
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