Re: measuring uBITX IP3 with FLDIGI

Rod Davis <km6sn@...>

On 05/03/2018 08:05 AM, Gordon Gibby wrote:

​I should try that with the cheap $5 dongles we use locally for sound cards for HF and packet.....I bet they aren't near as nice....


From: <> on behalf of Rod Davis <km6sn@...>
Sent: Thursday, May 3, 2018 11:02 AM
To: BITX20
Subject: [BITX20] measuring uBITX IP3 with FLDIGI

Hi All,

Some time ago I was curious about the quality of embedded sound cards in my old
Dell laptops, so I connected two of them together with audio cables, and ran
FLDIGI on both of them,  in PSK31 mode.That mode shows IP3 information.

I simply used audio-to-audio connections, with no intervening TX and RX. 

I was stunned to see that IP3 was in the -80 dB region! I was impressed
with the quality of the built-in soundcards.

That means it is possible to get a coarse IP3 measurement on a uBITX
using a laptop and a reasonable quality auxiliary receiver, listening to PSK31 from the uBITX.

The measurement would certainly be good enough to give IP3 indications
when adjusting TX RF drive levels, and mic gain, and soundcard output levels.

Be careful not to overload the aux receiver, and turn off the AGC.

Another possibility is to use an audio spectrum analyzer program on the receiving
PC to see the IP3 and IP5 peaks.

Free test equipment!


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