Re: LF: Re: Audio transformer test

[Daniele Tincani <danieletincani@yahoo.com>]

Hello LF,

 

recently I performed some quick and dirty measurements on a Bourns LM-NP-1001-B1, using simply a sine wave generator (50 ohms output) and an oscilloscope (10 Mohms input). On the secondary I connected a 15 komhs load resistor (as Clifton labs found that a load impedance of about 10 komhs was ideal for this transformer, see here for details: http://dl.dropbox.com/u/20845911/Bourns%20LM-NP-1001.doc).

My results (quite surprisingly) seemed to show a -3dB point at around 210 kHz and only -0.4 dB @100kHz.

 

Regards

Daniele

Da: Stefan Schäfer <Stefan.Schaefer@iup.uni-heidelberg.de>
A: rsgb_lf_group@blacksheep.org
Inviato: Venerdì 6 Aprile 2012 13:28
Oggetto: Re: LF: Re: Audio transformer test

Hi Clemens,

In my application i use it to decouple my 2 orthogonal VLF loops from the soundcard and do some "matching" of the low output impedance of the loop to the high input impedance of the soundcard. The levels absolute signal levels rised arround 10 dB, so it is an improvement. However the MSKs, especially DHO38 is 10 dB down now since the transformer does not work on such a high frequency. Anyway, my focus is below 9 kHz and the levels from 9...25 kHz are still fair.
There is however not really a S/N improvement and mains hum and all the man made noise in the H field make the loops rather a game instead of a system suitable to detect weak signals from Dreamers. Seems i have to change the location of the loops. The old problem...

73, Stefan/DK7FC


Am 06.04.2012 10:42, schrieb Clemens Paul:
> Hi Stefan,
>
> I have measured exactly this transformer about a year ago for a friend.
> He tried it for a (meanwhile abandoned) soundcard based SDR- TRX project
> for HF and failed due to lack of sensitivity.
> I connected two of these XMFs back to back and measured in a 50 Ohm environment
> with a VNA from 5-20kHz.
> There was plenty of loss,IIRC something *around* 10dB per transformer.
> That's not surprising after you have measured the DC resistance (high!).
> This may or may not be of importance for your application depending on
> your AF level and type of matching (power matching versus voltage matching).
>
> 73
> Clemens
> DL4RAJ
>
>
> ----- Original Message ----- From: "Stefan Schäfer" <Stefan.Schaefer@iup.uni-heidelberg.de>
> To: <rsgb_lf_group@blacksheep.org>
> Sent: Thursday, April 05, 2012 4:21 PM
> Subject: VLF: Audio transformer test
>
>
>> VLF,
>>
>> I just checked the amplitude and frequency respose of the audio transformer i use to decouple my signals between soundcard and antenna. Just a simple test. They are in use in various applications, are cheep and small.
>> Type, Distributor and datasheet: http://www.reichelt.de/Trenntrafos/NFU-1-4/index.html?;ACTION="">
>>
>> Looks they operate down to 5 Hz which is excellent: http://dl.dropbox.com/u/19882028/VLF/Uebertragertest.png
>> Also the wide range looks fine up to 20 kHz: http://dl.dropbox.com/u/19882028/VLF/Uebertragertest_wide.png
>>
>> In the pictures, the upper SL instance is a frequency generator driving the headphone output of the soundcard. The lower instance records signals coming from the Mic input.
>>
>> As a conclusion i found that the transformer is even suitable for ZEVS receiving at 82 Hz.
>>
>> 73, Stefan/DK7FC
>>
>>
>