Hello friends
I am building another BITX40, my other with two bands work great but
there are many external boxes to plug togheter...
If you are looking articles for mesurenents of filtres by sound card
in english try :
I have the Spectra and the Gram softwares, bouth work very nice...
For good results build the filter and the input IF amplifier / output
IF amplifier, BFO, 2nd mixer (demodulator) and the audio amplifier...
Remember that if you change the impedance of input or output of the
filter you change the filter caracteristics. A good idea is to adjust
using the real circuit.
I am building my filter using Fahran way... I buy 20 10MHz xtal ... I
make a oscilator circuit and measure the frequency with and withot a
33pF ... now I am assembling others parts...for to analize the
filter...
If you want to build a Noise Generator ... it is easy ... make a RF
amplifier with two estages ending with a broad band bifilar
transformer, in the input you need to test some Zener diodes types
(more power and low voltage give best results) ... gud luck
I will upload two versions of the freeware GRAM spectroanalizer ...
73 from Brazil
PY2OHH Miguel
--- In BITX20@..., "Max" <m_orwell@y...> wrote:
In German Funkamateur was published schematic for hf noise
generator
and described metod of mesurment by using sondcard lf spectogram. I
am sorry that it is again in russian but can be easily translated.
I
couldnt find similar article in english. Schematics are
understandable on its own.
--- In BITX20@..., "vdberghak" <vdberghak@z...> wrote:
Indeed measuring is knowing if the final result is in line with
the
original expectations.
As mentioned before, it can be easily done with the sound card.
At
that
time, I asked for feedback (screenshots of the same method) of
measured
filters to see if my 4,9 MHz filter is about in line with the 10
MHz
version. If some members do this measurement it is possible to
compare
results and find out if it is really a 'lottery'. As I
understand,
most
builders have their filter dimensioned in accordance with the
original
schematic and they all seems to work fine?
OK builders, please download the few kb program, connect your
BITX
to
the sound card, measure the shape of the filter and post the
screendump!
Thanks in advance,
Chris.
Without measuring to get
good filter is more lottery than predictable result. Only in
situation that somebody can use the same type of crystals
producer
and batch results might be comparable.
