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Hi Kumar,

in my experience building a VFO, you may need to adjust number of turns on your coils to get the desired tuning range when you turn the trimmer.

As for your BFO, you may need to know your xtal filter center freq, and then tune your BFO for USB or LSB operation, on LSB, BFO should be on the upper edge of your xtal filter bandwidth, on USB, at lower edge of xtal filter. I test my xtal filter (10MHz xtal) with a signal generator and oscilosope, i tune the signal generator from 9.995MHz to 10.005MHz and watch the output on my osciloscope, i marked the freq when it first shows an output to the scope, again marked the higest output and the lowest until its gone, from the result, i get 9.996MHz at the lower edge, and 9.998MHz at upper edge, i operate my BITX at 40m, so i tune the BFO for LSB operation which is 9.998MHz at the BFO.

there are method to measure your ladder filter using VFO, BFO, and AF Stage, pls read back to the mailing list archive.

rgds
julius





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On 6/25/2005 at 8:58 AM kumar gautam wrote:

Hello,
In my bitx20 BFO shows 9.995 MHz. and in VFO section when i add 2j gang
capacitor my VFO shows 4.000 to 4.180 MHz(when trimmer shifted to
4.000MHz) and after tuning Trimmer(shifted to 4.150MHz) it shows 4.180 to
4.410Mhz.
After trying various type of variable capacitors i coul'd not find entire
range i.e. 4.000 to 4.400MHz.
Kindly help me in this regard i.e.
1. what is the exact frequency of BFO.
2. What modification should i do for correcting the VFO.
also could i connect T1,T2 and T3 legs in any direction or it is coneected
in any direction.
with 73's
de kumar gautam
fromgautam@...



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Wise words from Julius.
Several postings are related to this subject.
It can be measured with a tone generator connected to the microphone
connection or with the sound card of the PC.
Dig in de messages, the photos and links directories and you will find
more issues that will help you getting up your rig and to make
understand 'why' and 'how'.
Best regards,
Chris.

there are method to measure your ladder filter using VFO, BFO, and

AF Stage, pls read back to the mailing list archive.

rgds
julius

I've been reading JF1OZL article, which i myself sometimes questioned about BFO setting for USB or LSB operation, Arv K7HKL also provide me the same information about it, and this is what JF1OZL wrote:

----Please remember that "when the mixer generates the difference of two input signals, the USB changes LSB, LSB changes USB", and, " when the mixer generates the sum of the two input signals , USB became from USB, LSB became from LSB".----

rgds
julius


* REPLY SEPARATOR *

On 6/28/2005 at 7:26 PM vdberghak wrote:

Wise words from Julius.
Several postings are related to this subject.
It can be measured with a tone generator connected to the microphone
connection or with the sound card of the PC.
Dig in de messages, the photos and links directories and you will find
more issues that will help you getting up your rig and to make
understand 'why' and 'how'.
Best regards,
Chris.

there are method to measure your ladder filter using VFO, BFO, and

AF Stage, pls read back to the mailing list archive.

rgds
julius

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--- In BITX20@..., kumar gautam <fromgautam@y...> wrote:

Hello,
In my bitx20 BFO shows 9.995 MHz. and in VFO section when i add 2j

gang capacitor my VFO shows 4.000 to 4.180 MHz(when trimmer shifted to
4.000MHz) and after tuning Trimmer(shifted to 4.150MHz) it shows 4.180
to 4.410Mhz.

After trying various type of variable capacitors i coul'd not find

entire range i.e. 4.000 to 4.400MHz.

Kindly help me in this regard i.e.
1. what is the exact frequency of BFO.

Varies depending on the crystal filter characteristics. Ideally
it should be tuned to 300hz down the lower frequency edge (assuming
upper sideband) of the filter slope. To do that precisely you have
to know the filter shape. The alternate way is to listen to good
signals and start with the bfo low and tune it up for natural
sounding recieve signal. Then there may be some fine tuning of the
BFO once you have a QSO for best TX sound.

2. What modification should i do for correcting the VFO.

Try fewer turns on VFO coil. The tuning diode the 22pf capacitor
connected to the tuning diode may need a slight increase in value.

also could i connect T1,T2 and T3 legs in any direction or it is

coneected in any direction.

?? I am not certain what you are asking.

Allison
KB1GMX

Gautam

I am assuming that you are using the same size VFO inductor and capacitors as
specified by Farhan. If you are using the original design with the 36V zener
diode as a VFO fine tuning capacitor, you might try a different diode. They
do not all show the same capacitance value or range. If this does not work,
it is possible to use other diodes in place of the zener. My BITX20 uses a
Red LED as the tuning diode.

It is possible that you have connected the tuning diode using the wrong
polarity. Try reversing it to see what the results might be.

Since the tuning diode contributes only 10 pf, it can be disconnected
temporarily and the VFO tested without it.

If you do not have a way to measure capacitance, the value of your variable
capacitor can be measured using the simple capacitance test circuit shown in
<>. This
might help to verify that your tuning capacitor is really 365 pf. With the
capacitor completely open it should measure less than 20 pf.

Arv K7HKL
_._