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increase frequency coverage

 

Hi,

? ? ?Kindly help, Is there a way to increase frequency coverage ?of BITX40 v3

? ? ?from 7.100 to 7.500 mhz ( a 400khz bandwidth or more )? By the way ?my?

? ? ?BITX40 V3 ?is non Raduino ? and ?using the ?stock ?vfo.


? ? Regards,

? ? Ricardo Rivera

??
 

Did you received a schematic with your kit? Can you post it? Is it the same schematic as the version with Raduino only using the coil?

I will need the information to calculate new values for capacitors required for your desired frequency coverage.
--
Ion

VA3NOI
 

No schema included in my kit but it is the same as posted with ?hfsigs web minus the raduino.


On Fri, 3 Feb, 2017 at 8:34, Ion Petroianu
<ion.petroianu@...> wrote:

Did you received a schematic with your kit? Can you post it? Is it the same schematic as the version with Raduino only using the coil?

I will need the information to calculate new values for capacitors required for your desired frequency coverage.
--
Ion

VA3NOI
 

Change the varactor to one that has higher capacitance tune ratio or

Alternatively, add an MV209 or 2109 in parallel with the one on the PCB
The tuning range will increase.

You may need to tweak the trimmer and maybe change some turns on
the yellow VFO toroid.

I was able to do that easily!

73 Raj

At 03-02-2017, you wrote:

Hi,

Kindly help, Is there a way to increase frequency coverage of BITX40 v3

from 7.100 to 7.500 mhz ( a 400khz bandwidth or more )? By the way my

BITX40 V3 is non Raduino and using the stock vfo.


Regards,

Ricardo Rivera
 

hi do you mean ?to reduce turn number in L4 by how much turn? what is the inductance value for the L4 nominal?


On Fri, 3 Feb, 2017 at 12:27, Raj vu2zap
<vu2zap@...> wrote:
Change the varactor to one that has higher capacitance tune ratio or

Alternatively, add an MV209 or 2109 in parallel with the one on the PCB
The tuning range will increase.

You may need to tweak the trimmer and maybe change some turns on
the yellow VFO toroid.

I was able to do that easily!

73 Raj

At 03-02-2017, you wrote:

>Hi,
>
>? ? Kindly help, Is there a way to increase frequency coverage? of BITX40 v3
>
>? ? from 7.100 to 7.500 mhz ( a 400khz bandwidth or more )? By the way? my
>
>? ? BITX40 V3? is non Raduino? and? using the? stock? vfo.
>
>
>? ? Regards,
>
>? ? Ricardo Rivera
 

I think it was mentioned before that it is ~6-10 uH.

If one is to increase the frequency span, it cannot be done by changing the inductance alone, unless one increases it by adding more turns.
This is not recommended for a VFO. Generally one should increase the capacitance of the tank circuit.

The suggestion to add another varactor in parallel to the one on the board is a good one. Note though, that the minimum capacitance will have to be changed
to increase the upper end of the frequency range -- hence the thought that one MIGHT have to change the inductance by a bit.

Think of it this way: for a resonant circuit F = 25330/LC where f is in megaherz, L is in microhenries, and C is in picofarads. Find this value for the minimum
and maximum frequencies you want, and try to compare them with what you have. You will probably find that it will take only a few pF to achieve your goal.
I easily changed my range by changing the variable capacitor C93 from 22 pF to 33 pF.

If your C93 is set to minimum capacitance, and the high end of the frequency range is still not enough, then remove a turn or two from the inductor, L4.
If your capacitor C93 is set somewhere above the minimum, then decrease it to raise frequency high end, and increase it to lower it.

But to increase the range, the total capacitance has to be increased, most easily by adding another varactor.

As always, experiment and measure to find the right combination. It works.

john
AD5YE
 

Ricardo,

I can't specifically tell you. You will have to first add the varacters and then see what range you are getting and
then you can message me for further ideas.

First add parallel varacters and see what range you get.

Changing C96 from 100pf to sat 330 or 470 will improve the range as it is. Use NP0/C0G for all
caps in the VFO. My board is very stable drifts only 10-20Hz and 50Hz in the long term.

At the moment I have 3 in parallel with 6uH and 150pf extra and get 200Khz but stabler VFO.

73 Raj

At 03-02-2017, you wrote:

hi do you mean? to reduce turn number in L4 by how much turn? what is the inductance value for the L4 nominal?



On Fri, 3 Feb, 2017 at 12:27, Raj vu2zap
<vu2zap@...> wrote:
Change the varactor to one that has higher capacitance tune ratio or

Alternatively, add an MV209 or 2109 in parallel with the one on the PCB
The tuning range will increase.

You may need to tweak the trimmer and maybe change some turns on
the yellow VFO toroid.

I was able to do that easily!

73 Raj

At 03-02-2017, you wrote:

>Hi,
>
>??? Kindly help, Is there a way to increase frequency coverage? of BITX40 v3
>
>??? from 7.100 to 7.500 mhz ( a 400khz bandwidth or more )? By the way? my
>
>??? BITX40 V3? is non Raduino? and? using the? stock? vfo.
>
>
>??? Regards,
>
>??? Ricardo Rivera
 

Hi John,

I see here that you are suggesting what is right for a normal designs but this one is opposite
12Mhz - VFO, so you need to make the VFO go lower for the range to go higher.

Confused the hell out of me in the beginning. Then I programmed my Racal Dana to do math
and subtract VFO - 11.9985 -> giving me a -7.xxxxx display. The reverse is not available
in the 1992 model. Now with the negative frequency I might have a QSO with aliens eh?

Cheers
Raj, vu2zap

If your C93 is set to minimum capacitance, and the high end of the frequency range is still not enough, then remove a turn or two from the inductor, L4.
If your capacitor C93 is set somewhere above the minimum, then decrease it to raise frequency high end, and increase it to lower it.
 

Oops! You're right, Raj.

The same principles apply...but in reverse.
He still has to experiment, as you suggest, and find out what happens.

john
AD5YE
 

Ricardo,

To calculate the frequency of a Clapp oscillator you should use the information found here:

Now, BitX is using a VFO that oscillates between, roughly 4.5 MHz to 5 MHz.

The C0 in the formula above is the combination of C96 in series with MV209 and those two in parallel with C93, C94 and C95.

The equivalent capacitance of a series of capacitors is calculated as follow:

C eq series = (C1 x C2)/(C1+C2)

The equivalent capacitance of a parallel group of capacitors is calculated as follow:

Ceq parallel = C1+C2+C3+C4

For our circuit C1=C93, C2=C94, C3=C95 and C4=(C96x MV209)/(C96+MV209)

The nominal value of the inductance is stated on the schematic: L4=9 uH, but with the capacitors as per schematic I am expecting more like a 6 uH inductance. I used that value for may calculations.

In my calculation, for the minimum VFO frequency, using the nominal values in the schematic, I ended up with a frequency range of 4.7MHz to 5 MHz, which looks consistent with a band coverage of 7 MHz to 7.3 MHz.

With all those in mind, I think the best option for you is to place a second varactor diode in parallel, add another NPO capacitor of 220 pF or 300 pF in parallel with C96 and verify the new frequency range of your VFO.

It calculates as 4.35 MHz to 4.85 MHz, or a band coverage of 7.65 MHz to 7.15 MHz for 220 pF.

Good luck,

--?

Ion

VA3NOI
 

? ? Finally ?I was ?able to extend the freq bandwidth ?from 6950 mhz till 7520 ?by adding ?1N4007 diode across?
? the original varactor D9 ( very difficult to source varactor ?in my place) and add 200pf on C96 ?and lastly reduce L4 by?
? two turns ?and retuned C93. Thank you all for the good advised given. But noticed also that the output at higher freq
? ?were reduced appreciably any advise ?on how to make the ouput more broadband? ?

? ? Regards ?and 73
? ? Ricardo Rivera
? ? DV3RWR


On Friday, February 3, 2017 7:00 PM, Ion Petroianu <ion.petroianu@...> wrote:


Ricardo,
To calculate the frequency of a Clapp oscillator you should use the information found here:
Now, BitX is using a VFO that oscillates between, roughly 4.5 MHz to 5 MHz.
The C0 in the formula above is the combination of C96 in series with MV209 and those two in parallel with C93, C94 and C95.
The equivalent capacitance of a series of capacitors is calculated as follow:
C eq series = (C1 x C2)/(C1+C2)
The equivalent capacitance of a parallel group of capacitors is calculated as follow:
Ceq parallel = C1+C2+C3+C4
For our circuit C1=C93, C2=C94, C3=C95 and C4=(C96x MV209)/(C96+MV209)
The nominal value of the inductance is stated on the schematic: L4=9 uH, but with the capacitors as per schematic I am expecting more like a 6 uH inductance. I used that value for may calculations.
In my calculation, for the minimum VFO frequency, using the nominal values in the schematic, I ended up with a frequency range of 4.7MHz to 5 MHz, which looks consistent with a band coverage of 7 MHz to 7.3 MHz.
With all those in mind, I think the best option for you is to place a second varactor diode in parallel, add another NPO capacitor of 220 pF or 300 pF in parallel with C96 and verify the new frequency range of your VFO.
It calculates as 4.35 MHz to 4.85 MHz, or a band coverage of 7.65 MHz to 7.15 MHz for 220 pF.
Good luck,
--?
Ion
VA3NOI
M Garza
 

Ricardo,
You will have to change the frequency of the low pass filter.? Please look at L6 - L7 & C160 - C163.? It is currently designed to cut off frequencies higher than 7.35mhz or so.

Marco - KG5PRT?


On Mar 1, 2017 2:40 AM, "Ricardo Rivera via Groups.Io" <rivera761=[email protected]> wrote:
? ? Finally ?I was ?able to extend the freq bandwidth ?from 6950 mhz till 7520 ?by adding ?1N4007 diode across?
? the original varactor D9 ( very difficult to source varactor ?in my place) and add 200pf on C96 ?and lastly reduce L4 by?
? two turns ?and retuned C93. Thank you all for the good advised given. But noticed also that the output at higher freq
? ?were reduced appreciably any advise ?on how to make the ouput more broadband? ?

? ? Regards ?and 73
? ? Ricardo Rivera
? ? DV3RWR


On Friday, February 3, 2017 7:00 PM, Ion Petroianu <ion.petroianu@...> wrote:


Ricardo,
To calculate the frequency of a Clapp oscillator you should use the information found here:
Now, BitX is using a VFO that oscillates between, roughly 4.5 MHz to 5 MHz.
The C0 in the formula above is the combination of C96 in series with MV209 and those two in parallel with C93, C94 and C95.
The equivalent capacitance of a series of capacitors is calculated as follow:
C eq series = (C1 x C2)/(C1+C2)
The equivalent capacitance of a parallel group of capacitors is calculated as follow:
Ceq parallel = C1+C2+C3+C4
For our circuit C1=C93, C2=C94, C3=C95 and C4=(C96x MV209)/(C96+MV209)
The nominal value of the inductance is stated on the schematic: L4=9 uH, but with the capacitors as per schematic I am expecting more like a 6 uH inductance. I used that value for may calculations.
In my calculation, for the minimum VFO frequency, using the nominal values in the schematic, I ended up with a frequency range of 4.7MHz to 5 MHz, which looks consistent with a band coverage of 7 MHz to 7.3 MHz.
With all those in mind, I think the best option for you is to place a second varactor diode in parallel, add another NPO capacitor of 220 pF or 300 pF in parallel with C96 and verify the new frequency range of your VFO.
It calculates as 4.35 MHz to 4.85 MHz, or a band coverage of 7.65 MHz to 7.15 MHz for 220 pF.
Good luck,
--?
Ion
VA3NOI

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