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VU3NSH VFO

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VU3NSH VFO

Postby iw3sgg » Tue Jul 12, 2011 2:54 am

Hi at all,I hope that I find good place for this topic.
I need same information about MULTIPURPOSE VFO FOR YOUR RIGS
by N.S.Harisankar, VU3NSH.
How is the power supply Vcc???
How calculate LPF for 2Mhz?,I need a 50ohm output but how is the T3 impedance output?
It is possible to replace the L1 with Amidon toroid???If yes what type for 2Mhz???

Thanks for repply.

iw3sgg Noris.
73
iw3sgg
 
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Postby vu3cns » Wed Jul 13, 2011 8:37 pm

How is the power supply Vcc???

The circuit uses a 9.1V zener diode (D1) to regulate power, so the Vcc may 12 (approx).
How calculate LPF for 2Mhz

It is modification of VFO used in RM96 rigs, so you can use L14 in RM96 circuit as L2, because it is also a 2MHz output.
It is possible to replace the L1 with Amidon toroid?

Yes, replace with an equivalent inductance, search in google to find inductance formula for amidon toroids.
73's
CNS
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Postby iw3sgg » Fri Jul 15, 2011 1:07 am

Hi vu3cns,
thanks for reply but sorry for delay but I was out for work.
Really I want to modify the vfo for 2.0-2.1 MHz.
How I can measure the output impedance of transistor T3 for calculate with AADE program
the correct values for low pass filter????

Thank very much for the main power tension value.

An question for you.

Do you use a special program to compute
values ​​of inductance and capacitance for the resonant circuit of the VFO?

Thank for reply.
Best regards.
73 de iw3sgg Noris
iw3sgg
 
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Postby vu3cns » Fri Jul 15, 2011 10:09 pm

Hi,
I think you can use the small signal model of a CE amplifier to determine the o/p impedance of T3.
Do you use a special program to compute
values ​​of inductance and capacitance for the resonant circuit of the VFO?

No, I never used anything.
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Location: Calicut

Postby iw3sgg » Sun Jul 24, 2011 2:24 am

vu3cns wrote:Hi,
I think you can use the small signal model of a CE amplifier to determine the o/p impedance of T3.
Do you use a special program to compute
values ​​of inductance and capacitance for the resonant circuit of the VFO?

No, I never used anything.


Thanks!
I use HP network analyzer to determine the output Z !!!
Pretty!
Thanks!
iw3sgg
 
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Postby iw3sgg » Fri Aug 12, 2011 1:31 am

For all people that is interesting about this vfo same informations:

I use a 200pF variable capacitor.
With a T50-6 amidon toroid same experiments:

a) 40turns c=0 1,70544Mhz
c=200 1,59924Mhz

b) 34turns c=0 1,96491Mhz
c=200 1,84225Mhz

c) 31turns c=0 2,15704Mhz
c=200 2,02232Mhz

But the output signal is not very stable in amplitude,I need to check the voltage across CE of the firs transistor.
Coming soon about the build up of the vfo.

Bye at all!



Bye!
iw3sgg
 
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Output signal not stable.

Postby iw3sgg » Sun Aug 14, 2011 2:09 am

Same trouble:

Vbe of T1 now is -0,346 Volt

I think that is a lot of feedback.
I try to increase the Vbe by increase the capacitor C4.
C4 of 1000pF plus a parallel capacitor of 3,3nF increase the Vbe at +0,26 Volt but
the output signal is not stable.
Why????
C4 and C5 is a frequency attenuator ????
I need to modify the C5 ???
Someone can help me????
Bye.
iw3sgg
iw3sgg
 
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Postby mvs sarma » Mon Aug 15, 2011 11:19 am

iw3sgg wrote:For all people that is interesting about this vfo same informations:

I use a 200pF variable capacitor.
With a T50-6 amidon toroid same e...........

But the output signal is not very stable in amplitude,I need to check the voltage across CE of the firs transistor. Coming soon about the build up of the vfo.Bye at all! Bye!


Can you consider the listed suggestions and experiment a little more

Image[/img]
Regards
Sarma
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Postby iw3sgg » Wed Aug 17, 2011 1:35 am

Can you consider the listed suggestions and experiment a little more

YES Sarma,why not???

I found the problem, the second transistor was damaged and I replaced it.
Now the signal is stable but in my opinion too low.
I think I have a problem with outbound filtering, which was originally
designed to eliminate everything above 2MHz.

I used the compound 6-series Amidon T-50 because is suggested in the book EMRD W7ZOI for thermal stability.

If I have same time I do same experiments again.

Best regards.
iw3sgg
 
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Multipurpose VFO for your rigs

Postby IK6AIZ » Sat Nov 19, 2011 3:59 am

hi to you,
I have made the multipurpose VFO,it's very good but I need to ask something and know something about it.
First,I want to ask how to calculate the low pass filter for other frequencies.In this moment I need the data for 2.8 to 3 Mhz.
The second matter is that I measured a negative voltage between emitter and base.I used the values in the schematic diagram but while the transistor doesn't work thw value is 0,35 volts but while working the voltage is quite negative.What could I do to solve this problem?
Many and many thanks and wait for your answer.Good work and
73 de Ciro IK6AIZ. :D :D
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Postby mvs sarma » Sun Nov 20, 2011 7:44 pm

IMHO, while the oscillator is working , it is natural to have such observations like negative voltage.

for a clearer appreciation, try to implement a small oscillator, of say 1MHz with LC, there also you wont be able to measure, though you might have provided the bias, emitter resistance , etc

the base emitter junction rectifies the frequency generated and passes one half of the signal through it. thus , i feel you measure negative voltage.
Regards
Sarma
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Homebrew multipurpose VFO

Postby IK6AIZ » Mon Nov 21, 2011 10:16 pm

Thanks a lot really,dear Sarma.
I read in the article"(...)VU2ARA never disclosed the exact principle about a positive voltage at emitter-base while oscillating(...)", and so I wanted to ask you about this.So,thanks very much because you cleared a very important thing to me.
Surely I'll follow your advice and I'll do the measures.If you like,I'll tell you about my observations.
I agree with your advices and observationa.
See you good job
IK6AIZ
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Postby mvs sarma » Tue Nov 22, 2011 11:01 am

Surely. I am interested to share your observations, as only such sharing help learning and changing wrong concepts that dog us
please do update and I am rather hungry to learn even at my 67th.
Regards
Sarma
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VU3NSH VFO

Postby IK6AIZ » Tue May 22, 2012 4:22 am

Hi VU3NSH,
I realized for the second time your vfo, it's very stable also at 9.3 mhz! But now I need to calculate the output filter for this frequency. I read that in the RM96 the output filter is made with 50 turns on 5 mm slug type coil with ferrite inside. The very gentle Sarma gave me some good advices and told me to use AADE filter program to calculate the data of this filter but I found it difficult because I don't know the real impedance of transistor T3.
Could you tell me what's the output impedance of T3 and how to modify the values of the inductor, and of course also the values of the capacitors of this filter? Sarma also told me that this filter is to eliminate the third harmonic, so I thought that if I use that filter as it is I'll risk to block the fundamental frequency of 9.3 Mhz that I need.
Hoping not to give so much disturb to you, I give my best regards.
Good things.
IK6AIZ Ciro.
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Re: VU3NSH VFO

Postby mvs sarma » Wed May 23, 2012 9:59 am

Today , i have dug up additional information on the coil you are searching for. VU3NSH has published a revised sch for RM 96 Transceiver design where he used the VFO , we are talking about. you can download the zip file.

http://www.hamradio.in/downloads/index. ... 9407ea4296

Here you can observe that the inductor under concern is shown as L14 and is 10mm IFT former wound with 50 T of 36 SWG, as per coils and inductors page there in.
hope this helps. All the best.
Regards
Sarma
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