VCO

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radium98
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VCO

Post by radium98 » Thu Dec 21, 2017 7:28 pm

i need some help what is wrong in this vco why it does not oscillate it the scheme correct ?
i tried on a clad copper with bf494 and with bfr91 same
20171217_151744.jpg
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radium98
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Re: VCO

Post by radium98 » Thu Dec 21, 2017 8:09 pm

same on clad copper board no oscillation whats wrong ?
20171219_165831_compressed.jpg
20171219_165755_compressed.jpg
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Albert H
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Re: VCO

Post by Albert H » Fri Dec 22, 2017 1:50 am

Try making the two 22p capacitors 56p and see what happens
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radium98
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Re: VCO

Post by radium98 » Mon Dec 25, 2017 5:09 pm

NOT working what do u suggest as coil 6turns on 6mm diam with 1mm cu will cover the need
is the schematic above okey
i tried with two transistors type bf494 and bfr91
what else ?

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Re: VCO

Post by sinus trouble » Mon Dec 25, 2017 6:34 pm

Seasons greetings Mr Radium! :)
How do you know if its oscillating or not? Have you a oscilloscope to check? I suspect it IS actually oscillating, but not at the frequency you are expecting!
Oscillator frequency will be vastly affected by PCB size, stray capacitance/inductance amongst many other factors!
In the past experimenting with VCOs I would use temporary trimmer caps instead of fixed ones!
Also the coil can be stretched or compressed too!
Remember aswel the varicaps form part of the tank circuit and will be biased slightly via a small DC voltage (usually from PLL or potential divider)
Good luck!
I am as stupid as I look! :|

radium98
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Re: VCO

Post by radium98 » Wed Dec 27, 2017 9:59 am

TXFM 2010-2011 rev c.jpg
Dear sinus trouble thanks for you and happy nye 2018 in advance .sinus the same oscillator dont work on the main transmitter while i change the transistor from bfr90 to 91 to 93 and last with bf494 i used a trimmer pot to bias and scan all the band i also stretched the coil and used many varicaps too same problem i always use a frequency meter ,if u can help me can u manage the vco part on ure bench i will put the necessary files of the transmitter first now is the schematic only ?
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radium98
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Re: VCO

Post by radium98 » Wed Dec 27, 2017 10:03 am

some pictures of my transmitters
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Re: VCO

Post by Albert H » Thu Dec 28, 2017 12:48 am

radium98 wrote:
Wed Dec 27, 2017 9:59 am
TXFM 2010-2011 rev c.jpgDear sinus trouble thanks for you and happy nye 2018 in advance .sinus the same oscillator dont work on the main transmitter while i change the transistor from bfr90 to 91 to 93 and last with bf494 i used a trimmer pot to bias and scan all the band i also stretched the coil and used many varicaps too same problem i always use a frequency meter ,if u can help me can u manage the vco part on ure bench i will put the necessary files of the transmitter first now is the schematic only ?
It looks to me that the coil in the VCO should be where the 100k resistor is, and the varicap that's connected to L1 in the diagram should be grounded! The tuned circuit as drawn might resonate a bit, but it's going to be weak and low Q. For lowest phase noise, the usual wisdom is that the tuned circuit Q should be high.
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Re: VCO

Post by RF-Head » Thu Dec 28, 2017 7:45 am

On the PCB it looks like the coil is in place of the 100K resistor :)

radium98
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Re: VCO

Post by radium98 » Thu Dec 28, 2017 8:30 pm

OH i will try this .thanks

radium98
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Re: VCO

Post by radium98 » Sat Dec 30, 2017 7:15 am

what is the difference between a ferrite bead and a ferrite core batonnet that have turns on it isnt the same ?
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Re: VCO

Post by thewisepranker » Sat Dec 30, 2017 2:03 pm

Toroidal cores (the ring shaped ones) have much higher inductance and Q, and lower leakage inductance than the straight type.
The straight ferrite cores (the top two in your first image) have higher leakage inductance, lower Q and lower inductance than toroidal wound inductors but all of those parameters are better than air inductors. However, the downside is that they saturate at very low current and are quite lossy so aren't much use for output stages.
The bottom ones are ferrite beads. These add only tiny amounts of inductance to straight wires but often it's enough. They're not really inductors in the sense that the wires aren't meant to be inductors in the first place, although they exhibit inductance.

radium98
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Re: VCO

Post by radium98 » Sun Dec 31, 2017 1:57 pm

thank you for the clarifications.happy nye 2018
another question in the schematic i posted above there is a transistor bc238 replaced in my place with bc548 that go out from the tsa5511 ic to the vco varicap i need to know is that normale that i dont have any voltage on its collector and if yes when i should have 12v

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Re: VCO

Post by Analyser » Sun Dec 31, 2017 3:56 pm

radium98 wrote:
Sun Dec 31, 2017 1:57 pm
thank you for the clarifications.happy nye 2018
another question in the schematic i posted above there is a transistor bc238 replaced in my place with bc548 that go out from the tsa5511 ic to the vco varicap i need to know is that normale that i dont have any voltage on its collector and if yes when i should have 12v
BC548 would be fine in place of BC238.

If the voltage at the collector is zero, there may be a fault- check Vcc and 22k resistor.

If the voltage at the collector is low (few volts or less) then the TSA5511 may be detecting a high frequency and trying to pull the VCO to a lower frequency.

The voltage at the collector would be just under 12V if the PLL is detecting a low frequency and trying to pull the VCO to a higher frequency.

Sometimes if the VCO is not working, the PLL doesn't know what to do and the collector can go low or high. You need to make sure the VCO is working first.

radium98
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Re: VCO

Post by radium98 » Mon Jan 01, 2018 10:01 am

Sometimes if the VCO is not working, the PLL doesn't know what to do and the collector can go low or high. You need to make sure the VCO is working first.


that is my case .

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Re: VCO

Post by radium98 » Mon Jan 01, 2018 6:28 pm

isnt this capacitor of 1000pf error in serie and block the dc voltage from the varicap that correct the vco ?
20180101_190159.jpg
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radium98
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Re: VCO

Post by radium98 » Sat Jan 06, 2018 7:49 pm

hello
i dont think that i am too idiot while i have combined smart kit 3watt vco sk1187 with the two controls of this iw1cgw transmitter passing trought the board of control vincent and the second cotntrol rdvv through the tsa5511 input from the external vco and back from the tsa on board through to varicaps and have full band lock
i confirm VCO not and not working it is a mess no one could resolve it .
btw i have changing the varicaps to vhf ones.
please enjoy my contribution from two transmitters :) lol
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Re: VCO

Post by Analyser » Sun Jan 07, 2018 11:54 am

radium98 wrote:
Mon Jan 01, 2018 6:28 pm
isnt this capacitor of 1000pf error in serie and block the dc voltage from the varicap that correct the vco ?20180101_190159.jpg
No, the DC voltage comes to the varicap from the PLL line. You need that capacitor to separate the varicap voltage from the oscillator transistor bias voltage.

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Re: VCO

Post by Analyser » Sun Jan 07, 2018 12:01 pm

Try removing the ferrite bead in the emitter of the BFR90/ vco transistor. Also change the main oscillator coil to 3t, the 6t one you have there on the copper board looks good for about 50MHz.

radium98
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Re: VCO

Post by radium98 » Mon Jan 08, 2018 9:52 am

Analyser thanks for reply ,please look and compare this vco for atv band i tried it before for a project in that time and seems very similar to this fm one so how this work and the fm one not ,can u tel me in caompare to it what should i did .
about coils i have wound 9 turns on 6mm before also not oscillating how many turns you advise to wound .(3turns on 6mm)?
look at the picture i found onces did the same as he said not working but i can see that he removed the 2 27kohms resistor that bias the oscillator transistor and it looks led liting .
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