Is it possible to implement VCO with a npn transistor

[arnab.bhaumik]

Re: VFO for UHF (144-148mhz) Help please!

is it possible to implement this VCO with a npn transistor???

and please suggest me the stability of the same.......

arnab/vu2bpw

 

[jiripolivka]

Re: VFO for UHF (144-148mhz) Help please!

Dear KE5HOB:

Please study ARRL Handbook and similar amateur radio VHF/UHF books.
You will find that using a VCO at >100 MHz in a receiver makes not much sense due to its instability, by temperature, mechanical, etc.
The correct way is to use a double-conversion superhet concept; the first local oscillator signal is generated by multiplication from a 5-30 MHz quartz oscillator. The IF receiver, say at 10...20 MHz, can then be tuned without problems.
Many hams and designers can use a HF (shortwave) receiver as a tunable IF while before it you add a VHF converter with a stable local oscillator.

My advice is - use a good experience of many hams, well described in ham books and journals.

You can certainly make or buy a VCO at 140 MHz but you will be very disappointed by its instability. Or, otherwise, build a superregenerative receiver for UHF.

 

[karesz]

VFO for UHF (144-148mhz) Help please!

Hey Youngs,
I believe that OM KE5HOB`s VFO problem is after 4 years really finished...
K.

 

[arnab.bhaumik]

Re: VFO for UHF (144-148mhz) Help please!

hii,,,


i am in my workshop now and just build an oscillator ( grounded base), its working but it is drifting around 200Khz per 2 second. totally unstable. still have to see it putting it in a matal box and see how much it can drift.....

anyway, it seems that i cant do it anything rather than just using it as a signal sourcee....

arnab/vu2bpw

 

[karesz]

VFO for UHF (144-148mhz) Help please!

Can you check what is changing?
For me is these relative big variance & I think its a self heating effect, or it will be heated from the environment!?...
You can/must select some temp coefficient adjusted capacitors, but you have to know what is & how much changing.
Formerly by tube tranceivers it was an allday busines some oscillator to build with different & parallel/serial connected & selected Tc + Value capacitors & from begining so to design _ also their are temp compensated.

In your case is possible not a metell case relevant, but a thermal isolation_if the other effects as capacitances to environment & supply changing effects arent relevant...

Try it pls with an extra stabilysed small supply/Zener & good filtering for your VCO, plus separating/buffer amps!...

With relative simple technique it must be possible to build oscillators up to so GHz & at 10^-5,-6.
These means a stability of 10th of KHz & more and not only in couple of seconds...

I had a project so 17 years ago with two synthesyzers in that_ at 510 & 840MHz, so as I remember their are ca: 10^-6, I didnt used selected Tc capacitors but NP0 & the circuit was built with a short RG 174 Coaxial cable (practically λ/4)as resonant elements
K.

 

[karesz]

DR OM,
I found some documentation over my old & said VCO circuit. Maybe is interesting for you for some other experiment...
If I remember right, the PCBs are 41x45mm & built in a 47x51x23mm Alu case, mounted on an internal podest in hight of10mm, also the FR4 card was practically in midle hight.
I remember, that I did built a ca 140-150 MHz version too, but didnt foud yet some documentation...
K.

 

[arnab.bhaumik]

hii,,
yesterday's experiment was really a crude one. i just wanted to see the grounded base oscillator working. its power supply was raw, all capacitors are very bad quality cheap capacitors and same those resistors. i also suspect that ambient temperature and working temperature of the circuit had to do with the frequency drifting. the next thing i will do is to design a proper pcb for it and select quality parts to build yet another 144MHz vfo.

anyways its working and if i can limit the drift within 10khz /second then i can use it in some purpose (local HAM project)


and thanks for the circuit diagram. i also seen a microwave DRO operating around 11GHz directly and deployed in some serious business. it gave me the idea that we CAN make oscillators directly upto VHF/UHF frequencies and make it stable reasonably.

perviously i was stuck for not having a frequency counter upto GHz range. but just few days ago i built a counter using pic16f628 and u664bs prescaler. it can count upto 1.2GHz. now i am in heaven to do experiment VHF/UHF range to my hearts content.


arnab/vu2bpw

 

[karesz]

Yes, the satellite RX-converters (& much commercial & professional) equipment has dielectric resonator oscillators & filters with really good stabilities...
I have had good resultates with my coaxial cable resonators_in my application, what is similar to end with yours_I can suggest only, try pls an experiment whit that_its really easy to build & works stabile!
I found the said ca 140MHz (exactly worked at 160 MHz) versions schema too_pls find it below...
K.

 

[arnab.bhaumik]

thanks, i will try this circuit withen a few day and put my experiment results here.

with me i also have two circuits for VHF and uhf oscillators directly. one is using grounded base transistor and the another is using two JFETs . i am uploading both those two circuits.

so i am getting quite a project for my weekend fun

1) bring high stabelity with grounded base oscillator.
2) building a co-axial resonator oscillator.
3) building a oscillator using 2 JFETs in vhf/UHF range..


thanks for the update...

arnab/vu2bpw

 

[karesz]

Hi,

Nice scripts_tnx. I know the most works from Rohde practically from the past 30 years_some are in good books to have as low Ph.-noise oscillators/PLLs-Synthesyzersor even patents ...
Shortly I meat him on another forum_it was me a novum, but hes circuits the older knowed!
I thik he has the same publication linked too-as your second one, but I meat it eventually on hes homepage...
Btw:
the coaxial cable resonator is practically an equivalent of the ceramic resonator, with the small difference, that you have every time the desired frequency from it, but a cer.-resonator you must order specially(it will be expensive, not practicable for home users), or eventually short it mecahnically... :-(
By the 160/144 MHz version, make pls the cable free from outer teflon isolation and solder the shild in full length!(of course the shorter resonators in the "xhundred MHz VCOs" need to be similarly soldered too) to the GND! Of course; a folding is possible.
By the higher frequency models was my "resonator" on the left corner on the linked PCBs, the "U-shaping"/Bottom side - between L2 &L3...

Good luck with weekends experiments!
K.