GRID DIP OSCILLATOR by Harry Lythall - SM0VPO question

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Re: GRID DIP OSCILLATOR by Harry Lythall - SM0VPO question

Post by zsolt on Mon Jan 15, 2018 3:09 pm

Hi,
I modified drawing again to depict what i understood



Is it right ? the trim pot would be the 22K you told to use 
Thanks  Smile

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Re: GRID DIP OSCILLATOR by Harry Lythall - SM0VPO question

Post by Densil on Sun Jan 14, 2018 10:23 pm

And there is one more thing - harry wound all his gdo coils as one big coil. i used a resistor to feed the power in one end with no center tap and the current drawn is less dependant on the frequency. i put the resistor in the coil so i can have a different value for each coil. selected them on test.
/D

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Re: GRID DIP OSCILLATOR by Harry Lythall - SM0VPO question

Post by Densil on Sun Jan 14, 2018 9:47 pm

Hi zsolt, i built harrys gdo and it works grate. i have a couple of comments that can help you.

if you want to feed the adc input then you only need a resister like 22k from the source without any diode at all. harrys design is a bit too sensitive with the meter in a bridge so i just had a voltmeter on the source of the fet. that works fine. i think harry uses very loose coupling so he has a smaller dip otherwise the external circuit pulls the gdo and he once described using a loop feeding a loop so he could push the second loop inside a can.

the parallel fet in your drawings looks good and i will give that a try myself.

ascii art is a bit naff on this forum because the characters are monospaced but spaces are not. you can use a - instead of a space and change the colour of them to white so they dont show the dashes. the dash - has the same space as a character.

ill let harry answer your other questions cos hes the expert. he said he made this circuit a few times for the last 35 years.
/D

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Re: GRID DIP OSCILLATOR by Harry Lythall - SM0VPO question

Post by zsolt on Wed Jan 10, 2018 7:51 pm

hi,
interesting things you say here maybe i ll give a try later on... what i wanted to do is to eliminate the big dial and the measuring instrument. I taught that both information s can be displayed on the LCD. And it can , at least the frequency gives no trouble . The dip gives trouble  , i tried to display a bar graph on the second row  , something like this : (hope the text is not otherwise formatted here when i post) 
_______________________
| frequency:  8.5 Mhz          |
| level : ||||||||||||||||||     |
|______________________|
When the dip occurs the bar graph should decrease. Actually it does . I discovered that the amplitude of the signal is very frequency dependent .
Oh and i discovered the the dip is not always negative . At some home appliances the amplitude  is increasing very much instead of decreasing .
Anyway it's interesting  how useful and versatile a little sensitive oscillator can be. It saved the day Smile  , from 100 labels 40 where bad . And i could also see that different labels are not behaving the same way . Probably your GDO should not be digitalis-ed at all  Very Happy , but I m shore that a stronger controller having a 40 Mhz clock could make it .

PS: i don't know how to parallel FET transistor in that scheme . Did you suggest to put an other FET in the circuit with Gate and Source in parallel with the existing transistor just that it's Drain should have only the micro-controller input and a load resistor separately  ? hope you don't mind i vandalized your drawing to show what i understood

Oh and an other question , where would you connect the amplitude detector circuit in your scheme ?

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Re: GRID DIP OSCILLATOR by Harry Lythall - SM0VPO question

Post by Admin on Wed Jan 10, 2018 12:36 pm

Ok, I understand.

When I give my classroom demonstrations I usually have a 2-turn loop on the input to the counter. I feed the loop over the GDO loop, then use the GDO in the normal way. This is good for about 4 to 25MHz but the counter loop will have to be adjusted for higher or lower frequencies.

But this method is not suitable if you want to do as you do: have an integrated instrument.

Perhaps you could add a counter pickup-loop built into each coil? Then you can have a diffrerent and optimal loop for each band?

Just a suggestion.

Finally, have you thought about using a paralled FET (source of both FETs connected) to get an isolated output from the GDO? This could be an elegant solution.

BR Harry  - SM0VPO

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Re: GRID DIP OSCILLATOR by Harry Lythall - SM0VPO question

Post by zsolt on Sun Dec 31, 2017 1:25 pm

hi , i managed to count the frequency with a 2 turn coil in the gdo , i was thinking about getting the amplitude into the mcu in order to display on lcd ... i found out that detecting the dip is already done in first place .When the dip occurs  the mcu shows zero frequency on the display (probably the level is to low for the input pin). So now i know when the dipp is present just that i don't know at which frequency  Very Happy  , I could tweak around the program to display the last non zero value for frequency when the dip is present . I don't think i can fully  upgrade your GDO to digital, the 2 events are antagonist for the mcu . It does the job anyway .

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Re: GRID DIP OSCILLATOR by Harry Lythall - SM0VPO question

Post by Admin on Sun Dec 31, 2017 11:18 am

Hi Zsolt,
One possibility for measuring the GDO is to take a series resistor (47K ?) and 1nf capacitor from either the gate or the drain to the input of your counter.

With the GDO there is about 10v P-P at those two points so you should be able to sniff off a little RF without affecting the frequency (much).

Anyway, I want to wish you a very Happy New Year.

Interesting fact, today, everybody who is legally an adult (over 18) were born in the 1900's. All "minors" (under 18) were born in the 2000's.

Vdry best regards from Harry - SM0VPO

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Re: GRID DIP OSCILLATOR by Harry Lythall - SM0VPO question

Post by zsolt on Sat Dec 30, 2017 6:52 pm

hi , 
first of all best wishes for all . About the gdo 1 , since i'm using a self made frequency meter with 2x8 LCD i taught that i could display on the second row also  the amplitude in a form of a bar graph. With this i could eliminate the microampermeter ( i used a magnetoelectric device which is not performing quite so well ) .
I have an analog pin left free, and i can use internal 1.2V reference for ADC if needed.I have no idea if it can work or not, but where would you connect the analog input (with respect to GND) in the GDO1 circuit, in order to do this ?

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Re: GRID DIP OSCILLATOR by Harry Lythall - SM0VPO question

Post by zsolt on Sun Dec 24, 2017 3:46 pm

HI,
it was a great time , and so fun . Actually i'm glad for having no computer back then  .

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Re: GRID DIP OSCILLATOR by Harry Lythall - SM0VPO question

Post by Ivan on Sun Dec 24, 2017 9:51 am

Hi,
3,5 MHz (80 m) band is not free. It is one of the hamradio shortwave bands. There are five distinct frequencies inside that band reserved for foxhunting. The "foxes" are allowed to send certain CW patterns only - perhaps E, I, S, H and 5 (. .. ... .... .....).

BR Ivan

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Re: GRID DIP OSCILLATOR by Harry Lythall - SM0VPO question

Post by zsolt on Sat Dec 23, 2017 6:16 pm

hi , indeed we have a radioclub ... it's complicated .What's with the 3.5 MHz frequency ? isn't that free ? i remember when i was a little kid we  used to play a so called game  fox hunting (don't know how to translate the term .)  Basically our electronics teacher used to hide some transmitter, usually 3, those where the foxes ,  and we had to find them with our receivers (hunters) .I remember that those receivers where 3.5 Mhz .

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Re: GRID DIP OSCILLATOR by Harry Lythall - SM0VPO question

Post by Ivan on Fri Dec 22, 2017 6:52 am

Hi Zsolt,
there is a central hamradio club in almost every country, and a governmentory radiocommunications regulator, too. You should get all the basic information on their webpages: hamradio bandplans, technical conditions (maximum radiated power, stability of frequency, spectrum purity,...), exams to pass etc.  To build or purchase your own transmitter legally, you must have a license and a callsign from the regulator office.

BR from Ivan OK1SIP

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Re: GRID DIP OSCILLATOR by Harry Lythall - SM0VPO question

Post by zsolt on Thu Dec 21, 2017 3:25 pm

Ivan wrote:Hi Zsolt,
a range of a transmitter depends very much on its antenna, ground system, output power, ionosferic conditions and many many other things.
A HF CW transmitter with maximum legal power for hams can send its signal twice around the globe using ionosferic reflections.
A VHF /UHF CW transmitter with maximum legal power for hams can send its signal from Earth to Moon and get reflected it back.

VBR from Ivan
WOW !    bounce
Where can i found this data ? about ham and max legal power ?

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Re: GRID DIP OSCILLATOR by Harry Lythall - SM0VPO question

Post by Ivan on Thu Dec 21, 2017 2:07 pm

Hi Zsolt,
a range of a transmitter depends very much on its antenna, ground system, output power, ionosferic conditions and many many other things.
A HF CW transmitter with maximum legal power for hams can send its signal twice around the globe using ionosferic reflections.
A VHF /UHF CW transmitter with maximum legal power for hams can send its signal from Earth to Moon and get reflected it back.

VBR from Ivan

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Re: GRID DIP OSCILLATOR by Harry Lythall - SM0VPO question

Post by zsolt on Thu Dec 21, 2017 12:44 pm

hi,
no method functioned or all my sample tags are bad . I think that for first i need a 100% functional tag . Then i'll try again .
Ps: how far could i transmit with a cw transmitter ?

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Re: GRID DIP OSCILLATOR by Harry Lythall - SM0VPO question

Post by Ivan on Thu Dec 21, 2017 7:13 am

Hi Zsolt,
maybe you do not need an oscillator at all. If a coil produced a square pulse (switched DC in fact), the metal strips should start vibrating. Their vibration should be picked up by the same or another coil just after the pulse ends.

BR from Ivan

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Re: GRID DIP OSCILLATOR by Harry Lythall - SM0VPO question

Post by zsolt on Wed Dec 20, 2017 6:39 pm

hi ,
the transformer coils let me go down to 56 kHz indeed ,just that i can't dip the 56 kHz RF tag's with that construction. We have the 8.2 MHz tags which can be verified with your first GDO perfectly because these tags are LC circuits . The 56 kHz tags are not LC , according to wikipedia:  they have  a strip of magnetostrictive, ferromagnetic amorphous metal and a strip of a magnetically semi-hard metallic strip, which is used as a biasing magnet (to increase signal strength) and to allow deactivation. These strips are not bound together but free to oscillate mechanically. 
These give me some trouble to check .... for now i only got the idea to build an 56kHz oscillator and use it to attack an audio amp ( i have one with some TDA2... audio chip, that according to datasheet is not attenuating very much in that frequency  range far as i remember ) Instead of speaker i'm willing to put an air wound coil to vibrate up the tag . Near the tag i will put a pick up coil connected to a scope . I believe that after i suddenly stop the amp, if the tag is good it  will still vibrate  a little to induce something in  the pick up coil connected to the scope . All this are presumptions , i have no idea if this works like that , i'll do it anyway Smile
Thanks and best wishes from me also !

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Re: GRID DIP OSCILLATOR by Harry Lythall - SM0VPO question

Post by Admin on Wed Dec 20, 2017 6:41 am

Hi Zsolt,
Great that you find so many projects interesting. At the moment I have several projects on the bench, but one big project needs a lot of time, and I am not able to have that time. Handicapped wife, Christmas, 24/7 callout etc. But they will come.

As regards the lower frequency limit of the GDO, there is no lower electrical limit. My original GDO covered 80kHz and I used a mains transformer coil to try lower limits. I had it down to much less than 1kHz. Unfortunately it was with the iron core, which made it useless as a dip meter, but it worked as an oscillator.

You could try getting two of these transformers. The 230V winding is on a pre-wound former, so you could strip them down and put the two 230V windings in series to get a ready-made VLF coil. Just a suggestion. You may have to use a parallel resistor to damp it a little to get a stable performance.

56kHz?? Here in Sweden they use 8.2MHz for the shop anti-theft alarms. I must confess to having a bit of fun with them, but as Maj-Lis says, men never grow up.




Good luck with the projects.

Very best regards from Harry - SM0VPO

PS - I am now getting e-mail post notifications :-) Don't know what the problem was, just went in the admin pages, switched OFF then switched ON again.

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Re: GRID DIP OSCILLATOR by Harry Lythall - SM0VPO question

Post by zsolt on Tue Dec 19, 2017 4:12 pm

thanks ,
actually i found many interesting pages here and some things i would try out .. regarding the GDO , is it possible to go down to 56 kHz with this type of oscillator ? I'm checking RF anti-theft labels with it . (we buy them and print them )

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Re: GRID DIP OSCILLATOR by Harry Lythall - SM0VPO question

Post by Admin on Tue Dec 19, 2017 2:54 pm

I use a frequency counter based on a 16F628 with a BC547 preamplifier. I always use a 1-2 turn loop since they are two separate units.

By the way, I have activated your account zsolt and you have all the permissions. Welcome to HHH SM0VPO forum. Hope you find a lot to interest you and thank you for participating.

Very best regards from Harry SM0VPO

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GRID DIP OSCILLATOR by Harry Lythall - SM0VPO question

Post by zsolt1 on Mon Dec 18, 2017 6:54 pm

hi, i recently built the GRID DIP OSCILLATOR by Harry Lythall - SM0VPO . It works like charm .  I would like to use a frequency meter attached to it . I have several frequency meters built with PIC16F microcontrollers, some have some kind of input signal conditioning and some not . My trouble is that when i directly connect the frequency meter in whatever point,  it kills the oscillator or it considerably changes it's frequency . The only way i could measure frequency is with one pick up coil of 1 or 2 turns placed near the GDO . 
I would like to use a input pin (ex. timer0 clock input) with TTL level to get the frequency , what circuit should i search for ?
Thanks

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