70kHZ transmitter

[WM6]

If one need a 70kHz transmitter with exact frequency, I suggest this solution:

1.
Use this module from eBay ($38 + free shipping):

0.01- 5MHz DDS Function Signal Generator Module

http://www.ebay.com/itm/0-01-5MHz-DDS-Function-Signal-Generator-Module-Wave-New-/270864768941

2.

Signal generator has enough amplitude to act as transmitter you need, but if you insist that you need more power, then connect signal generator to this module from eBay:

Mono 25W Audio Amplifier Module Board, Based on LM1875

http://www.ebay.com/itm/Mono-25W-Audio-Amplifier-Module-Board-Based-on-LM1875-/400244737945?pt=US_Home_Audio_Amplifiers_Preamps&hash=item5d30720799

Do not drive it with full power - 1/10 of max power, no more.

Inductance of antenna (ferrite core or air core - the last one is better) have to be about 50mH. Exact value depend of antenna windings stray capacitance. You need to connect antenna instead of loudspeaker.

Of course this transmitter can generate any other arbitrary frequency too (for some very different antenna inductance need to be recalculated).

Use sine wave.

[mustefa ubram]

tank you very much freind
I have a problem in calculating the period number and size of the ferrite coil.Get tips on how to calculate the winding.If there is a formula to give.
If I have a signal generator, and can help to strengthen the ferrite Can I send a wave?
How?
tanks
ubram

[WM6]

tank you very much freind
I have a problem in calculating the period number and size of the ferrite coil.Get tips on how to calculate the winding.If there is a formula to give.
If I have a signal generator, and can help to strengthen the ferrite Can I send a wave?
How?
tanks
ubram

It is simple, if you have L-meter (inductance meter).

You need to wind 10 (or better 20 or 30) testing turns of wire (diameter about 0.3 or so) on ferrite rod antenna you have.

Then measure inductance.

Par example:

If you wound 30 testing turns and then measured inductance is 15mH, then you calculate total turns this way:

30 / 15 = 2

This mean that you need 2 of turns to get 1mH.

To get 50mH you need 50x2(turns)=100 (turns).

So you need 100 turns in total on your ferrite rod to get 50mH ferrite cored antenna.


Ferrite cored transmitter antenna is not the best solution for TX, air cored antenna is better. Of course it depend of what you need and what you try to build. If you need "shielded" (i.e. mounted in a tin can) antenna (to radiate in one direction) ferrite core antenna can be better solution than air core.

[mustefa ubram]

It is simple, if you have L-meter (inductance meter).

You need to wind 10 (or better 20 or 30) testing turns of wire (diameter about 0.3 or so) on ferrite rod antenna you have.

Then measure inductance.

Par example:

If you wound 30 testing turns and then measured inductance is 15mH, then you calculate total turns this way:

30 / 15 = 2

This mean that you need 2 of turns to get 1mH.

To get 50mH you need 50x2(turns)=100 (turns).

So you need 100 turns in total on your ferrite rod to get 50mH ferrite cored antenna.


Ferrite cored transmitter antenna is not the best solution for TX, air cored antenna is better. Of course it depend of what you need and what you try to build. If you need "shielded" (i.e. mounted in a tin can) antenna (to radiate in one direction) ferrite core antenna can be better solution than air core.

tank you very much dear freind

[WM6]

Here proposed TX configuration can be used till to 150kHz, even more. Of course not with same antenna specifications given here.

For frequencies 70kHz +-10kHz antenna even do not need to be recalculated.

[mustefa ubram]

.
Ferrite cored transmitter antenna is not the best solution for TX, air cored antenna is better. Of course it depend of what you need and what you try to build. If you need "shielded" (i.e. mounted in a tin can) antenna (to radiate in one direction) ferrite core antenna can be better solution than air core.

dear wm6
Is the ferrite core and reflector antennas can be directly sent 70kh frequency?
Frequency of 70 kHz with a transmitter power is enhanced to within 50 meters sent?
Changes in the frequency or electromagnetic radius of 50 meters on the ground with metal?in coil ANTENNA and ferrite core?

[WM6]

dear wm6
Is the ferrite core and reflector antennas can be directly sent 70kh frequency?
Frequency of 70 kHz with a transmitter power is enhanced to within 50 meters sent?
Changes in the frequency or electromagnetic radius of 50 meters on the ground with metal?in coil ANTENNA and ferrite core?

Sorry mustefa, my English is very bad. I do not understand your questions.

[WM6]

Hello Barbarossa, this can be your solution. First use signal generator to check your GG receiver exact frequency, then use the same to build TX stage working at the same frequency. Use round or square antenna so you can play with TX wave propagation (polarization) combined with proper TX distance.

[Mike(Mont)]

Just a quick note. Those frequency generators are rejects. They did not pass the quality standards. You pays your money and you takes your chances.

[WM6]

Just a quick note. Those frequency generators are rejects. They did not pass the quality standards. You pays your money and you takes your chances.

Reject by NASA or MikeMontLab?

If you can find something better and more precise (look at data below) for $38, then please tell us:

Frequency range:0.01Hz ~5MHz(SG1005)
Resolution:0.01Hz
Frequency Stability:±1×10-6
Frequency accuracy:±5×10-6
Sine wave distortion:≤0.8% (reference frequency is 1kHz)

[Mike(Mont)]

I speak from first hand experience, so yes I guess it is from Mike(Mont)'s lab.

[Mike(Mont)]

Sorry, posted this on the wrong thread.

I'm not saying the chip is bad. It's the hardware/controls that is the weak link.

[Geo]

Hi WM6.
I need something like your schematic for an experiment to locate caves. I must use a wire 150 ... 200m as antenna and at the end it will be grounded. Have you any program to calculate the antenna resistance so to match it with the amplifier??

Regards

[WM6]

Hi WM6.
I need something like your schematic for an experiment to locate caves. I must use a wire 150 ... 200m as antenna and at the end it will be grounded. Have you any program to calculate the antenna resistance so to match it with the amplifier??

Regards

Hi Geo,

You mean end of air cored coil antenna cold wire end connected to circuit ground (similar as on block schema in my first post but without ferrite core) or straight antenna wire end grounded in soil?

In second case (straight antenna wire end grounded in soil) there is no way to proper adapt resistance of 150m wire at VLF band to your amplifier output. But if you insist on this configuration, forget resistance and drive your amplifier at max 25% of its power. Another solution is to use (for <30khz band) an old speaker transformer (for 4-8 ohm speakers) connected in reverse to amplifier (Warning: high voltage at output!) and max. 50% of amp. power. For higher frequencies use ferrite transformer (if you build one on bigger ferrite toroid primary have to be 4 ohms and secondary windings at your wish - say 50Vpp to not be dangerous).

In first case (air cored coil antenna cold wire end connected to circuit ground) you chose antenna resistance according technical specification of amplifier you use, which is in amplifier from post above about 4 Ohms or a little more. You do not need special antenna tunning (SWR) as on HAM bands. Never drive your amplifier at more than 75% of max power.

[Geo]

Hi Geo,

You mean end of air cored coil antenna cold wire end connected to circuit ground (similar as on block schema in my first post but without ferrite core) or straight antenna wire end grounded in soil?

In second case (straight antenna wire end grounded in soil) there is no way to proper adapt resistance of 150m wire at VLF band to your amplifier output. But if you insist on this configuration, forget resistance and drive your amplifier at max 25% of its power. Another solution is to use (for <30khz band) an old speaker transformer (for 4-8 ohm speakers) connected in reverse to amplifier (Warning: high voltage at output!) and max. 50% of amp. power. For higher frequencies use ferrite transformer (if you build one on bigger ferrite toroid primary have to be 4 ohms and secondary windings at your wish - say 50Vpp to not be dangerous).

In first case (air cored coil antenna cold wire end connected to circuit ground) you chose antenna resistance according technical specification of amplifier you use, which is in amplifier from post above about 4 Ohms or a little more. You do not need special antenna tunning (SWR) as on HAM bands. Never drive your amplifier at more than 75% of max power.

Hi WM6. I am interesting for the second case. Frequency will be 100Khz so not so good for audio transformer. Ferrite core maybe is a solution!!!!. I want to have a strong signal at distance of 10...30m far from antenna so i believe that there is not need for high power.
2...3 watts maybe is enough

Regards