Need Help in Loop Antenna Building

[RadioRon]

Do you mean Pierce Oscillator for the oscillator built using HEX Buffer IC and crystal? I have built the circuit of it, but the output suffers from severe distortion... I have built the oscillator using crystal as well... But it is not working...

Again, for the filters, is the enclosed filter is the one in your mind?

Yes, the second link, Pierce Oscillator using 74HC04 buffer IC is very close to what I was suggesting. It is necessary to put additional buffer amplifiers between the oscillator and the low pass filter to provide enough drive for the low impedance looking into the filter. Connect the remaining five gates in parallel to be this driver. I have built similar to this before and the distortion is low. In any case, distortion is not a problem because your output filter should eliminate all harmonics, which will clean up the waveform to be a sine wave. Your output filter must have at least 20 dB attenuation at 2xfc.

If there is not enough power from this kind of circuit, it is easy to add one additional discrete amplifier using an NPN transistor.

As for the output filter, your design is ok, but I was thinking of a simpler configuration where L2 and L4 are omitted and C2 and C4 are small value, high impedance. In my simplified configuration, it is necessary to tap into the first resonator made up of L1 and C1 by either tapping into the coil, or using two capacitors to couple in. In this way, the low source impedance does not load the Q of this tank circuit. C2 would be a small value, sufficient to couple energy to L3, C3 which would be resonant. C4 same as C2. The output would also have to tap into the L5,C5 resonator by tapping the coil or by splitting C5 into two values and connecting between them. This type of configuration is simple and easy to tune. You then have three tank circuits that all have high impedance at their tops, and high Q for good selectivity. The loss through such a circuit is reasonably about 2 dB or less.

 

[Harros]

Whats the difference between crystal and crystal oscillator? I can hardly purchase a 1MHz crystal at my place, but the 1MHz crystal oscillator is easy to get here...

 

[RadioRon]

Whats the difference between crystal and crystal oscillator? I can hardly purchase a 1MHz crystal at my place, but the 1MHz crystal oscillator is easy to get here...

A crystal is a small passive component with two leads. Inside the component is a small piece of quartz rock connected to the two wires. It is a piezoelectric device used as one of many components to make up an oscillator.

A crystal oscillator is an active circuit containing several components configured to oscillate when DC power is applied. A crystal is one of the internal components and is used to determine the frequency of the oscillator.

Your previous posting had a circuit containing a 2N2222 and a crystal amongst other things. That is an oscillator. The single component shown as a kind of capacitor with a rectangle between the plates, that is a crystal.

 

[Harros]

I cant simulate the circuit by connecting the gates in parallel... Why this happens? Any suggestion that I can do to make the simulation runs? I am using MultiSim to perform the simulation.

 

[RadioRon]

I cant simulate the circuit by connecting the gates in parallel... Why this happens? Any suggestion that I can do to make the simulation runs? I am using MultiSim to perform the simulation.

I don't know. Hopefully someone else can answer this question.

 

[RadioRon]

The way to estimate your range is as follows:

calculate path loss (PL) = RxSens (dBm)-Ptx(dBm)-Gtx-Grx

Since we are in near field, we cannot use typical farfield path loss calculations and so must find the correct forumula to translate PL into distance.

In the meantime, let's estimate that your RXSense = -70 dBm, Ptx=17 dBm, Gtx=-16 dBi, and Grx=-16 dBi.

This means we can afford a path loss of -55 dB.

 

[Harros]

I don't know. Hopefully someone else can answer this question.

What simulation software that you used to simulate the Pierce Oscillator?

 

[Harros]

Again, can we just buy a crystal oscillator to provide the sine wave and do amplification to the output of the crystal oscillator?

**broken link removed**

 

[RadioRon]

Again, can we just buy a crystal oscillator to provide the sine wave and do amplification to the output of the crystal oscillator?

**broken link removed**

Yes, that will work fine.

 

[RadioRon]

What simulation software that you used to simulate the Pierce Oscillator?

I have not simulated this oscillator.

 

[Harros]

Yes, that will work fine.

What differs the crystal oscillator? (as i can see that there are different load capacitance in the crystal oscillator) Any comments on the amplifier that i should build for the crystal oscillator?

 

[Harros]

As for the output filter, your design is ok, but I was thinking of a simpler configuration where L2 and L4 are omitted and C2 and C4 are small value, high impedance. In my simplified configuration, it is necessary to tap into the first resonator made up of L1 and C1 by either tapping into the coil, or using two capacitors to couple in. In this way, the low source impedance does not load the Q of this tank circuit. C2 would be a small value, sufficient to couple energy to L3, C3 which would be resonant. C4 same as C2. The output would also have to tap into the L5,C5 resonator by tapping the coil or by splitting C5 into two values and connecting between them. This type of configuration is simple and easy to tune. You then have three tank circuits that all have high impedance at their tops, and high Q for good selectivity. The loss through such a circuit is reasonably about 2 dB or less.

How to determine the value of the components used (I think i cant build the filter using the lookup table in this case...)?

 

[RadioRon]

How to determine the value of the components used (I think i cant build the filter using the lookup table in this case...)?

Start with this:



then, with focus on parallel resonant circuit, study this:



then this to see how to couple into and out of a parallel resonanct circuit



Then build your model using these principles, plus, when you have three parallel tuned circuits, you can couple from one to the next by using a capacitor at the top of the circuit, but start with a very small value of capacitor, and then gradually increase this capacitor and see the effect on insertion loss and bandwidth.

 

[Harros]

Start with this:



then, with focus on parallel resonant circuit, study this:



then this to see how to couple into and out of a parallel resonanct circuit



Then build your model using these principles, plus, when you have three parallel tuned circuits, you can couple from one to the next by using a capacitor at the top of the circuit, but start with a very small value of capacitor, and then gradually increase this capacitor and see the effect on insertion loss and bandwidth.

Can i use the same filter with the same configuration for the preselect filter and the filter between the RF amplifier and the phase detector?

 

[RadioRon]

Can i use the same filter with the same configuration for the preselect filter and the filter between the RF amplifier and the phase detector?

Yes, but you must adjust each input/output of each filter for a good impedance match.

 

[Harros]

Yes, but you must adjust each input/output of each filter for a good impedance match.

Hi, I have built the BP filter with Q = 1M/70k = 15 approximately, and ~50 ohm for input/output impedance. Any comments on this filter? However the rolloff at upper frequencies seems very slow, will it influence the performance of this filter? Besides, there is a great change of phase response around 1MHz region, will it cause the phase delta measurement to be inaccurate?

 

[mvs sarma]

please look at this,

**broken link removed**

Translation can be done by yahoo translator


All the best

 

[Harros]

please look at this,

**broken link removed**

Translation can be done by yahoo translator


All the best

Thank you for your info, sarma.

 

[RadioRon]

Hi, I have built the BP filter with Q = 1M/70k = 15 approximately, and ~50 ohm for input/output impedance. Any comments on this filter? However the rolloff at upper frequencies seems very slow, will it influence the performance of this filter? Besides, there is a great change of phase response around 1MHz region, will it cause the phase delta measurement to be inaccurate?

The way that you couple the 50 ohm source directly to the input and the 50 ohm load directly to the output is severely reducing the Q of the first tank and the third tank, so the overall filter Q is not good enough. This is evidenced by your measurement of Q which is only 10. This is quite poor and I expect at least 50 and perhaps as high as 200 in the simulation. It will be lower in practice, depending on the Q that you have assigned to the coil in the sim.

Imagine that there is no source attached to the input. In that case, the loaded Q of the first tank circuit might be as high as 50 to 100 or more. However, when you attach the 50 ohm source directly to the top of L1 like that, it is identical to putting a 50 ohm resistor in parallel with L1 which dramatically reduces the loaded Q.

The fact that the rolloff is slow, and levels out, at frequencies above the center frequency of the filter is due to the same problem. As the frequency goes above 1 MHz, the impedance of the top coupling capacitors C2 and C4 goes lower plus the effect of L1, L2 and L3 disappear and so there is nothing with an increasing impedance vs frequency in the way of the energy, so the output levels out at about -50 dB.

The next step to fix these problems is to change the connection point of R1 and of R2. For example, with R1, you should disconnect it from the top of L1 and create a "tap" on L1 about 1/10 from the bottom (that is, 10% of the total number of turns of wire) and then connect R1 to that tap. Similarly, disconnect R2 from C5/L3, create a tap on L3 at the same height as you did for L1, and reconnect R2 there.

This method of tapping the coil will improve the impedance match between the 50 ohm source/load and the tank circuit, it will dramatically increase the loaded Q of the first and third tank, and it will cause the ultimate rejection above resonance to keep going down without levelling out. You may adjust the height of the tap for best overall performance, but it should be kept fairly low on the coil.

The change in phase at the resonant frequency doesn't matter. Ultimately, you will be operating at only one frequency and your circuits will cause a total phase shift of some unknown amount. It will be necessary to calibrate out this phase shift. The important thing is that the phase shift isn't varying with time, and that won't happen in this circuit.

 

[Hero999]

You don't even need to to tap the coil.

Another winding loosly coupled to the coil will do the job - it'll act sa a transformer. In theory you could have the loop outside your house and the coil in front of your bedroom window coupling the energy.