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Data on 125u Ferrites:
Data on 2000u Ferrites:
SWR Response Data for the same 1.5 MHz antenna but with different ferrite materials.
The 125u material (red line) gives a very narrow bandwidth at 1.5 MHz. Excellent for separating very closely spaced stations: Higher "Q".
The 2000u material (orange line) gives a wider bandwidth at 1.5 MHz. Better for wide bandwidth digital signals: Lower "Q".
Test ferrite rod was VFR15M(125u) and VFR15T(2000u).
Green line is the center point for perfect 1:1 SWR match to 50 ohm load.
100% on graph indicates complete signal loss due to impedance mismatch.
SWR Response Data for the same 500 KHz antenna but with different ferrite materials.
The 125u material (red line) gives a very narrow bandwidth at 500 KHz. Excellent for separating very closely spaced stations: Higher "Q".
The 2000u material (orange line) gives a wider bandwidth at 500 KHz. Better for wide bandwidth digital signals: Lower "Q". This is the maximum recommended frequency for "T" material.
Test ferrite rod was VFR15M(125u) and VFR15T(2000u).
Green line is the center point for perfect 1:1 SWR match to 50 ohm load.
100% on graph indicates complete signal loss due to impedance mismatch.
SWR Response Data for the same 175 KHz antenna but with different ferrite materials.
The 125u material (red line) gives a very narrow bandwidth at 175 KHz. Excellent for separating very closely spaced stations: Higher "Q".
The 2000u material (orange line) gives a wider bandwidth at 175 KHz. Better for wide bandwidth digital signals: Lower "Q".
Test ferrite rod was VFR15M(125u) and VFR15T(2000u).
Green line is the center point for perfect 1:1 SWR match to 50 ohm load.
100% on graph indicates complete signal loss due to impedance mismatch.
SWR Response Data for the same 60 KHz antenna but with different ferrite materials.
The 125u material (red line) gives a very narrow bandwidth at 60 KHz. Excellent for zero-ing WWVB time signal station.
The 2000u material (orange line) gives a wider bandwidth at 60 KHz.
Test ferrite rod was VFR15M(125u) and VFR15T(2000u).
Green line is the center point for perfect 1:1 SWR match to 50 ohm load.
100% on graph indicates complete signal loss due to impedance mismatch.
SWR Response Data for the same 22 KHz antenna but with different ferrite materials.
The 125u material (red line) gives a very narrow bandwidth at 22 KHz. Excellent for zero-ing beacons for solar radio astronomy.
The 2000u material (orange line) gives a wider bandwidth at 22 KHz, useful for general reception.
Test ferrite rod was VFR15M(125u) and VFR15T(2000u).
Green line is the center point for perfect 1:1 SWR match to 50 ohm load.
100% on graph indicates complete signal loss due to impedance mismatch.
NOTE: At 10 KHz, the bandwidths of 125u and 2000u are the same. Below 10 KHz, the 2000u "T" ferrite material begins to have a higher "Q" than the 125 "M" ferrite material.
SWR Response Data for the same 3.4 KHz antenna but with different ferrite materials.
The 2000u material (orange line) gives a narrow bandwidth at 3.4 KHz. (Narrow bandwidth is better for reception of experimental research geo-transmitters).
The 125u material (red line) gives a wider bandwidth at 3.4 KHz. (Wider bandwidth is better for listening to tweeks and whistlers).
Test ferrite rod was VFR15M(125u) and VFR15T(2000u).
Green line is the center point for perfect 1:1 SWR match to 50 ohm load.
100% on graph indicates complete signal loss due to impedance mismatch.
NOTE: At 10 KHz, the bandwidths of 125u and 2000u are the same. Below 10 KHz, the 2000u "T" ferrite material begins to have a higher "Q" than the 125 "M" ferrite material.
Spectral Response Data for the same VLF antenna coil but with different ferrite materials.
125u and 2000u ferrite rod comparison of VFR15 size wound with 800 turns of # 26 magnet wire (total 12 dc Ohms) and tuned to resonance with 0.03uF capacitor. 47 ohms output load resistor.
125u yields 4.100 KHz center frequency. Peak of 23 ohms.
2000u yields 3.300 KHz center frequency. Peak 17 ohms.
Lower ohms value at resonance peak is better for this type of VLF antenna. Ohms value will never be less than the DC ohms value of the wire. In this test example the wire has a DC resistance of 12 ohms. The capacitor also has a small resistance value. Use a non-inductive capacitor.
The 125u material -will- work down to VLF (about 4 KHz like shown), but the peak response is weaker, 23 ohms, and has a wider bandwidth. It is suggested this material best for above 10 KHz where it has much higher "Q".
The 2000u material works well for VLF and has a narrower bandwidth and a stronger peak response of 17 ohms.
Use larger size wire and parallel smaller-value capacitors for less series resistance. Increasing the 47 ohm resistor value will widen the response bandwidth. Decreasing the 47 ohm resistor will further narrow the bandwidth. The VLF receiver using this example antenna will need to be designed to accept input at 17 ohms impedance.
This example antenna is ideal for VLF transmitting using standard audio amplifier outputs of 16 ohms.
Example test of VLF antenna bandwidth control by varying the load resistor.
VFR15T (2000u) wound with 1270 turns of # 30 magnet wire (total 47 DC ohms) and tuned to resonance with 0.03uF capacitor.
47 ohm load resistor. 2.110 KHz center frequency. Peak 27 ohms.
200 ohm load resistor. 2.110 KHz center frequency. Peak 50 ohms.
670 ohm load resistor. 2.110 KHz center frequency. Peak 59 ohms.
1600 ohm load resistor. 2.110 KHz center frequency. Peak 64 ohms.
Example of a 650 ohm (average) Broadband VLF "Whistler" Antenna with cutoff slope at 1200 Hz or above 800 ohms.
VFR15T wound with 1270 turns # 30 magnet wire.
TRANSMITTERS:
WARNING: Frequencies below 50 KHz, if high voltage (more than 30 volts), can cause shock or electrocution. Do not experiment with high voltage. Some voltmeters do not read true voltage at VLF. VLF must be treated like the electricity it is and not like "safe" radio waves.