



(This test data below reflects our "VFR" part numbered ferrite rods. New data will be collected on our "V2R" part numbered 2000u high conductivity ferrite rods, which are a product improvement).
Bandwidth response of same antenna coil tuned to different frequencies using 2000u ferrite rod. Only the capacitance value was changed (from 384 pF to 9 pF range) to resonate center for 1:1 SWR.
Bandwidth (channel width) narrows as frequency decreases. 2000u ferrite rods operate best below 500 KHz. 2000u ferrite rods will work down to DC 0 Hertz. This graph shows tests performed on a 4.5 inch X 1 inch ferrite rod at longwave (LW) band frequencies of 500 KHz, 400 KHz, 300 KHz, 200 KHz, and 160 KHz.
125u standard material operating below 10 KHz will give a moderate impedance result ( 62000 ohms in example ). Resonant frequency is @ 3725 Hz.
2000u standard material operating below 10 KHz will give a high impedance result ( 94000 ohms in example ). Resonant frequency is @ 2900 Hz.
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.
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.
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.
The 125u material (red line) gives a very narrow bandwidth at 60 KHz. Excellent for zeroing 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.
The 125u material (red line) gives extreme narrow bandwidth at 22 KHz. Probably too narrow to use due to circuit drift, but interesting.
The 2000u material (orange line) gives a slightly wider bandwidth at 22 KHz, useful for general reception and excellent for zeroing beacons for solar radio astronomy.
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.
The 2000u material (orange line) gives a narrow bandwidth at 3.4 KHz. (Narrow bandwidth is better for reception of experimental research geotransmitters).
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.
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 noninductive 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 smallervalue 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.
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.
VFR15T wound with 1270 turns # 30 magnet wire.
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.