HFU HF Underground
Technical Topics => Equipment => Topic started by: Jason on September 02, 2018, 1346 UTC
-
So, I've got a 7'- 1/2"dia piece of coax
RX only
Cable Impedance 50 ohm ±2 ohm
Capacitance 23.0 pF/ft | 75.5 pF/m
dc Resistance, Inner Conductor 1.476 ohms/km | 0.450 ohms/kft
dc Resistance, Outer Conductor 1.903 ohms/km | 0.580 ohms/kft
dc Test Voltage 4000 V
Inductance 0.190 µH/m | 0.058 µH/ft
Insulation Resistance 100000 Mohms•km
Jacket Spark Test Voltage (rms) 5000 V
Operating Frequency Band 1 – 8800 MHz
Peak Power 40.0 kW
Power Attenuation 2.325
I would like the bandwidth as wide as possible; I like 40m & 80m. Parts, tuner, capacitor ? Good cost efficient idea's requested.
-
Are you asking if you can use the coax you have as the loop itself? if so it should work, but the characteristics as coaxial cable don't really matter. I would just be a fat copper wire.
do you need a fixed frequency? or tuneability? Wide bandwidth is fairly easy to attain if you are willing to re-tune when changing frequencies, but quite difficult if you don't want to adjust the cap.
Are you looking to transmit? or just receive? a circumference of 7 feet isn't really enough to build an effecient magnetic loop for frequencies below 20 MHz, but for RX only you would be fine.
for 80 meters, a good magnetic loop for transmitting would have a circumference around 30 feet (diameter around 10 feet) and need several hundred Pf of tuning cap rated for about 100 volts per watt of input power.
Of course, this data goes for transmitting, To just receive, don't bother with a single turn loop, use a 2 to 5 turn loop (or more if you want it to be smaller) and a tuning cap from an old am radio. you will still need to tune as you move across the band
-
https://www.w8ji.com/magnetic_receiving_loops.htm