For some strange reason I've gotten into making audio recordings of nature the past few weeks. Sometimes I want to stick a Raspberry Pi and battery and sound card out there, sometimes I like the simplicity of analog. You can buy some decent electret capsules for 10 cents each on Aliexpress so I built up some preamps to get them to line level. I lug my laptop out to the garage and plug in a USB soundcard and record until the battery goes dead (wall wart has too much hum and trash to use that).
At my job before I retired I grabbed a bunch of 40 ft. pieces of RG-59 coax out of a recycle pile. You can power an electret Sound Blaster style with it at the far end of the coax while you power it and pick off signal at the other end. The effect of the coax's per foot capacitance on high frequency response isn't so easy to predict.
But a long coax isn't a nice balanced line. I did some recording with electrets and preamps and coax 40 years ago and it sort of worked. But one night when everything was quiet I could hear a shortwave station coming in on it. And there was other trash as well. Recently I figured out that the shield acts as an antenna while the inner conductor is the other part of the circuit, the voltage ends up going into your amplifier.
So I was wondering if this would work. I know hams with balanced antenna lines (ladder line) can run short stretches inside coax like if they need to go through a culvert or something. I think it doesn't matter that it's not balanced here, it's still going to be shielded by the braid. If the outer braid picks up an RF signal it won't matter because it's not connected to anything anyway, it's just keeping the RF off the inner wires.
At my job before I retired I grabbed a bunch of 40 ft. pieces of RG-59 coax out of a recycle pile. You can power an electret Sound Blaster style with it at the far end of the coax while you power it and pick off signal at the other end. The effect of the coax's per foot capacitance on high frequency response isn't so easy to predict.
But a long coax isn't a nice balanced line. I did some recording with electrets and preamps and coax 40 years ago and it sort of worked. But one night when everything was quiet I could hear a shortwave station coming in on it. And there was other trash as well. Recently I figured out that the shield acts as an antenna while the inner conductor is the other part of the circuit, the voltage ends up going into your amplifier.
So I was wondering if this would work. I know hams with balanced antenna lines (ladder line) can run short stretches inside coax like if they need to go through a culvert or something. I think it doesn't matter that it's not balanced here, it's still going to be shielded by the braid. If the outer braid picks up an RF signal it won't matter because it's not connected to anything anyway, it's just keeping the RF off the inner wires.