What is the differents between a TR and VLF ?

[Hunter Joe]

I live in Florida and the TR circiut works very good here. I know some machine have had both in one machine. I know the coils are pretty much the same.I was trying to firgure out if a VLF can be converted to a TR with out changing the whole board?. Thank you ,Joe

[diggerbarns]

To begin with there was the BFO that was a bit of a pig to use and did not go very deep at all, but was cheap to buy.

Then there was IB ( Induction Balance ). This was a great improvement over BFO and things really took off. Ther were lots of different coil arrangments. 4B, IB, 2D, Concentric,
Coplanar. 2D was about the best and a lot simpler to make so became the most popular for a while. Nowdays Concentric ( POLO ) are most popular, probably because they are the simpler to mass produce. TR is just a marketing term someone dreamed up does'nt mean anythig. 1st IB,s worked at about 100khz or higher. It was soon found that lower freq was better 5 to 20 khz is common these days. Marketing man said " LET THERE BE VLF " TR and VLF can be the same or not the same. TR and VLF don't really mean anything. TR = Total-Response or Transmit-receive. VLF = Very Low Frequency.

[Carl-NC]

Digger is right... TR = VLF = IB, for the most part. VLF is the radio band from 3kHz to 30kHz, so any detector operating in that range is VLF, even if it is a BFO. And, when you think about it, PI detectors are TR as well, perhaps even more so than IB.

- Carl