Can a resister be added to correct frequency on a coil?

[pito]

Low Rx coil resistance is reducing thermal noise and is increasing coil Q. High Q coil = less interferences, more unstable to temperature changes.

[Carl-NC]

I would a heavier guage wire on Rx give me less sensitivity? How low can I go on resistance on the Rx?

You can go all the way to zero ohms if you like, but it won't help any. The Tejon series-resonates the RX coil with a 4.7k load resistor¹ so even 100Ω of coil resistance will work. Anything less than 100Ω will also work, and not any better except for thermal noise. For thermal noise, the Tejon has a 120Ω feedforward resistor so keeping the RX coil resistance under 60Ω will minimize its contribution. And, that's about where the stock coils are at. Feel free to use a larger wire gauge if you like, but it only makes the coil heavier.

¹ This load resistor sets the Q, the coil resistance has almost no effect.

[pito]

Low turn numbers coils have low Q - that is for Tx coil driven by square wave,

[kac]

So for a 300mm d concentric I came up with:
Tx = 36 Tuns of 26 awg, 9 of which will be the Bx approx
Rx 218 turns 30 awg

Sound about right?

[Carl-NC]

Yup, sounds pretty good.

[kac]

So far the coil is coming along but ran into an issue with the Tx. I used 26 guage and according to the coil calculator i should have been at 4 ohms but instead I end up with 5 ohms. The Rx came in with spec according to the calculator. I had a similar issue with an elliptical I was working on with Tx being way out of spec. I took a mic to it and 26 awg is supposed to be 0.0159" but the spool I have is 0.0163".
Would too much resistance cause the machine just to sound off when hooked to it as if it had a broken connection? I have continuity with rx, tx, even through my cable and cable has a new connector. Machine works as it should with stock coils.
Here is the frame I made to wind on. It mounts to a piece of mdf that I mounted to my winding machine. Plan is to do my winds on this then mount it inside a printed housing. Since fdm printed parts have a grain to them from their layers to make this durable I will make a separate coil ears that will mount to the housing and bolt in with plastic bolts making them also replaceable. This allows me to print the housing upside down so there is no supports required and no cleanup. Similarly the winding frame also does not require any supports.
All goes well I should be able to make a few and keep them consistent.

[kac]

Out of curiosity I took the shielding off the wire and it specs to 0.0155" with shielding 0.0163". Precision wire specs say 0.0159".

[Carl-NC]

Wire appears to be within a reasonable spec. An extra ohm is not going to make the coil not work. At worst, it will slightly shift the GB preset and might cause some GB drift over temperature. I would not worry about it.

[kac]

What would cause the machine just to sound off then when it's hooked to the coil? Is it just way out of phase?

[Carl-NC]

Don't know. With the coil connected, does the detector just sound continuously? How good is the null?

[Smirnov-Arta]

This is a resonant circuit, and its stability is not an easy task. Unfortunately, it depends not only on the quality factor of the contour. It is also worth taking into account the own capacity of the coil, "tke" of capacitors, the capacity of the sensor cable, etc. The quality factor of the coil, as you know, can be obtained in various ways, for example, by increasing the diameter of the wire or increasing the number of turns and reducing the diameter of the wire. That is, the correct selection of all these and other parameters will be able to give a good result.

[kac]

Found a couple of things. First off I was using a very old original Tesoro cable and it may have had a break in the shielding somewheres so it would have a short. I replaced that with fresh cable I had purchased before which had 4 wires + ground. I don't need the ground as this is a delta coil. Tinned the ends and put the connector on and added some potting in between on connector to make sure there are no shorts.

Still had the fault so for kicks I swapped wires and it works. Turns out the wires were marked wrong on the info I had picked up off the web. Tx and Rx were on wrong pin #'s.

Coil isn't half bad as I have it but will hook the scope up and fine tune it best I can.

Tx should be pins 4 and 2, Rx is 3 and 1. Pins 2 and 1 are returns as far as I can tell.

[Carl-NC]

Still had the fault so for kicks I swapped wires and it works. Turns out the wires were marked wrong on the info I had picked up off the web. Tx and Rx were on wrong pin #'s.

Yup, that'll do it.