Help with Resonance frequency

[Henrikras]

Dear guys.
I just made the test on the Stock coil, to get the resonance before I start to winding a new 13" coil.

At the TX it got nicely 25,6 khz.... BUT at the RX it was only 18,0 khz !!!! That I dont get.. The RX is connected to the little board with a amplifirer, but even with that i mind, I can't get that this should raise the frequency up to 25 khz.
I've change the capacity down to 2,2 nf, and I went up to 58 khz.
Could it Be that the manefactor should had used not the 22nf as it is, but something like 15-16 nf.?
Or do I overlook something...!

Please help me.
Thanks.
Ps Sorry that the picture is 180 deg. Turned... I dont know how to turn it back.
Henrik

[Skippy]

Blimey Hen, you don't make this easy for us! Do we have to guess this is about the Deeptech Vista Gold 25KHz coil you are copying? Upside down photos that are three times larger than my PC screen? Come on fella, keep the pics down to 800 pixels width, get a download of IrfanView or something....any way, back on topic, the RX will not be tuned to the TX frequency, it will be 10 - 25% higher or lower in frequency, depending on the designers choice. In this case, 25% lower seems the answer. Others will have more detailed explanations why, but matching TX and RX resonances seems to cause stability and discrimination problems. Putting 2n2 across the RX coil will raise the resonant frequency by square-root of 10 = 3.162, giving 18 x 3.162 = 57KHz, so this test was a correct result too. In summary, your measurements are correct, I think.

[Henrikras]

Thanks Skippy... you Helped some much. I would try to get same uH and R and resonans, makeing the new coil.
Sorry all your trouble..
Henrik

[Henrikras]

I learned some more today.... To find resonance I did a test on 4 different coils. All TX was Very close to 1mH. That was interesting.
Vista Gold 25 khz 11" TX (2,4 ohm) with 45 nF = 25,6 khz = 900 uH .(0,9 mH)
Blisstool 8 khz 11" TX (2,6 ohm) with 45 nf = 23,7 khz = 1020 uH .(1.02 mH)
Blisstool. 8 khz 15" TX (3,7 ohm) with 45 nf = 23,7 khz = 1020 uH .(1.02 mH)
Teroso. 14,5khz 10x12"(4,4ohm) with 45 nf = 24,5 khz = 955 uH .(0,955mH)

I double tjek with a 65nf and all gave same results. I tells me that many VFL coils got approxly 1,0 mH. (+-)
The RX was a bit different... Vista Gold RX = 3,5 mH and the Bliss both coils 8,8 mH.
That's make me think that the RX need to in balance with LC size to get the best out to a resonance frequency, but the TX is more important that the R is in balance, and the "C" can Be changed a lot to get resonance.

What do you think about my theory ?

Ps. This was a great help...http://www.siversima.com/rf-calculat...FfB3cAodsAgAzg

Henrik