Thank you for your questions and observations.

If I have not made a mistake of some sort, this describes delivery of power to the antenna in original MK-X1 circuit:

For example, say the oscillator output is sourcing 16 mA at 2 V at 1.228 MHz and using the prescribed 220 uH for L2.

Then 16 mA x 50% duty cycle = 8 mA effective current.

If the load on the oscillator output was a resistor, 2 V x 8 mA = 16 mW of power would be supplied.

In the original circuit, L2 and C6 plus the antenna capacitance are a series resonant circuit. The current supplied from the oscillator

is determined by the oscillator source resistance and the resistive component of the L2 - C6 - antenna circuit.

The current through L2 of the original circuit divides among C6 and the antenna according to the reactances.

L2 = 220 uH, gives 1704 ohms Xl, 8 mA x 1704 Xl = 13.6 V

C6 + antenna = 76 pF, gives 1704 ohms Xc, 8 mA x 1704 Xc = 13.6 V

Antenna = 26 pf, gives 4981 ohms Xc, 13.6 V / 4981 ohms = 2.73 mA, 34% of 8 mA.

At 2 ohms radiation resistance (Rr), 2.73 mA gives 15 microwatts (uW) radiated.

C6 = 50 pF, gives 2590 ohms Xc, 13.6 / 2590 = 5.25 mA, 66% of 8 mA. This is not passing through Rr, so 128 uW is wasted.

If the dc resistance of L2 is 5 ohms, 320 uW is dissipated in L2.

(15 uW / 16 mW) x 100 = 0.0937 % efficiency. Almost none of the oscillator power is used to produce radiation.

hwhall wrote:

L2 & C6 look like an L-match which has long been used to feed electrically short antennas. I notice the

http://www.ittc.ku.edu/ reference doesn't say anything about L-matches dissipating power as heat.

The original L2 - C6 circuit does not act as an impedance matching L network because, in the 1.228 MHz case, to do so would require that the

oscillator output have 3500 ohms of inductive reactance and much less resistance than the antenna Rr, and the antenna would need to have

100 ohms Rr and 15,000 ohms inductive reactance.

Yes, the reactive components of the output network, for the most part, do not dissipate power.

I was thinking that more power would be dissipated in the oscillator final RF stage transistors with the original antenna coupling circuit

than with the proposed L network but that is not the case.

If the proposed L network with C6 on the input end of L2 is used, much more power will be delivered to the radiation resistance

because the reactance of the antenna is counteracted and the antenna is the only thing that the current from the network can pass through.

The oscillator will be driving a resistive load (current in phase with voltage) of much higher resistance than with the original circuit.

As in any other tuning circuit, the variable capacitance C6 and inductance L2 are intended to compensate for some variation in antenna characteristics.

No, I have not wired up the suggested antenna coupling circuit but it is nothing new.

I don't have facilities to try wiring up circuits at this time.

Addendum: With the original L2 - C6 - antenna output network, the oscillator output must be acting substantially as an

amplitude modulated current source because the output network L2 - C6 - antenna is resonant and has very little dc resistance.

I think that the current from the oscillator is determined by the modulated power supply voltage, the collector - emitter

resistance of the output transistor(s) and the resistance within the oscillator in series with the collector of the output transistor(s).

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WB5HDF