Antenna Tuning

[W6HSA]

Is it more ideal to have a higher capacitance on the transmitter side than on the antenna side 'in principal' when tuning an antenna? Secondly, is it better to have a higher or lower inductance? I understand the obvious answer: "whatever achieves the best SWR with the best forward"; however, this question came up in last night's discussion and it was centered on the electrical question rather than the empirical answer. My position was a higher capacitance on the radio side was better and a lower inductance was best.

I realize the answer is obvious: once one achieves the right SWR so maybe the question is irrelevant.

 

[Captain Kilowatt]

Is it more ideal to have a higher capacitance on the transmitter side than on the antenna side 'in principal' when tuning an antenna? Secondly, is it better to have a higher or lower inductance? I understand the obvious answer: "whatever achieves the best SWR with the best forward"; however, this question came up in last night's discussion and it was centered on the electrical question rather than the empirical answer. My position was a higher capacitance on the radio side was better and a lower inductance was best.

I realize the answer is obvious: once one achieves the right SWR so maybe the question is irrelevant.

Irrelevant? No. Completely misunderstood? Yes. I do not follow what you mean by " have a higher capacitance on the transmitter side than on the antenna side" . Do you mean the values of the components in an antenna tuner or are you talking about tuning the actual antenna itself by making adjustments to the antenna? If it is the former then the value will depend on the impedance trying to be matched and you always want the least amount of inductance. That allows for broader bandwidth without the need to retune and less losses in the loading inductor. If you meant the latter, you always want zero capacitance and zero inductance as that constitutes reactance which affects power delivery to the antenna.

 

[W6HSA]

Irrelevant? No. Completely misunderstood? Yes. I do not follow what you mean by " have a higher capacitance on the transmitter side than on the antenna side" . Do you mean the values of the components in an antenna tuner or are you talking about tuning the actual antenna itself by making adjustments to the antenna? If it is the former then the value will depend on the impedance trying to be matched and you always want the least amount of inductance. That allows for broader bandwidth without the need to retune and less losses in the loading inductor. If you meant the latter, you always want zero capacitance and zero inductance as that constitutes reactance which affects power delivery to the antenna.

Ah, excellent, thanks. I indeed meant the former; that is, using an antenna tuner (sorry, I didn't make that clear). I always thought lower inductance was better, although admittedly I did not understand the broader bandwidth aspect, and capacitance tuning would then follow the lowest inductance. I believe the capacitance value presented to the radio (the transmitter tuning capacitor) will be higher in this instance, which I always understood to be 'better'. Not sure that's the case either. At any rate, I am able to get the lowest SWR with the lowest inductance and 'reasonable' capacitance and that is the bottom line.

Thanks again, for answering.

 

[Marconi]

Ah, excellent, thanks. I indeed meant the former; that is, using an antenna tuner (sorry, I didn't make that clear). I always thought lower inductance was better, although admittedly I did not understand the broader bandwidth aspect, and capacitance tuning would then follow the lowest inductance. I believe the capacitance value presented to the radio (the transmitter tuning capacitor) will be higher in this instance, which I always understood to be 'better'. Not sure that's the case either. At any rate, I am able to get the lowest SWR with the lowest inductance and 'reasonable' capacitance and that is the bottom line.

Thanks again, for answering.

Hey W6HSA, I don't understand your point. Can you give us some details how you determine, test, and adjust such issues that show the results you're talking about?

 

[Captain Kilowatt]

Ah, excellent, thanks. I indeed meant the former; that is, using an antenna tuner (sorry, I didn't make that clear). I always thought lower inductance was better, although admittedly I did not understand the broader bandwidth aspect, and capacitance tuning would then follow the lowest inductance. I believe the capacitance value presented to the radio (the transmitter tuning capacitor) will be higher in this instance, which I always understood to be 'better'. Not sure that's the case either. At any rate, I am able to get the lowest SWR with the lowest inductance and 'reasonable' capacitance and that is the bottom line.

Thanks again, for answering.

Whether you have more capacitance on the transmitter side or the antenna side will depend on the impedance ratio of the antenna.You generally need more capacitance on the side of the tuner that has the lower impedance therefore if the antenna is low impedance you will need more cap on the antenna side of the tuner but if the antenna is high impedance you will need more cap on the transmitter side. Either way it is moot as you simply tune the knobs for lowest SWR and not worry about which side has more cap.