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Ask Michael, KB9VBR: What is an acceptable impedance level in an antenna

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A viewer asks: What is an acceptable amount of impedance for a 17 foot vertical HF antenna. Joe and I talk about impedance, why you won't always get a 1:1 match, and how that is ok.
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Опубликовано:

18 май 2024

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Комментарии : 6

@BryanBurrma-ex4zr Месяц назад

Absolutely correct here !

@dandypoint 2 месяца назад

Good video. I will add a note from my experience. The impedance at the antenna terminals is a combination of radiation resistance plus total loss resistance. Regarding loss resistance, the omic loss in the antenna is small but the ground loss is quite variable. We will never get to perfect. There will be some loss. The radiation resistance could be around 35 for a quarter wave but will be a lot less for shortened verticals. So with a full size quarter wave vertical, a 1:1 SWR with 50 ohm cable indicates there is some loss. Reducing this loss will lead to the SWR going up a bit. A full size quarter wave vertical with any SWR below 2:1 should be fine for all practical purposes but it does indicate that the ground system could be improved. An SWR of 1.5 or 1.4 is really good. In fact, if the radiation resistance was 35 ohms and we had no loss, the SWR would be 1.4. We also must remember that there are a lot of variables, including the accuracy of our instruments! I can get slightly differing readings between my Bird, Drake and Heathkit meters. So reading a 1.4 on the scale is probably just close to the real number anyway.

@donausmus4281 2 месяца назад

My central Texas QTH requires my Dewalt hammer drill and 3/8" masonry bit to mount the Chameleon spike. Needless to say, I am challenged.

@Ne9n 2 месяца назад

30 years in VFD development. The issues are that the PWM switching is very high (high dv/dt) and any the motor leads can ring like a transmission line up to 1200V. Also, any stray capacitance to ground looks like a good path. The transistors switch a 0- 650 VDC link with rise times up to 10kV per microsecond so frequency components are in the range. The false rise times can cause all kinds of trouble. Motor failures, stray currents on communication links. I learned a lot about AC and RF grounding in that business.

@N5BSB 2 месяца назад

Ground conductivity does make a difference. N5BSB

@KA4UPW 2 месяца назад

Boo Resonances and impetiance are loosely related..please educate yourself before talking.. guy on the left knows guy on the right please get you general liscense