[ARC5] Rollerductor setting

[Brian]

Some issues to consider:

  a.. Nowhere in your line-up is there a measure of line impedance. Many Wattmeter designers assume a 50 Ohm line, and so, for economy, read either the current or the Voltage – these ones have a linear scale. Bird Wattmeters are designed for specific line impedances. Walter Breune (one of Art Collins’ designers) came up with a Wattmeter design that multiplied in-phase current and Voltage, and so, was independent of line impedance; this design appears, for instance, in the TRC-75. This design was copied by General Dynamics for use in the GRC-106. 
  b.. A similar issue applies to your unun; these need to be designed for a specific transmission line impedance. Merely putting it in line with coaxial cable does not convert both sides of the unun to the impedance of the coax. 
  c.. Coax to a dipole? This means that the outer conductor of your coax is part of the antenna, is unbalanced, and so the currents in the inner and outer are probably different. If you want to use a unun, then it should be at the feed point of your dipole. But we have no idea of the feed-point impedance of your dipole – we can only assume it is somewhat balanced.

73 de Brian, VK2GCE

On Sunday, April 23, 2017 2:11 AM, J McVey said:

Good question. I was not clear on the setup.
The setup is a s follows:

Tx -> cap -> BC-442 (ammeter) ->unun -> coax-> wattmeter-> coax->dipole

The low current is in the unun lo-z primary.

The over-all Z is probably higher because the the reflected antenna reactance becomes part of the primary circuit too.
Interesting stuff...




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