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Author Topic: NR16020 second world flight dorsal V antenna  (Read 45411 times)

Chuck Varney

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Re: NR16020 second world flight dorsal V antenna
« Reply #30 on: January 13, 2011, 05:46:00 PM »


The project was far from trivial, but it was greatly facilitated by the excellent tools in 4NEC2, and the detailed dimensions in the Harney drawings.  

Bob,

I'm nearly non-conversant with 4NEC2, but I used its Geometry Builder tool a couple years ago to build some objects to fly the dorsal V on. In the wee hours this morning it occurred to me that you may have used the same tool to build your Electra wire frame. Did you?  

Quote
The impedance at 6210 kHz is 5.73 - j0.42 ohms, with the loading coil set to 10.6 uH, and a 50 pF series capacitor.

To stay on topic yesterday I didn't ask, but I'm curious as to what motivated the use of 50 pF as the series capacitor for 6210 kHz? Why didn't you use the optional 62.5 pF capacitor cited in Morgan for the WE 13C? Using it and 8 uH would reduce + j 98.6 to + j 0.7 (and 7.98 uH would essentially nullify it).

Chuck
« Last Edit: January 13, 2011, 05:47:40 PM by Chuck Varney »
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Bob Brandenburg

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Re: NR16020 second world flight dorsal V antenna
« Reply #31 on: January 14, 2011, 09:20:22 AM »

Bob,

I'm nearly non-conversant with 4NEC2, but I used its Geometry Builder tool a couple years ago to build some objects to fly the dorsal V on. In the wee hours this morning it occurred to me that you may have used the same tool to build your Electra wire frame. Did you?  

Yes.

Quote
To stay on topic yesterday I didn't ask, but I'm curious as to what motivated the use of 50 pF as the series capacitor for 6210 kHz? Why didn't you use the optional 62.5 pF capacitor cited in Morgan for the WE 13C? Using it and 8 uH would reduce + j 98.6 to + j 0.7 (and 7.98 uH would essentially nullify it).

Chuck

Morgan doesn't specify 62.5 pF.   He says that "occasionally it will be found that the series condenser s supplied will not give correct operation, and a 62.5 mmf condenser may be used."

The context of his discussion covers two options:  a nose-to-tail 40 foot wire, or a 70 ohm transmission line with tuning unit.   Neither of the cases applied to the Electra, and we don't know exactly what capacitors were used for 3105 and 6210 in the Electra installation.  So I made a conservative assumption in both cases.   Since tuning the transmitter was accomplished by adjusting the loading coil, it follows that the design intent was for the unloaded antenna to be capacitive at the operating frequency.  Using 50 pF at 6210, less than the minimum Morgan suggests for the two cases he discusses, seemed a reasonable way to force the unloaded antenna to be capacitive at that frequency.

Bob
« Last Edit: January 14, 2011, 04:58:52 PM by moleski »
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Chuck Varney

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Re: NR16020 second world flight dorsal V antenna
« Reply #32 on: January 14, 2011, 03:36:31 PM »


Using 50 pF at 6210, less than the minimum Morgan suggests for the two cases he discusses, seemed a reasonable way to force the unloaded antenna to be capacitive at that frequency.

OK, thank you, Bob. With the reactive term of the antenna input impedance at + j 98.6, a series 250 pF would make it marginally capacitive, so your jumping beyond 125 pF and 62.5 pF to 50 pF prompted the question.

Chuck
« Last Edit: January 14, 2011, 08:32:30 PM by Chuck Varney »
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