[HCARC] Loop Questions
Gary J - N5BAA
qltfnish at omniglobal.net
Thu Jul 2 16:40:37 EDT 2015
"The frequencies quoted in the last paragraph are obviously MHz not kHz."
Without doubt - I just cut and pasted them there without looking at them.
Mentally I knew what they were saying.
For Lew King - The loop we used at FD turned out to be approx 562 feet in
length. Working backwards from the formula we should be able to calculate
what our resonant points should have approximately been.
http://www.n1wpn.net/loop_antennas_and_calculator.htm
562 feet gives 160- 1.788 mhz, 80 - 3.576 mhz, 40 - 7.152 mhz, 20 -
14.304 mhz 10 - 28.608 mhz
A few extra feet might have made a big difference:
565' is comfortably resonant at 1.778 mHz, 3.557 mHz, 7.115 mHz, 14.230 mHz
and 28.460 mHz.
574' is comfortably resonant at 1.75 mHz, 3.5 mHz, 7.00 mHz, 14.000 mHz and
28.000 mHz
Gary J
N5BAA
-----Original Message-----
From: Kerry Sandstrom
Sent: Thursday, July 2, 2015 12:49 PM
To: Gary J - N5BAA ; HCARC Reflector
Subject: Re: [HCARC] Loop Questions
Gary,
What counts is the impedance at the transmitter end of the transmission
line. The impedance at the transmitter end depends on the impedance at
the loop feed point, the impedance of the transmission line and the
length of the transmission line in wavelengths. It is unlikely that the
impedance at the transmitter end is 450 Ohm. The way you figure out the
impedance is using the complex feed point impedance of the loop and a
Smith chart. Since the length of the transmission line in wavelengths
varies with frequency, the impedance at different frequencies is likely
to be wildly different. No matter which balun you use, they will still
be wildly different and seldom close to 50 Ohm.
The purpose of the copper-clad steel wire is purely for strength. That
type of wire is typically called "Copperweld" after the manufacturer.
Solid copper wire is not as strong and will stretch under tension. If
you need strength, then you need to use the Copperweld type wire. The
impedance of the line has very little to do with the material used. The
difference between the 400 Ohm line and the 450 Ohm line is because of
differences in wire size or spacing. The way Copperweld wire is made is
by pulling a couple ribbons of copper with a steel wire in the middle
through a die. I had a trip to the factory in TN many years ago when I
was purchasing $100K worth of Copperweld wire and learned quite a bit
about the process!
The frequencies quoted in the last paragraph are obviously MHz not kHz.
On 7/2/2015 12:18 PM, Gary J - N5BAA wrote:
> Lew, Frank, Dale and Gale,
>
> Why is it that when using 450 ohm ladder line to feed a loop to the radio
> are we are using a 4:1 balun instead of a 9:1 balun??
>
> BTW, what type of ladder line is best?? I have seen copper clad steel at
> 400 ohms and pure copper from Davis at 450 ohms with the all copper being
> cheaper than the copper clad steel – go figure.
>
> For Dale, Gale and anyone else who does modeling: Can you model Loops at
> approx 50-60 feet above ground?? It would be nice to know the best loop
> length for resonant points in the 160/80/40/20/15 bands for use at Field
> Day. I.e. what length gives us the best choice of resonant frequencies.
> The loop skywire website (http://n1su.com/loop.html) gives the following:
>
> a.. 565' is comfortably resonant at 1.778kHz, 3.557kHz, 7.115kHz,
> 14.230kHz and 28.460kHz.
> b.. 574' is comfortably resonant at 1.750kHz, 3.5kHz, 7.00kHz,
> 14.000kHz and 28.000kHz
> Is there a longer length that might even do better?? What might 1130 feet
> look like?? As you can tell – I don’t know squat about loops.
>
> Gary J
> N5BAA
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