Jerry,
I was addressing my comments to your application, which I assumed -
maybe wrongly - was a balanced-line-fed multiband doublet.
The balun I referenced is aimed at 160m thru 40m use; but even at the
22MHz low point the choking impedance is still 1,500 Ohms. Note that the
chart shows the **common-mode** impedance of the balun - that is not
related to the differential impedances seen, so you can't assume
anything from that chart about the load seen by a tuner.
In fact, the tuner would see a load little different from that at the
end of the balanced line, because the balun itself comprises a *very*
short series section of balanced transmission line with a Zo of around
150 Ohms. The ferrite core has NO effect on the TL differential-mode
performance.
73,
Steve G3TXQ
On 09/11/2010 18:40, Dr. Gerald N. Johnson wrote:
But Steve, the original post suggesting the balun specifically said 1:4
impedance ratio to transform open line impedances to a better match in
coax where the coax is also far more tolerant to bends and close
proximity to other conducting objects, so the 1:1 may not be all that
suitable.
I notice in the impedance curve of your 1:1 balun there is a series
resonance about 22 MHz where the reactance gets low which is precisely
the condition with a high impedance antenna where a tuner could tune to
the balun, not the antenna.
73, Jerry, K0CQ
On 11/9/2010 4:14 AM, Steve Hunt wrote:
Jerry,
That shouldn't happen with a well-designed 1:1 Guanella Balun, which is
the preferred choice for wide-band, wide-impedance-excusion,
applications. Unlike a 4:1 Guanella balun or 4:1 Ruthroff balun, the
core flux in a 1:1 Guanella balun is not determined directly by the load
impedance / differential-mode voltage.
Here's an example of what I mean by a well designed 1:1 Guanella balun:
http://www.balundesigns.com/servlet/the-98/isolation-choke-balun-common/Detail
73,
Steve G3TXQ
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