...was thinking for simplicity sake would be nice to get the swr closer to a match without the tuner...
First of all, remember that a tuner matches
impedance, not SWR.
So to know how to match the antenna, you want to know the complex
impedance (preferably in the form R +/- jX) on each band, not just the
SWR.
Despite the current fad for such things, no transformer is going to
give a reasonable match to a 4 : 1 SWR across multiple bands, because
the impedance can vary over a wide range. You need a very different
matching method for 12 ohms, 200 ohms, or 50 -j75 ohms, even though
they all give the same SWR.
Given the low SWR on 160m, it would seem that your wire is close to
quarter wave resonance on 160m, which generally would mean high
impedances on 40m and 80m (depending on the specific frequency).
But that will be transformed by the length of the 75 ohm coax, which
will be close to 1/4 wavelength or so on 40m.
Cutting the wire to 1/2 wavelength on 80m and feeding it as an EFHW
works because then you know the impedance is high on each band of
interest, but only if the matching is performed at the feedpoint rather
than at the shack end of the coax.
With a bit of modeling we can make some estimates as to the
actual impedances you are seeing in the shack, but that will have
to wait until after breakfast and morning appointments...
What I have done in that sort of situation is to build a switched fixed
tuner. That is, I start with a multi-position switch, and build separate
fixed-tuned networks for each band (although I may need to get
more creative to cover most of 80m). This does take a bit of work
to set up, but once done it just requires a flip of the bandswitch
Typically I build a simple L network using a piece of coil stock with
a clip lead for adjustment, and a variable capacitor, to determine the
required matching values. Then I build the
actual unit with an array
of tapped coils and fixed mica capacitors, or sometimes mica trimmers,
as needed for each band of interest. (No, you don't need to build it
as messy as my example!)
In fact, I've used that same unit on at least 3 different antennas over
the last 35 years, by changing coil taps and capacitors when I put up
a different antenna.
Before autotuners were common, many marine radios used this
approach, where the antenna was manually matched (either inside
the transceiver, or in an external box) during initial setup, then the
fixed networks switched as the radio changed channels.
Takes a bit of work, but it is quite easy to use, and, unlike an
autotuner, it permits switching the antenna to different bands
without transmitting.
Author
Topic: using my shortwave rx antenna for tx (Read 323 times)