|[AMRadio] antenna tuners transmision lines and more|
k4kyv at hotmail.com
Tue Apr 25 19:32:12 EDT 2006
>From: "John E. Coleman (ARS WA5BXO)" <wa5bxo2005 at pctechref.com>
>I have seen
>toriods used in HF tube type equipment also but they still have tuning. I
>was speaking of rigs with no internal tuning for the final amps. Most
>modern solid state equipment is this way. This type of equipment that has
>no output tuning must have a specific non reactive load attached or it will
>not work as specified by the manufacture. This is where external tuning
>equipment is necessary because it is very difficult to get an antenna to be
>non reactive and represent a 50 ohm load. And should you achieve this then
>it would only be for a small range of frequencies. Where as, if you had a
>rig with adjustable output circuitry such as a Pi-Net with a loading and a
>plate tune knob then you would be able to match a much larger range of
>frequencies even though the VSWR on the coax line may be as high as 2:1.
What it boils down to is that with classic tube type rigs, the rf tank
circuit was built into the rig. With modern solid state rigs, the rf tank
circuit comes as an external option that you have to pay extra for.
I recall there was a Central Electronics rig that had a no-tune broadband
output network with a tube type final. They sealed the whole thing in
something like epoxy, and gave no technical data on how it worked. I recall
reading an article in CQ or 73 Magazine about how someone unsuccessfully
tried to disassemble one of the networks to find out how it worked, and
ended up with "probably the only (Central Electronics rig) with a tuneable
pi-network tank circuit.
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