I can't speak directly about Elecraft tuners, but I did design an
antenna tuner when I was at Drake many years ago.
We specified the Drake MN-2700 at 5:1 SWR. I made sure it would match
that SWR at all phase angles on all specified bands.
Typically the low-impedance end tends to be the hardest to match, at
least on the low bands. So 50/5 = 10 ohms resistive is harder to match
than 50*5 = 250 ohms resistive even though the SWR is 5:1 in both
cases. That's because the low impedances need larger tuning
capacitors. The Drake tuner would typically match well above 5:1 into a
high impedance but only barely meet spec into a low impedance. I
suspect the Elecraft tuners are similar.
Alan N1AL
On 7/11/2021 12:58 PM, Al Lorona wrote:
This question is about how manufacturers spec the matching range of their
antenna tuners.
If an antenna system presents an impedance of 5 + j0 ohms to the antenna tuner,
that's an SWR = 10 to 1.
But, an antenna impedance of 50 - j143 ohms is also SWR = 10. So is 110 - j200
ohms.
When a manufacturer like Elecraft says, "Our antenna tuner can match a 10:1
mismatch," does that mean the tuner can match the first case above, the second case,
the third case, or all three?
I guess what I'm asking is, are all of the impedances above equally difficult
for the same tuner to match? Or is one 'harder' than the others? It would
depend on the values of the L and C in the tuner, wouldn't it? Which implies
that certain 10:1 mismatches are not tunable?
Thanks,
Al W6LX/4
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