[Elecraft] Question about antenna matching

[David Gilbert]

Hi, Al.

Yes, some mismatches are much more problematic than others, even for the 
same SWR.

One way to see this is to use TLW, the transmission line calculator that 
comes free with the ARRL Antenna Book.  Choose whatever load impedance 
you want in any combination of real and reactive values. Click the 
"Tuner" button to see various options for the tuner configuration and 
then set the Q for the capacitor(s) and coil to whatever you think is 
reasonable  The most common configurations would either be high pass 
L-Network or high pass T-network.

Not only will you see a diagram of the tuner with the required values to 
give a match, but you can see the voltage, current, and power loss 
(heating) for each component.  Try different load impedance combinations 
to see the different power losses.  The difference can be striking.

In general, low impedances will cause more tuner loss than higher 
impedances, and capacitive load reactance tends to be more problematic 
than inductive reactance.  That, of course, is mostly because real life 
inductors tend to have lower Q than capacitors, and that is certainly 
the case for auto tuners with ferrite core inductors.

As an aside, TLW is an amazing tool and most people don't give it the 
credit it is due.

73,
Dave   AB7E



On 7/11/2021 11:58 AM, 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