The AM Forum

Here is another problem I can't seem to solve:

I built the pictured tuner a couple of months ago using surplus parts that I have collected over the past few years. 

One thing baffles me though, it is a simple "T" configuration with the "L" going to ground between the input capacitor and the loading capacitor.

It does not work! Not as anticipated at least.

If I put my "aerial analyzer" on the input side and a known 50 ohm resistive load on the output side I cannot adjust the unit to better than 1.5:1 at any frequency.  I always end up with some reactive component and some resistive component... never can I adjust it to 1:1 SWR and 50 ohms resistive and 0 ohms reactive.

Am I expecting too much of the thing or is there some inherent error in my thinking about this?

Thanks, Tom

Really nice looking tuner.   You have a pure 50 ohm load, no need for a tuner.  Probably, you're not able to tune out the reactance in the tuner itself.  Maybe recheck that the circuit is wired the way it should be.  I can't tell from the pics how it's wired.  Also connect your load directly to the test analyzer to see if you get a lower SWR.

Part of your problem is that you're using an aerial analyzer, you need to use an antenna analyzer. ;D

Fred

have you tried several frequencies ?    say at least 80/40/20 meters .... are you using the plain "T" match or the ultimate match circuit ?

there's nothing wrong in using a 50 Ohm load as a test .... a reasonable starting point

Tom,

I have found that matching 50 ohms unbalanced to a load that is near 50 ohms unbalanced can be a challenge sometimes.  This is a common match between a transmitter and a coax fed dipole.   I, too, had trouble getting a perfect 1:1 match using the T only at times.

I found the solution was to have two configurations.  I use a T config like yours - but in addition I can switch it to a pi-L configuration.  This is with L in and C1 connected to the other end of L and then to ground.  Or use a standard pi-network with two caps and a coil for the second config.

These two configs will match most any 50 to ~20-200 ohm unbal-unbal situation.   Just takes two or three extra switches and you're golden.

I use these 50 ohm flexible configs to match all of my amplifier inputs as outboard fine tuning.

T

Thanks for the reply.  My biggest fear was that the "thought process" of my testing was way off.  Since building my antenna "aerial" analyzer I have run into more questions than answers in using it....  In some ways the "load it until the plates turn red" were more satisfying than trying to achieve some semblance of "perfection"!

73, Tom

Assuming the output cap is on the left and the input cap is on the right, it looks like the regular design and should do well. What max value is the input cap per section? 300-400pF?

Is it like the circuit attached?

The diagram is attached....  it is not like the one you show.  Do you see a fundamental issue?

Tnx, Tom