# On-line T-match calculators give weird answers???

Discussion in 'Antennas, Feedlines, Towers & Rotors' started by WA7ARK, Oct 15, 2020.

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1. ### WA7ARKHam MemberQRZ Page

50 Ohm source at 1.85MHz

Load to be matched is 23 - j813 Ohms

I am trying to find required values for the source-side C, the shunt L, and the load-side C for a standard T-network as found in desktop tuners.

Using most of the on-line calcs, like this one, I get negative values for the capacitors.

What is going on???

I do not have SimSmith on this computer.

2. ### AC6LAHam MemberQRZ Page

With that load at 1.85 MHz a huge inductor is required.

Dan, AC6LA

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3. ### WA7ARKHam MemberQRZ Page

Thanks Dan,

Using my wife's laptop computer. All I have here is bare-nekkid EzNec.

That is probably why my friend cannot match his ladder-line fed, non-resonant, 425ft horizontal loop using his desktop tuner on 160m.

That is a lot of loss in the tuner.

I am going to add a coil in the loop wire to see if I can cancel some of that reactance before the tuner sees it.

How far would I have to reduce the -j term so that an normal T-tuner with 25 to 30uH could handle it?

Tnx.

4. ### AC6LAHam MemberQRZ Page

Assuming a 25 uH coil in the tuner, you can get a 2:1 SWR(50) with a load of 23-j400. If you want 1.2:1 the load jx has to be around -305. At around -j280 you can get an almost perfect match. Of course, that all assumes the tuner acts like a modeled tuner, big assumption.

If the coil Q is 100 a load of 23-j305 still loses ~32% of the input power.

Dan, AC6LA

5. ### BILLYBOB560QRZ Member

Simple L-network. From the 50-ohm end: shunt 46.15 ohm C followed by a series 837.9 ohm L to the Load.

Component values at 1.85 MHz: C = 1864 pF, L = 72.1 uH.

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Last edited: Oct 16, 2020
6. ### WA7ARKHam MemberQRZ Page

Goal is to fix the antenna so that it can be tuned with the existing tuner; not build a custom tuner...

I take your point that an L-network will always "work", even when a T-network wont.

7. ### BILLYBOB560QRZ Member

Then just add a series ~813 ohm (70 uH) L between the antenna and tuner. All the tuner then needs to do is transform 23 ohms to 50 ohms.

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Last edited: Oct 16, 2020