MATCHING BY CANCELLING Xs

All matching methods below can be used at the antenna (preferred) or at the transmitter end of the feedline, which is more convenient and could avoid adjusting a tuner for the antenna in question and have less toss than a tuner.

Fig, 9 shows an easy way to cancel Xs. Simply connect a component (L or C) with the opposite sign in series with the load. The component value can even be read by selecting the L or C mode.

For example, your antenna or other load measures:

Rs =35

Xs = +30

at F = 14.1 Mhz

L and C read:

So, if you add a 376 pf capacitor in series with the load, as in Fig. 9, the load will now look like 35 ohms, ideally, and SWR will be:

SWR = 50/35 = 1.42 for a 50 ohm line

Not bad, but you can do better with parallel matching, as shown in Fig. 10.

MATCHING BY CANCELLING Xp

Recall that the load also has an equivalent Rp and Xp which are not the same as Rs and Xs in general. As shown in Fig. 10, Xp is cancelled by connecting a component with the opposite sign in parallel with the load.

Continuing the example , you switch to Function 3 and read:

Rp =61

Xp=71

So you need to add a capacitor with X= -71 ohms at 14.1 MHz in parallel with the load. Unfortunately, the VA1 only converts series X (Xs)to a C value, so you have to do the calculation:

C = 1,000,000/(6.283 x 14.1 x 71)

So if you put the 159 pF capacitor in parallel with the load, you should have a pure R of 61 ohms.

This yields an SWR of 61/50 = 1.22 for 50 ohm line, which is lower than if a series capacitor were used.

Note: If Xp were negative, a parallel inductor (coil) would be needed for matching. The value of this coil would be

Since coils don’t usually have their their values labeled as capacitors do, it might be simpler to adjust taps on a coil and measure it with the VA1 until it has the desired X.

Examining equations A8 and A9 in the appendix you see that:

Xp is always greater than Xs, which means a smaller capacitor but a larger coil is needed. But more significantly,Rp is always greater than As. If you measure Rs less than 50 ohms (or whatever value you’re trying to achieve), then be sure to check Rp also, since it may have a more suitable value.

L= 0.34 (uH)

C=-376 (pF)

(= Xs)

(= -Xs)

VA1 Page 9