Autek

BATTERY INSTALLATION

Obtain a standard 9 volt ALKALINE battery. Battery life (6-12 hours with intermittent use) decreases drastically with a non- alkaline .Using your thumb, slide back the battery compartment on the back. Don’t pull it up and break it--it slides! Install the battery without pulling the battery leads excessively and replace the cover.Tap the on/off switch. The first number which flashes briefly is the program code version. A higher number may indicate a later date of manufacture.

The unit draws about 50 ma, rising to 80 ma. at 30 MHz. It has an “auto-off” feature to save the battery. The unit automatically shuts off after about 20 minutes on nonuse. To disable this feature: First turn the unit off. Then hold down the FREQ button. Then tap the on-off button ONCE, and release the FREQ button. You will not see the brief program code at turnon, confirming that auto-off is disabled.An AC adaptor , 9-12 V at 200-500 ma. may be used. Radio Shack #273-1552A and #273-1662 are suitable. Replace the battery when the display dims noticeably.

The screw near the coax connector is an alternate ground.

MODES

FREQUENCY

When you turn your unit on it enters the FREQ mode. The “tune” knob changes the frequency. The “fine” knob also changes frequency, but much slower.

BAND BUTTON

Tapping the band button changes to the next band. If you hold down the band button, the unit continuously cycles between bands.

FUNCTIONS

The measurement summary drawing on the next page summarizes the VA1 functions. Function 1 measures SWR, Rs and Xs. Function 2 measures Z, L and C, etc. When you turn the unit on it always starts in Function 1. To change functions, tap the Function switch until the desired function number appears. Then tap any other button (except on/off) to stay in that function. If you get confused about which function is selected, simply tap the function button ONCE to see the function, then tap any other button to stay in the function.

SPECIAL DISPLAY SYMBOLS

Each measurement mode has a special symbol on the left which further tells you what function you’re in. For example, SWR has a little box in the upper left, the C mode has a small c on the lower left, etc. Sometimes this symbol is written over if the number is too large, however. The sign of a number, if it is minus, is shown by a minus sign in the upper left. Xs, Xp, L and C can all be minus. No sign is shown for “+.“

If a number is too big, a large “H” appears on the right, meaning too HIGH to measure. This usually occurs when Z is larger than 1000 ohms, in which case all modes read high , except C reads “L.” But other conditions can cause this.

MODE CYCLING

Hold down the SWR and frequency buttons, and release them at the same time. Notice that the meter now cycles between the FREQ and SWR nodes. If you tap the buttons in VERY QUICK succession, cycling will also occur. By tapping all mode buttons very quickly you can even cycle through all 4 modes in each function. Cycling is very handy.

This mode displays SWR relative to 50 ohms, so that a 50 ohm resistor will read close to 1.00 SWR. The “H” appears for any SWR above about 20:1. This is the mode you use to find the resonant frequency of your antenna. Simply connect the transmitter end of the feedline to the RF5, select the SWR mode, and find the frequency of lowest SWR. Or measure at the antenna. See below for more details.

CHANGING LINE IMPEDANCE FROM 50 OHMS

You may be using 73 ohm line,or some other impedance, not 50 ohm line, and wish SWR to be referenced to this impedance.To do this: HOLD DOWN THE SWR BUTTON FOR ABOUT 1 SEC and release (in function 1.) The display reads “L 50” , showing that 50 ohm line is selected. Now tap the SWR button until you see “L 73” for 73 ohm line, or whatever line you want. To keep this, tap any other button, such as frequency. If you ever want to verify the setting, hold the SWR button down for 1 sec again, and release. Then tap any other button. Just as with the Function button, the LAST reading you see is used.

The unit always starts at 50 ohms on powerup. So you must change the reference at each powerup if desired.This impedance also affects the Rs ant and Xs ant calculations, discussed below, but has no effect on any others such as Rs or Xs.

Rs and Xs

Amazingly, any (linear) load can be completely described by its equivalent series resistance (Rs) and series reactance (Xs) at eacftfrequency. (See the drawings on Page 3.) This means that knowing As and Xs, the VA1 can calculate SWR. (See equations in the Appendix.)

IMPEDANCE (Z) and PHASE

Rs and Xs are are right angles to each other (see the triangle on page 3) . So they don’t add directly. Z is similar to DC resistance, in that it obeys ohms law. Instead of E= I A at DC, we use E=l Z at RE frequencies. But E and L are not necessarily in phase with each other, and the phase angle shows the difference. A phase angle of 0 degrees means the load is pure R with Xs=0, while + or - 90 degrees indicates a pure X, with R=0. Other angles indicate a mix of A and X.

L&C

The L and C functions convert Xs to its equivalent C and L value at the measurement frequency, which saves much calculation. Most L/C meters operate at some low frequency, such as 100 kHz or 10 kHz. The VA1 measures at the RF frequency of interest for a much more realistic value, especially for coils. For example, a toroid inductor has a totally different L value at RE because of core characteristics, and distributed capacitance changes the apparent L value of any inductor with frequency.

When measuring a lumped L or C it is important to keep Z between about 30 to 200 ohms for best accuracy. This is done by varying the frequency and watching Z. Also, lead lengths are very important, especially at the higher frequencies.