Setup ARDFrx2-6.
pa0nhc 20171129

IMPORTANT : the negative pole of the 9V battery is INSULATED from the mass plaines !
Be careful when measuring. If a short circuit happens between +B and a mass plane, D2 immediately is damaged.
D2 then has to be exchanged.

Checking and adjusting.

1. First check for a short circuit :
- Connect a 2Adc meter in series with the + plus pole of the battery and the plus pole of the PCB.
- SHORTLY connect the battery minus with the minis of the PCB. 

The battery current is maximal 30mA. If 150-200mA runs, the "+5" is shorted.

2. After that, check the following items, using a hiZ meter and a calibrated >= 20MHz oscilloscope.

I (B+) ca. 17 to ca. 32 mA Varies with gain setting.
FETs 1&4 operate.
IC1p8 + 5.0V VR1 operates.
R24/C13 - B = -0.75 to -0.79 V D2 is OK.
R25/C11 + 0.63 V D1 is  OK.
Gain pot "min" - 0.43 Vdc R24 (22k) sets min. sensitivity
Gain pot "Max" + 0.094 Vdc R25 (47k) sets max. sensitivity
R203 700 mVtt & 1.25 Vdc BFO operates. IMPORTANT :
if T1 does not osciilata, you HAVE to fix this first.
R22/C32 ca. +2 tot +3V Detector operates.
REM: this voltage is dependent of the signal strength 
injected by BFO T1, also of the value of C207.

1/2 B+ 
= +3.0 to +4.4Vdc
& max. audio is 3Vpp.

IC2 operates.

3. Connect a coax cable with a small loop at the end to a receiver.
- Hold the loop near the coil or circuit of interest.
- Tune the receiver to the frequency of interest.

4.    BFO T1 (Beat Frequency Oscillator) 
Important :
If t1 does not oscillate, it has to be corrected first.

- Check BFO oscillation at 10.700 MHz +- 1 kHz.
           WITHOUT BFO signal, detector FET5, and the whole receiver is much less sensitive.
           The best value for C207 is when the sensitivity of FET5 is maximal for very weak signals.

5.        IF coils. 
WARNING : use a precise fitting trim key and do not press to hard !
- Turn the gain pot to max gain.
- Adjust L3 and L5 repeatedly for max noise. 

If a core is fully to the bottom, thea add a small capacitor of 3p3 to C25 and/or C26.
If a core is fully on top, than change the value of capacitor C25 and/or C26 to a bit lower value.

6.    Local oscillator in IC1.
WARNING : for L2 and L1 use a special well fitting trim key 1mm x 2mm !! See partslist.
Set tune potentiometer R5 in position "Min frequency".
- Find the local oscillator frequency using a receiver.
- Adjust the core of T2 to 133.3 MHz.

- Set tune potentiometer to "Max. frequency".
- Check the oscillator frequency of IC. It should be around 132.45 MHz.

7.         Antenna coil L1.
- Connect a 50 Ohms antenna. 
- Tune the ARDF receiver to abt.144.7 MHz
- Adjust the core of L1 for max. antenna noise or signal.

        Sensitivity :
a. When feeding a weak 2m signal, a -120dBm 80% AM signal should clearly be detect able.
b. Disconnect the antenna
c. Connect a 50 Ohms dummy load. The background noise should drop a little in strength.
d. Disconnect the dummy load, and connect a 50 Ohms antenna.
    In city environment the background noise level should rise notice able.

8.        Gain adjustment.
The holes for these components in the PCB are made wider for easier component change. 
With a dummyload connected to the antenna bus, and correctly adjusted max. gain, the audio noise voltage measured at R19 should be abt. 0.3 Vac.
By lowering the value of R25, the the sensitivity with Gain pot set at "Maximal" can be enhanced.
- By lowering the value of R24, the sensitivity with Gain pot set at "Minimal" can be reduced.

9        Protection of every ones ears (Fb6 / FB7).
Listening for a long period to a sound pressure of 90 dB will cause damage to the ears.
Even ONE very loud "tick" caused by on/of switching also can cause damage.
If someone experiences ear-sizzling or whistling, a few days rest is advised to try to minimize possible damage. 

YOU are responsible for to preventing damage to ears of everyone using your equipment. 

The best way to reduce the acoustic output of the headphone, is to insert series resistors between the PCB two "HP" connections and the headphone two chassisbus connections. See schematic. 
REM : The left and right channels of the headphone bus should first be connected in parallel.
            Headphones can differ widely in audio output. You have to measure sound pressure to be sure (see photo).

a. Connect the headphone which from now on will be used together with this receiver.
b. Tune to a modulated, strong AM or SSB signal.
c. Set a dB meter to dBa and slow reading.
d. Hold the microphone of this dB meter close to a membrane of the to be used headphone   ==>>
e. Find the spot of maximal loudness.
f. Adjust the receivers GAIN and TUNE for the strongest indication by the dB meter.
g. Note the dB meter reading, and calculate the needed attenuation for maximal 85 dBa reading.
h. After modification, check maximal loudness again.

I do NOT take any responsibility for all those actions.
YOU are responsible for your ears and those of others using your receiver and headphone.
Be aware of possible UNRECOVERABLE damage to ears when (short or long term) loud noises are produced.