Setup ARDFrx2-6.
Preliminary development data.
pa0nhc 20170926

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. Firts check for a short circuit.
- Connect a 2Adc meter in series with the + ploe of battery an + pole of the PCB.
- SHORTLY connect the battery minus with the minis of the PCB. 

The battery current is maximal 40mA. 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. 32mA Varies with gain setting.
FETs 1&4 operate.
IC1p8 +5.0V VR1 operates.
R24/C13 -B = -0.75 tot -0.79V D2 is OK.
R25/C11 +0.63V D1 is  PK.
R203 700mVtt / 1.25Vdc BFO operates. IMPORTANT :
if T1 does not osciilata, you HAVE to fix thi first.
R22/C32 ca. +2 tot +3V Detector operates.
REM: thsi volatge 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 to a receiver.
- Hold the small loop near the coil or circuit of interest.
- Tune the receiver to the frequency of interest.

4.    BFFO T1 (BeatFrequncyOscillator) 
Important :
If t1 does not oscillate, it has to be corrected first.

- Check BFO oscillation at 10.700 MHz.

REM:  a. If you want LSB reception, change C202 to 18 pF.
            b. If you only want to listen to pure AM, change crystal Xt to a frequency well outside 10.7MHz, for instance to 12.0 MHz, and change C207 for a trimmer.
                WITHOUT BFO signal, detector FET5, and the whole receiver is much less sensitive.
                The best value for C207 is when the sensitivity of FWT5 is maximal.

5.    Loacal oscillator IC1.
Set tune potentiometer R5 in position "Min frequency".
- Find the local oscillator frequency using a receiver.
- Adjust the core of T2 to 154.7 MHz.

- Set tune potentiometer to "Max. frequency".
- Check the oscillator frequency of IC. It should be around 156.55 MHz.

6.         Antenna coil L1.
- Feed the SMA input with a strong 144.4 MHz signal.
- Tune the ARDFrx2 to it.
- Adjust the core of L1 for max signal.

- Feed a very strong 10.701 MHz signal to the SMA input.
- Adjust L3 and L5 for max signal.

REM: with GAIN at max, you should hear the background noise of the receiver.
When feeding a weak 2m signal, a -120dBm 80% AM signal should be detect able.

8.        Gain adjustment.
By changing the value of R25, the max. gain can be adjusted.
By changing the value of R24, the min. gain can be adjusted.
The holes for these components in the PCB are made wider for easier component change. 

9        Protection of ears.
The maximal safe loudness is 85dBspl. And even at this level, long listening can be bad.
A to loud tick from on/of switching already 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 your ears and those of others using your receiver and headphone.

            How to :
- Connect the headphone always to be used together with thsi reciever.
- Tune to a strong carrier.
- Hold the microphone of a dB meter close to the membrane of the headphone.
- Adjust GAIN and TUNE for the strongest indication by the dB meter.
- Correct a to high loudness by enlarging the value of R20. At the same time decrease the value of C39.

REM : the combination R20 x C39 is part of the audio filter system . If R20 is changed to twice the original value, C39 has to be change to half its original value.

You also could corrct R20/C39 using the table below. Measure the new max. loudness afterwards.

Factory specification for the headphone 
(dBspl @ 1mW)
90 150 470
100 470 100
110 1k5 33
120 6k8 12

I do NOT take any resposability 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 loud noises are heard.