HTX-202 radios for foxhunting updated 5/8/2014 I currently have 9 usable radios, as well as 1 that's waiting on parts and another FOR parts. Somewhere I have one with a bad internal speaker. I recently swapped out 9 for jeff's since I don't need reliable tx. Reset Er1 by powering on holding Fn+D For making a beacon/fox There is 14mm of space between the front shield and the top of the transformers and capacitor in the 202 to fit a controller The mic/speaker connect to the front with the 3 pin plug Appears to use a 2.2k resistor to pull the mod pin toward ground to trigger PTT (2.2k for electret, probably 500 ohm works for condenser) The best injection point (for both audio and ptt) is at the mic jack. it's isolated from the internal mic via a cap, so it should be fine to leave it connected. Just dump signal in there at the jack, or on pin 1 of the mic board. Suggest running a #28 solid from pin 1 on the mic board around to the other side of the RF board and attach the arduino there. +5 is on pin 9 of the mic board and gnd on pin 5. Just twist those three together. rx signal level is probably on the orange or yellow coming from the top board (NOT the four wire connector nearer the squelch knob) confirmed, yellow is 2.4v no signal, down to 1.04v full scale, orange is squelch threshhold. (squelch is closed over 1v) there is no easy source of 1.0v for level comparison, will have to compare it against a fixed source. using #6 as a standard, 2 uV is needed to get full scale (S-9) 0.12 uV is needed to get a solid S-1 that's a pathetically low range S-9 can be cut to S-1 by adding in only 10dB of attenuation For VHF bands the recommendation defines S9 to be a receiver input power of -93 dBm. This is the equivalent of 5 microvolts in 50 ohms. The recommendation defines a difference of one S-unit corresponds to a difference of 6 decibels (dB), equivalent to a voltage ratio of two, or power ratio of four. ie S-9 is 50 uV each loss of one S-unit is 1/2 the voltage (or 1/4 the power) so S-1 would bed up at just under 0.2 uV looking for s-meter point in circuit SSPW on connector wire going to LCD driver to drive LCD bar graph SS/PW on connector wire 15 goes to IC301 pin 8 (comes into IC301 on pin 6 "SQL" ?) that comes from IC4 pin 11 (possible test point on other side of R35 a 270k?) which is the yellow wire going to one side of squelch knob (other side is gnd, center is orange wire, the source?) one of IC4's (MC3371DR2 2nd IF amp) functions is "meter drive" IC4 is on the bottom of the main RF board covered by the rear cover yellow is somewhat stable (not affected by squelch knob), orange is affected by squelch knob pin 6 on IF board: 2.55 v = min voltage (noise floor) 1.99v = s1 1.74v = s3 1.50v = s5 1.26v = s7 1.02v = s9 0.68v = max voltage (full scale) pin 8 of IC301 sends level to display (after inverting it?) is on the level board IC4 pins 11,12,14 14 is output to Q11 which handles squelching of the speaker and also outputs to the BUSY line (collector gnd on squelched) (14 and 15 get connected, 15 is ground) 12 is "squelch input" OK REFR pulses low for a few ms every 200ms or so, to "collect" a tx or rx reading from IC3, so IC3 APPEARS to not have any output when using a voltmeter, but it's there, it's just not easy to USE. Easier to just grab it off the squelch knob or pin 6 on the IF board. Though the dynamic range is only around 10dB, regardless of how you're displaying it. testing input signal directly into radio to see where the S meter points are at S-1 at -116 dBm S-3 at -113 dBm S-5 at -109 dBm S-7 at -106 dBm S-9 at -101 dBm Stand agrees, this is nowhere near the range you want the S-meter to have the low end is fine, the high end is way off https://en.wikipedia.org/wiki/S_meter S-1 is 0.2uV (-121 dBm / +34 dBm over 1uV) S-9 is 50.2 uV (-73 dBm / -14 dBm over 1uV) so S-1 to S-9 is +48 dBm on either dB scale therefore the meter going from S-1 to S-9 should represent +48 dB, but is only representing +15 dB dB + 107 = dB over 1 uV) R32 feeds the AGC into the op-amp for the meter, and is 39K - it needs to be increased, but this may cause the S1 reading to move in an undesired way at the same time R303 or R304 on Level board are probably what sets the scale, but will be a pain to change R304 is going to have to change also, the delta between S-1 and S-9 is just too small signal strength is how quickly A(+) can get its voltage above A(-) higher signal strength leads to lower A(-), meaning it takes A(+) less time to move up from ground to meet A(-) after REF is dropped