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--- radios:dr-m06th [2026/01/08 17:34] – [Modifying an Alinco DR-M06TH 6m transciever for packet usage] g5rkt
+++ radios:dr-m06th [2026/02/13 23:17] (current) – [Modifying an Alinco DR-M06TH 6m transciever for packet usage] g5rkt
@@ Line 8: / Line 8: @@
 After tapping the discriminator & modulator the radio was bench tested using an 857D and a pair of NinoTNCs; it works on 4k8 IL2Pc beautifully. The main issue with testing was those Aerial Facilities dummy loads are **superb** at 50MHz!
-Ticking away happily as GB7WIN's 6m port! Live long and prosper little Alinco.
+Ticking away happily as GB7WIN's 6m port! Live long and prosper little Alinco!
+Mods:
+- Inputs for TX audio, pre/deemphasis and direct modulator inputs\\
+- Ouptuts for RX audio, pre and post filter\\
+- 6 pin mini-DIN connector on the rear\\
+- Selectable "1200/9600" audio output\\
+- 2nd IF filter replacement (6KHz -> 3KHz)\\
+- Second receiver SDR tap\\
 =====Schematic detail=====
@@ Line 41: / Line 50: @@
 Alinco had also left another dimple in the casting, presumably for a different model of radio, so I drilled that out and installed a mini toggle switch to allow changing between "flat" audio in and "filtered" audio in.
-=====IF Filters=====
-Since this radio is being used for narrow packet and not wide voice I elected to replace the IF filters in an attempt to tighten up the receiver, which is far wider than we need in our application.
-The first IF, FL2, consists of a pair of 10M15B 2-pole monolithic crystal filters. They have a reported -3dB bandwidth of +/-7.5KHz and 40dB rejection at +/-25KHz. The replacement parts are a pair of 10K6B 2-pole filters with a 3dB bandwidth of +/-3KHz and 40dB rejection at +/-10KHz.
-The second IF, FL1, consists of a Murata CFW455F, -6dB bandwidth +/-6KHz, -40dB rejection at +/-12.5KHz , which was replaced with a CFW455G -6dB bandwidth +/-4.5KHz, -40dB rejection at +/-10KHz.
 =====Other tweaks=====
@@ Line 65: / Line 68: @@
 The tap wires were routed around the front central case mounting post before soldering to reduce the chances of pulling a trace off the board. The eagle-eyed viewer will notice an extra wire in the area of the "flat audio in" wire - yes, I pulled off the orange wire's pad when adding the green wire. Silly billy. Nonetheless it was an easy fix :)
+=====Filter replacement=====
+The radio is set up to receive +-5KHz FM voice, but on packet we're using +-2.5KHz deviation. I replaced the second IF filter (CFW455F, -6dB BW +-6KHz, -40dB BW +-12.5KHz) with a tighter filter (CFW455H, -6dB BW +-3KHz, -40dB BW +-9KHz).
+=====SDR Tap=====
+To give us a bit more information about what is happening on site I opted to fit an SDR tap to the radio and feed it into an RTL-SDR Blog v4. Initial experiments show that with an S9 signal into the receiver and 45dB gain set on the RTL a -30dBm signal is reported by the SDR, and in full power transmit a -10dBm signal is reported; well within the maximum input power of the RTL dongle.
+The SDR tap board employed was the PATV type with no LPF as this board is being fed directly from the input LPF in the radio.
+{{:radios:dr-m06th:dr-m06th-sdrschematic.jpg?960|}}\\
+**Receiver front-end**
+Q1 is the input LNA and feeds a low-pass filter consisting of L4, L5 and L6. The hupRF board was tapped into the pole of L6 to provide a second receiver.
+{{:radios:dr-m06th-huptap.jpeg?nolink&960|}}\\
+**SDR Tap board installed**
+The whole thing just fits into the radio underneath the main PCB; liberal application of Kapton tape and some sticky foam on the underside of the case holds it in nicely. I opted to drill yet more holes in the casting to fit a rear SMA connector to prevent mechanical accidents :)
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-de G5RKT, April '25
+de G5RKT, Feb '26