Differences

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--- radios:dr-m06th [2026/01/06 02:31] – m0mzf
+++ radios:dr-m06th [2026/02/13 23:17] (current) – [Modifying an Alinco DR-M06TH 6m transciever for packet usage] g5rkt
@@ Line 6: / Line 6: @@
 The PA puts out ~20W and can be adjusted using VR1. The deviation is adjusted with VR2 and is set ~5KHz from the factory. On receive it's (apparently) very selective & sensitive, and the second IF filter is 20KHz wide so this TRX might even work on wider bandwidth modes. Using an IC-705 as a reference receiver the wideband PLL phase noise looks to be very low and there are no horrendous key-up transients a-la FT-1500M.
-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!
+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!
-I also replaced the IF crystal filters with tighter versions to help knock out the sproggies adjacent to our channel.
+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\\
-Ready to go as GB7WIN's 6m port! Live long and prosper little Alinco.
 =====Schematic detail=====
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 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 classic 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 59: / Line 60: @@
 ** Detail of PA module **
-Horrifyingly there was no thermal paste anywhere in the radio! I suppose they had a dry day at the Alinco factory. By its condition this radio has barely been used, if at all, so hopefully no harm has been done - I liberally applied that horrid white Servisol thermal transfer paste to the PA and linear regulators. After holding the radio in transmit for a few minutes at full power the heatsink becomes appreciably warm, but not remotely hot - and the PA module is the same temperature so good thermal contact was achieved. After dialling back the RF power from 22W to 10W and leaving it in transmit for 10 minutes the heatsink had reached equilibrium and was ~40C with no forced airflow. At 10W the radio drew 1.6A at 12.2V, so that's ~10W thermal into the heatsink which it certainly appears appropriately sized for.
+These radios (I've got two) don't have any thermal compound between the PA and heatsink so I liberally applied that horrid white Servisol paste to the PA and linear regulators. After holding the radio in transmit for a few minutes at full power the heatsink becomes appreciably warm, but not remotely hot - and the PA module is the same temperature so good thermal contact was achieved. After dialling back the RF power from 22W to 10W and leaving it in transmit for 10 minutes the heatsink had reached equilibrium and was ~40C with no forced airflow. At 10W the radio drew 1.6A at 12.2V, so that's ~10W thermal into the heatsink which it certainly appears appropriately sized for.
 =====Finished article=====
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 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 :)
-=====Test data=====
+=====Filter replacement=====
-None yet. When I get access to my DSO and find someone with a specan I'll post the results up here.
+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 M0MZF, April '25
+de G5RKT, Feb '26