Differences

This shows you the differences between two versions of the page.

--- radios:dr-m06th [2026/01/08 17:34] – [IF Filters] g5rkt
+++ radios:dr-m06th [2026/08/07 20:58] (current) – Mort upgrade: tighten emphasis markers so they parse again 0.0.0.0
@@ 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 -> +-4KHz or +-3KHz)\\
+- Second receiver SDR tap\\
 =====Schematic detail=====
@@ Line 49: / Line 58: @@
 {{:radios:dr-m06th:dr-m06th-pamodule.jpg?nolink&960|}}\\
-** Detail of PA module **
+**Detail of PA module**
 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.
@@ Line 59: / 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 (CFW455G, -6dB BW +-4.5KHz, -40dB BW +-10KHz). Based on the radio's S meter it's made a vast improvement, and decodes from BDH and RDG are solid! I have an even tighter one which I may chuck in down the road (CFW455H, -6dB BW +-3KHz, -40dB BW +-9KHz), perhaps.
+=====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 :)
 ----
-de G5RKT, April '25
+de G5RKT, Feb '26