Another RFI mod of a speaker mic for DMR use

I bought a remote speaker-microphone (RSM) for a DMR portable from eBay (~$12 posted). Experience says that these suffer RF ingress which is seriously bad in DMR due to the amplitude modulation of the transmitted signal. This RSM had somewhat improved filtering around the electret compared to others I have purchased. Last update: 27th June, … Continue reading Another RFI mod of a speaker mic for DMR use

Another RFI mod of a speaker mic (41-80K) for DMR use

I bought a remote speaker-microphone (RSM) for a MD-390 DMR portable from 409shop.com, a 41-80K. They assured me it was compatible with the radio in digital mode, but it turned out to be lousy with ‘motorboat noise’ on tx audio due to RF ingress tot he electret capsule. Since the RSM was otherwise a good … Continue reading Another RFI mod of a speaker mic (41-80K) for DMR use

Another speaker mic modification to reduce RF interference

Remote speaker-microphones and DMR portables discussed RF ingress to Speaker Mics (RSM) used with DMR radios in digital mode. The problem I purchased a RSM branded Kenwood but obviously a Chinese fake for an MD-390 for about $5 posted, but it turned out to be lousy with RF interference in the form of the ‘motorboat … Continue reading Another speaker mic modification to reduce RF interference

Retevis MD-380 speaker mic modification to reduce RF interference

Remote speaker-microphones and DMR portables discussed RF ingress to Speaker Mics(RSM) used with DMR radios in digital mode. The problem I purchased a Retevis SM that was advertised as original equipment for the MD-380, but turned out to be lousy with RF interference in the form of the ‘motorboat noise’ on transmit audio. Dismantling the … Continue reading Retevis MD-380 speaker mic modification to reduce RF interference

NanoVNA – measuring Q of an inductor using s21 – fails?

There is a fashion of seeing s21 measurements as the answer to all things, and amongst the revelations is an explanation of measuring inductor Q using s21 shunt through configuration. Let’s explore the use of s21 shunt through to directly find the half power bandwidth of a series tuned circuit and calculate the Q from … Continue reading NanoVNA – measuring Q of an inductor using s21 – fails?

Review of inexpensive Chinese thermostat – DST1020

The DST1020 targets the market for inexpensive digital thermostats, the most popular being the STC1000. There are two novel features to the DST1020: uses DS1820B digital temperature sensor (well probably a Chinese clone); two line display shows PV and SV simultaneously. The DS1820B should be considerably more accurate and overcome the significant error in the … Continue reading Review of inexpensive Chinese thermostat – DST1020

Active monopole + RTL SDR + RPi Spyserver experiment

A brief experiment was conducted of a remote HF receiver using: 1m active monopole; RTL-2832U v3 SDR dongle; RPi 3B+ running Spyserver; and SdrSharp client. Above is the active whip antenna. Not optimal mounting, but as you can see from the clamps, a temporary mount but one that does not confuse results with feed line … Continue reading Active monopole + RTL SDR + RPi Spyserver experiment

nanoVNA – experts on improvised fixtures

A newbie wanting to measure a CB (27MHz) antenna with a UHF plug when his nanoVNA has an SMA connector sought advice of the collected experts on groups.io. One expert advised that 100mm wire clip leads would work just fine. Another expert expanded on that with When lengths approach 1/20 of a wavelength in free … Continue reading nanoVNA – experts on improvised fixtures