VE7XEN's ham radio and electronics blog

Out of Band Power Control in the Motorola Radius M100 VHF

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I recently purchased a Motorola Radius M100 radio used on eBay, intending to use it for an APRS tracker or perhaps a digi. The radio arrived in perfect working order, making its 25W rated power across the rated band split (146-174MHz). It was a couple KHz low in frequency, but easily "warped" up to within a few Hz.

However I ran across some trouble when testing it with the local APRS frequency of 144.390MHz; the 25W rig was making nearly 45W and the software power control made no change at that frequency! After doing some research I found several articles detailing the issue with MaxTrac radios. Essentially the problem is that the power output of these radios is controlled by the microprocessor, which is given a series of tuning values during alignment that establish a power output control curve. However the tuning values only cover the band split the radio was built for, so when operating outside the normal band, the microprocessor just runs the power amp at full bore. Not healthy!

DIY 50Ω dummy load w/ peak detector

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dummy load

Having ordered a used mobile radio from eBay, I felt that I needed a dummy load for tuning and testing. While I was at it I figured I'd add a peak detector to get a reasonably accurate power measurement at the same time.

Quansheng TG-UV2 Update

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Last weekend I took the TG-UV2 out on a weekend road trip and exercised it a bit - periodic car to car traffic for 4 days. By and large it performed admirably, I didn't charge it all weekend and still had 2/3 indicated battery life upon returning home.

One problem I did encounter was transmitting on a hot day in the UHF band. For a while the transmitter was very finicky, when keyed with the PTT it would beep and display 'LOST' on the screen, not actually transmitting anything. The manual says "If PLL unlock, LCD displays LOST", so I surmise that when it's too warm the PLL's components drift and pull it off frequency. It's a bit weird that this only happens for transmit - RX was totally fine - but perhaps this transceiver uses dual PLLs to support split band/frequency RX/TX and for some reason the TX PLL is less stable with temperature or somehow gets loaded down by the TX stage. It's also worth nothing that VHF was totally fine during this period of failure on UHF.

Strange problem, I'm still quite happy with the radio but this was a tad frustrating while on the road.

Quansheng TG-UV2 Dual Band HT Review

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The Quansheng TG-UV2 is a fairly straightforward 5 watt, dual band 2m/70cm handheld radio of Chinese origin. It's a fairly direct competitor to the other popular Chinese radios like the Wouxun KG-UVD1. With a street price of approximately $85 USD shipped, it's one of the cheapest dual band handhelds available anywhere. The feature set is pretty complete, and for the price it's really tough to beat. Read on for my full impression of this HT.

Clock-Block Knock Off

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CBKO assembled image

A while back I spent some time building a stratum 1 NTP time server based on a Motorola Oncore UT+ GPS receiver and an old (decommissioned and free) PC Engines WRAP.1E-1 board. I was inspired by N8UR's (John Ackermann) essay on using the Soekris net4501 single-board computers as high-accuracy time servers, which I don't have - but I thought I'd do what I could with the WRAP. I rigged up a level converter and hooked the Oncore up to the WRAP's serial port, installed FreeBSD and got it up and running keeping good time.

Anyway, that's not what this post is about. I discovered quickly that the stability of the onboard oscillator really wasn't very good. There was a clear diurnal cycle, swinging about ±7.5μs according to ntpd. The solution here, I thought to myself, was to reimplement John's proven TAPR Clock-Block design (kits available from TAPR) with a couple of changes.

Passed the test! Basic+ earned!

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I finished my Basic qualification exam last weekend with a 95%, earning me access to all the Canadian ham bands. I've got a power limit of 250W DC transmitter input power and can't build my own transmitters, but I imagine that will keep me going for some time.

The test was pretty straightforward, all the questions are available ahead of time and Industry Canada even provides a practice test generation tool using those questions. Run through a dozen or so tests and you start to learn the correct answers, most of which are regarding regulations and operating procedures. Add a decent understanding of electronics to fill out the technical questions and it's pretty easy to get a good score and earn the additional honours privileges.

Thanks to Gary VE7AS for administering my test, and buying me breakfast!

Now christened as VE7XEN, I've decided to start this blog about my radio-related endeavours.