SOTA: F/MC-192 (La Ramière)

This was the final of three sites near Brive-la-Gaillarde that I had activated on a day trip starting near Bordeaux; the other two peaks were F/MC-263 and F/MC-178. What sets this site apart is that I was not only activating a summit, but a prehistoric megalith (I’m not aware if there is a program for that, but probably).

My first inclination was just to follow a road towards a commercial antenna site near the summit, but when I looked at the site on OpenTopo, I saw a point of interest within the activation zone, the Dolmen du Puy de la Ramière. The map also showed paths leading from roads to the dolmen. A quick check with GoogleStreet view showed me that there are signs along the street and a parking lot next to the trail head, so I decided to take the trail to the dolmen and pick an activation spot in the woods a bit off the trail.

OpenTop Map showing the SOTA summit (red marker) and to its right the Dolmen du Puy de la Ramière and related trails.
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FT817 Mike Mod à la M0UKD

I replaced the stock dynamic microphone element in my MH-31 microphone with an electret element, as described originally by M0UKD. As far as I can tell, it works at least as well as the original microphone.

The stock mike never impressed me, so I had the W4RT voice booster installed. I did not notice any improvement, but the mike picked up RF on occasion. Signal reports deteriorated over time and finally the microphone seemed to stop working altogether.

Front side of modified microphone board.
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5R8SV Satellite Ops

After I took the hexbeam down, sanded it, painted it and packed it away, I still had a G450 rotor on my hands, so I thought I would try my hand at satellite operation. Over last weekend, I literally lashed together a satellite station — the rotor platform is held to the roof with taut line hitches.

Our house isn’t ideally situated for satellite operation — particularly to the south where some tall pine trees blot out the sky, but in the other directions, the antenna can see down to about ten or fifteen degrees above the horizon.

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LED Audio Spectrum Display

 

An LED bar graph fabricated on a perf board. Some of the columns are lit up.This project came about, as usual, by accident. I was rooting through my box of IC’s for another project and came across a chip that I must have ordered sometime in the past and forgot about: the MSGEQ7, a “Seven Band Graphic Equalizer” chip. Not the best name — the chip doesn’t do any sort of equalization; it just analyzes an audio signal to generate information that can drive a display.

When I looked up the datasheet, it dawned on me that I had ordered the chip at one point with the intent of making something along the lines of a sound organ. Now that I had looked it up, though, I thought it would be more interesting to make bar-graph display that I could integrate into some future project.

This is a typical application for this chip and some quick web surfing turned up a few descriptions of arduino-based projects that put the chip to just such a use [1,2,3,4]. Between their descriptions and plenty of sample code, it didn’t seem like that big a task to roll my own.

So, let me describe what I did. The overall goal was to take an audio signal, feed it to the MSGEQ7 chip, and have it essentially break the signal into seven frequency bands, i.e., take the signal and display it very coarsely in frequency domain — sort of a poor man’s FFT.

Details are below, or skip right the demo video to see a working version of the display.

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suDDSon Receiver

Components strung together somwhat chaotically with wire on my bench
20 meter band pass filter, Sudden Receiver, VFO-in-a-box, HiPerMite audio filter, PC speakers.

My longish term goal is to build the LBS transceiver described by N6QW and KK6FUT (who I see is now AI6YR) and I am methodically working my way through that project.

However, I am not above taking a shortcut for instant gratification along the way. Remember the 80-meter Sudden Receiver variant I built a few weeks ago? Well, not much use for it in my current location. It occurred to me that I could gut the 80-meter parts of it and use the NE602/LM386 core as the rest of a very minimal direct conversion receiver for a more useful band, say 20-meters. So that’s what I did and long story short, it worked.

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Madagascar Mighty Mite Experiments

On one hand, it probably doesn’t make too much sense to try to refine the MMM (the construction of which was described in an earlier post): it’s more an oscillator demo than a building block of any more complex radio, but there are a couple variables that I thought would be fun to explore: choice of transistor, supply voltage and emitter resistor value. Tables and pretty x-y graphs follow.

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The MMMM Receiver

Prototype construction of the MMMM receiver. The, um, interesting position of the coils is explained below.

The 80m Madagascar Mighty Mite was suffering from “a tree falls in the forest but nobody hears it” syndrome. Eighty meters is a tall ask for Madagascar — there aren’t that many hams in the coverage area, and given local noise, I doubt any of them can hear well on 80m. It would be a long wait for a signal report about the on air performance of the MMM. Clearly, the thing to do was to create a mate for the MMM, the Madagascar Mighty Mite Mate (MMMM).

In keeping with the philosophy of back-to-basics rockbound simplicity, I decided to build an 80m version of the Sudden Receiver originally described by George Dobbs in SPRAT, and reprinted in 73 (October 1991, page 8, available online thanks to the Internet Archive).

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The Topper Amplifier Revisited

The amplifier built manhattan island style on a copper PCB I thought my 200mW Madagascar Mighty Mite (MMM) would benefit from some sort of afterburner, so I dusted off a project shelved in 2011: the Texas Topper amplifier. I had built based on a design by Chuck Carpenter and kitted by Rex Harper. I ran into a couple problems back then, including some difficulty getting the bias right on the mosfet at the heart of the amplifier. In another brilliant move, I managed to burn out said mosfet by grounding it while trying to get it and its heat sink to fit into a metal box.

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The Madagascar Mighty Mite

Finished mighty mite on copper board
The completed (yet unboxed) MMM.

Over the last few years, there have been a spate of postings from homebrewers taking inspiration from the Soldersmoke podcast to whip up various incarnations of the Michigan Mighty Mite, a very simple rock-bound QRPp transmitter. I’m a little late to the party, but here’s my story.

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