Quick and cheap dummy load for QRSS/QRP TX

In Belgium and don't have the rest of the homebrew shack with me but needed a dummy load and ability to measure the RF levels so knocked this one together.

I grabbed a tiny strip of veroboard and 20 1k 1/4 resistors, 15nF capacitor and a 1N5711 diode.

It is 2 sets of 10 x 1K resistors in parallel so 50 ohms. The diode and capacitor follow the dummy load so can use a cheap typical DVM to measure the RF voltage.

The 1N5711 limits the power to about 15W but the resistors would frankly pop well before then.

The circuit is not original, neither is the idea and I do not claim any ownership in any way.... I built the excellent NorCal SMT dumy load a while back.

The basic design can use larger wattage resistors but if you want to do this for something that might last a while then ideally you use identical resistors. This would mean 2 x 100, 4 x 200 etc... A cheap 10Wdummy load is 44 x 2K2 resistors.

Back at QTH I have 4 x 200ohm 25W chip resistors in TO220 packages bolted to a heatsink using insulated TO220 washers and a little heat sink paste. There are others that use these suspended in mineral or olive oil for QRO use (check out http://www.hanssummers.com/dummy.html) . I planned to bolt an old CPU fan to the heatsink to increase run time but mine never gets that hot.

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TNT Uncovered - Flea-Power (QRP) Telegraph Transmitter in the Pilot Radio's "Radio Design" magazine, 1930's

I found this article in the Lloyds Dipsy Dumpster - site, where you can find a lot of rare vintage radio articles, manuals and data sheets.

It is remarkable, that "Pilot Radio & Tube Corporation", well known as a manufacturer of the great Super-Wasp receivers, was a publisher of a Ham-Radio literature, handbooks and magazines, as well as many of early radio manufacturing companies. As for me, I like that sort of advertising much more, than modern spam in my mailbox and if it would be possible, it should be a nice choice to make this QRP transmitter using a native Pilot's parts only.

Anyway, when I've read this article, one interesting fact has drawn my attention - I can recognize the TNT when I see a TNT design, but in the text this transmitter has been described as a TPTG.. Moreover, there is a grid capacitor on the assembles view, but with a opposite description below: "condenser is not needed". So, in the article we can see that mysterious moment, when as the chrysalis becomes the butterfly, TPTG transmitter was transformed into a trendy TNT.

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More 80 Meter Vertical

Beth has commented that I need to get a "Frequent Buyer" card for my local big box hardware store. Since starting on this project I've been making trip after trip to buy yet one more bunch of screws, a particular clamp, a spool of wire, a ..... the list goes on. For a project that started with a $7 set of fiberglass poles this one certainly is a great example of "the devil's in the details".

I'm finally to the point of pruning it to frequency. Along the way I've fashioned a hinged base out of a large gate hinge and two conduit hangers, I've added 40 meter capability and I've made the bottom 24' a four wire vertical cage. Top loading is provided by two 6' elements forming the top ends of two of the guys, a coil wound out of 14 gauge insulated wire on a piece of 4" thin wall PVC sewer pile and a vertical 6' element. 40 meter coverage is provided by a 9' stub (connected directly to the top of the 24' vertical cage) that makes up the top of the third guy. Additional support is provided by tying the mast to my deck railing at approximately the 9' level.

Normally this will be a winter installation. I plan to paint the mast white.

Actual on the air reports will need to wait until I finish tuning it to 3560KHz.

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QRSS HB Build

Was sent this image of a QRSS homebrew build.
I then did a double take... it's from ET "Phone Home"

:-)

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QRPLABS QRSS kit

just melted solder on this

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Cable-TV Amplifier with 5 Outlets

Here's the design of a cable TV distribution amplifier (CATV). This cable TV distribution amplifier has 5 outlets. This amplifier boosts the TV cable signal with 18dB before the signal is split into 5. The design is based around a MAR-6 MMIC. This Integrated Circuit amplifies DC to 2GHz with about 18dB, uses only 15mA and costs around 4,5 Euro.

The CATV distribution amplifier circuit is built on a piece of double sided circuit board with one trace cut out with a sharp hobby knife. It is housed in a standard metal housing, that holds the 6 F-connectors for the HF. A 7805 is used to stabilise the electrical power.

The electrical power (8..30 VDC - 50mA) enters the housing via a (1n) feedthrough-Capacitor. A single diode protects the circuit from reverse polarity voltage. A 7805 soldered to the housing (GND) stabilises the voltage at 5 Volt. Two 100nF capacitors prevent the generation of spurious signals and noise by the 7805

The HF signal enters via a F-connector. An optional attenuator (0,75 - 20 dB) gives the ability to decrease the signal strength in case you should experience interference by intermodulation products. In my situation, I ended up adjusting the attenuator at the maximum level…

After the attenuator, the signal passes through a 1nF capacitor to block DC voltages and goes into the MAR-6. The input to the MAR-6 is indicated by a dot on the body and a chamfer to the input leg.

Power is supplied to the output of the MAR-6 through a 100 Ohm resistor and a 6 hole ferrite choke (1uH). DC current will be about 15mA (3,5 Volt DC at the output of the MAR-6). Another 1 nF capacitor blocks DC and only HF signal is sent to a passive resistor splitter, made from 51 ohm carbon film resistors. Input impedance is 50 Ohm for the MAR-6. Output impedance will be a little less than 75 Ohm. The splitter is build as a 'spider web' floating over the circuit board. Each output is has a female F-connector. All F-connectors are soldered directly to the housing.

After closing the lid of the housing, the circuit should be reasonably immune to the 5 x 1.5 kW Digitenne (DVB-T) transmitters built less than 3 kilometre from my house L

Safety ground
I placed the amplifier right where the cable enters our house, and routed coax to all outlets. The housing is connected to safety-ground with a copper wire.

CATV Amplifier Power supply
For power supply, I use a non stabilised adapter. Unloaded, the output is 8,5 Volt DC, just enough for the 7805 to do its job.

Source: Cable-TV distribution Ampplifier

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