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.

QRSS HB Build

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

:-)

QRPLABS QRSS kit

just melted solder on this

Another K1 Build - this one will be mine this time.

Various shots going through the RF Part I build.

The Front panel and filter board already built.

The extensive home brew bench.

FtTuthill80 Build

Kits components as sent.

Following the pdf instructions of Dan Tayloe, N7VE

These are the build images from the kit I just started to build.
Up to the power test (used a 9V battery) and the blue LED lighting.

Blue LED

Diodes

Sorting the 0.1uF caps

0.1uF caps

More caps

And more

Electrolytics

Resistors

More resistors

More resistors

Applying 9V.

The LED lights blue.

Elecraft T1

Was recently given an Elecraft T1 auto tuner kit and as now working in Belgium thought I'd make it up. First started in hotel room.

.

The portable 'homebrew' bench is perfectly adequate. Note I have brought a 12" square of PCB to build on.

Initial components going in.

Relays fitted.

Fitted the underside capacitor.

Fitted the sockets and headers.

Built up the control interface.

First fitting. Looks good so far however, visual check of all the components against the build list and couldn't work out why had extra FT37-43 torroid. Then remembered there is an errata...

Oops... errata clearly state use 2 FT37-43 cores for T2 not 1.

No harm done, removed T2 and added the new T2 fitted easily.

Removed the PIC, added battery, checked the voltage through the 2N3906 when tune/pwr switch depressed and onto the regulator says 6V.

Added PIC and tested the power on, seems to be fine. Will test again once have working TX with me in Belgium.

dBm Meters using the AD8307 logarithic amplifier

I'm having a go at building a couple of dBm RF Power Meter from AD8307

The first is W7ZOI design having found a nice 500uA meter at w/e there is a nice construction website here. Also note W&ZOI own notes on callibration here. There are plenty of variations on this design and the daa sheet and application notes from Analogue Devces are worth a read. Some like this one use an AF amp to provide an audible feedback too

Part of the circuit from the design from N2PON (QST August 2008) uses temperature compensation. Basically he divides the pin 4 output of the AD8307 that is fed to a DVM through a resistor network containing a 10K pot that adjusts the GAIN to achive c1mV/dB with an NTC temperature compensating thermistor (c1K at 25'C) connected to ground so if there is any temperature changes the instrument retains a level of thermal callibration.

In many places this is not necessary but I know from experience my own shack does vary from -10'C in deep winter to +30'C in summer if it is unheated. Any meter is likely to be built into a die-cast box that will take a while to equilibrate too... so I am trying to use a thermistor salvaged from a PC motherboard (as had a few) with a 2k7 value at 25'C and c4K close to freezing and 500ohms when about 100'C (basically put it in boiling water and into ice water and measured). So I think could use it but would adjust the value of by placing resistors in parallel and series with to obtain 1K at 25'C.