CW Test Key

That's what I'm calling it anyway. It's not really a CW key, and it's intended use is more so for testing through the generation of the CW carrier. What you will see in the picture, is a very simple device that plugs into the 3.5mm KEY socket on most CW capable transmitters (or the 1/4" socket with a converter). It consists of a simple IP65 button that can be used as a CW key and a toggle switch to have a constant CW carrier – great for testing.

You probably wouldn't use this for serious CW has the button action is pretty heavy so I'd imagine some RSI would result. However, for a quick test I think it'd be great.

It's real use though is for testing and tuning. That being, if I need to tune up my radio, rather than using AM I can send a nice and narrow low power CW signal and tune up. Or for testing, if I need an RF signal I can simply tune my radio to the frequency of interest and then flick the toggle switch for a continuous RF signal.

What led me to build this now, is that the 'DATA' port on my FT-817 seems to no longer be accepting 'Data In' – as in the audio. So although my digital interface can still trigger the PTT via the DATA port, the audio I send no longer seems to be received and thereby no SSB generated. (Testing on my digital interface seems to show it's working perfectly, and I can still transmit voice SSB with the FT-817.)

This is inconvenient as it happened while I was testing my 2200m transverter. You see, I was using fldigi to generate a tone via my digital interface into my FT-817 so that I could have an RF source to easily test with. But after stopping one test and going to start another, I noticed it no longer worked.

But now, with my little 'CW Test Key' I can easily generate an exact RF signal and I can do it without the need of a computer and digital interface. However, going forward I'm going to struggle to do things like WSPR and PSK31 on 2200m. I will need to modify my digital interface to use the Mic socket instead it seams. :/

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Convert Vpk-Vrms-dBV-dBu-mW-dBm

Owen Duffy (VK1OD) has produced yet another useful calculator on his website. This calculator makes it very easy indeed to evaluate power levels of your radio gear with your oscilloscope. Section 7 in 'Experimental Methods in RF Design' details measuring your power with a 'scope and provides the formulas you need. However, with this calculator you can make your measurements with your scope, and then just plug the numbers in and get your answer – couldn't be easier.

Enjoy! Thanks Owen!

Introduction to Transistor Biasing

I'm still working on developing a good understanding the use of transistors – and especially biasing for the application of amplification. As a result, I came across this great video on YouTube.

There are additional videos too – in theory a Lecture 12 that goes on to more biasing methods and their use as amplfiers. But I'm still to look and find that.

(Update: Full series can be found here: http://nptel.iitm.ac.in/video.php?subjectId=122106025)

2200m Transverter (G3XBM) Photos

Well, as promised here are the photos – sorry for the delay, had to head out for dinner. 😉

Reminder, this is for TX only – as I've got another setup for receiving. Now I'll need to move on to figuring out the antenna system – should be interesting. Hopefully soon I'll also do some traces and measurements with my 'scope to check the power output etc.

Photos:
1 – Close up of the completed 10MHz oscillator module – a basic Clapp Oscillator (I think) with a transistor buffer;
2 – Front view of the completed enclosure – currently I've still got to wire up that LED;
3 – Rear view of the completed enclosure;
4 – Inside view of completed transverter; and
5 – Another inside view.

In photos 4 and 5 you can see the modular design I went with. Start at top right (clockwise) we have:
1 – PA;
2 – Mixer and 137kHz buffer;
3 – 10MHz local oscillator;
4 – Input attenuator to reduce FT-817 signal from 500mW to 5mW for mixing; and
5 – Band pass filter for output.

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LF Transverter Oscillator Complete

Today I was able to complete the oscillator module for my LF transverter. As per the previous post, last night I completed the 10MHz oscillator, but today I added the buffer stage to it. Therefore, now I'd consider it a nice self contained module that I can hook into the mixer module once I build that.

I've attached a couple of quick iPhone photos for you and another 'scope capture. You can see I've built the module with lots of space on a single small prototype board (47 x 72mm) from Rockby Electronics. I'm hoping that I can build each of the individual modules on their own board and then link them together. Plus, spacing it out (rather than aiming for miniaturisation) will allow me to – hopefully – modify and/or fix it. Further, at the larger scale, doing them as individual modules will allow me to easily test each module but also allow me to improve modules in the future – if I see fit.

The oscilloscope capture is interesting. First, we can see the wave form has come closer to a sine wave as opposed to that in the previous post. This could be due to me using a 12V battery this time, but unfortunately I didn't have time to compare it with the 9V battery. Hopefully I'll get a chance to try with a 13.8V power supply soon – just need time to do so. Also, the change in wave is also due to the addition of the buffer – plus I was taking the reading from the output of the buffer (the wave is rougher at the output of the oscillator's transistor).

Also interesting in that capture is that I've included the FFT graph. This excited me greatly, as it gave me an opportunity at hands on to see the theory I'd learnt for my license upgrade in action. The FFT confirms the 10MHz signal (centred) but also shows the presence of the harmonics (2nd thru 7th).

One thing also interesting was that I noticed the buffer transistor was getting rather hot – the oscillator transistor did not heat up at all. Maybe this is because currently it's not linked to the other modules, or maybe it's because I'm using 2n2222 rather than the 2n3904 (which I was struggling to get, but now have some ordered). But, I'll guess I'll just have to see what happens – just another opportunity to learn.

Anyway, things definitely now seem to be progressing, so hopefully soon I can move on to building the mixer – maybe the week-end, we'll see.

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Work Begins on LF Transverter

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That’s right, tonight I started assembling my G3XBM transverter for 2200m. I’ve successfully got the 10MHz local oscillator going as confirmed with my latest toy – a basic Rigol DS1052E 2ch 50MHz Oscilloscope (cheap, but capable and all I need).

Seems it’s not quite the perfect sine wave I was hoping for, but hopefully it’ll do the job. The above image is taken from the ‘scope. Mind you, the design is for a 13.8V source, and I was just using a 9V battery – so perhaps the biasing for the transistor was a bit off. 🙂

Anyway, hopefully over the coming weeks I’ll work to completion. I’m building it in a nice modular fashion so that I can change parts as needed. Hopefully some photos soon. 😉