Touching, Brass Monkeys and a Versatile Singer/Songwriter

One of the things that caught my eye at this year's G-QRP Rishworth Mini-convention was a range of touch-sensitive paddles and associated keyers in the exhibition of homebrew. I'm afraid I don't know the brewer's name (but would be pleased to add my thanks here if anybody can help identify her/him).

I've got something of an affection for keys in general and have dabbled with making both straight keys and paddles (the latter just for fun) - but I've never tried electronic touch-sensitive paddles before. Having been touched by them (and vice versa) for the first time at Rishworth, I decided to make one...

I found a truly elegant design by Matthias Volkert, df4sq, in Sprat 48...

and - whilst I'm not interested in the keyer part of Matthias' beautiful, simple, efficient design (having the m0xpd PIC keyer and its Funky derivative), I decided to try the paddle section.

My version follows Matthias' words and music pretty closely, but with the addition of open collector outputs to connect to a keyer or a rig...

I knocked up a quick version on a solderless breadboard...

(eagle-eyed readers will see the power supply plug-in of a few weeks ago pressed into service)

The paddle was rough-hewn from PCB offcuts...

The whole thing worked very well indeed. I was keen to try it on air, but the bands were out of action last weekend due to a cacophany of QRM caused by something called CQ WW DX ("- . ... - / - . ... - / - . ... -" ad nauseam). [There is, of course, the possibility of shelter in the quiet haven of 30m during a storm of contesting - but that is occupied by my beacon!]

What's worse, I couldn't even go outside into the workshop to make a nicer paddle or a PCB for Matthias' circuit due to a spell of very cold weather! It would be nice to have been able to say "unseasonably cold weather" at that point - but extreme winters are becoming a habit.

Despite the frustrations of contesters, cold spells and failed attempts to build a switching bandpass filter, last weekend did have one high spot - and very high it was too...

A daughter had kindly given me tickets to see Sheffield's Versatile Singer/Songwriter in his "A Man with No More Rolls" tour at the DanceHouse...

Brilliant.

Anybody not familiar with Graham (a.k.a. John)'s work should take a look at his very acutely observed, skilfully delivered and immensely entertaining take on northern life.

...-.- de m0xpd

Multi-Band Beacon: WiP

I spent some time at the weekend looking at "upgrading" the Multi-Mode Beacon (Blogs passim) to MultiBand operation. The internal DDS makes all the frequency control easy - but I need additional BandPass filters to suppress unwanted sidebands...

I designed a set of filters, similar to the 30m version already in the beacon, based upon the series resonator design in EMRFD (page 6.76). Here's my Spice Model of the (three) filters, configured for 40, 30 and 20m operation...

The predicted frequency responses of the filters are shown in the graph below...

OK - so we've got a set of bandpass filters - how should we select between them?

Obviously mechanical switches are out of the question (the rest of the Beacon being electronically controlled) so I looked for a more subtle approach. I thought I'd found it in Doug DeMaw, w1fb's article in QST, January 1991, page 24...

... in which Doug describes switching between parallel filters using diodes.

I designed a circuit, in which the chosen band is loaded into a (74137) latching demultiplexer, which switches the biasing voltage to the appropriate diode switch - here's the important part of my design...

I even got as far as a PCB...

The system works, but only up to signal levels of ~ 100mV. Above this, the diodes introduce significant non-linearity (which negates the whole purpose of the bandpass filters!!). Unfortunately, there's around 0.3V of output from my present 30m bandpass filter in the beacon, so this circuit isn't suitable - back to the drawing board!

OK - I guess Doug only intended the design as a Rx front end band-changing scheme but I was expecting the switches to work up to a larger fraction of the diode forward voltage drop.

Today, in a recourse to good old brute force "steam hammer to crack a nut" engineering, I've ordered up a bunch of PCB relays. I'll replace those dumb, non-linear diode switches with something a little more clunky!

...-.- de m0xpd

Best East-ward dx

The last 24 hours have seen some pleasing dx spots of the WSPR emissions from my 30m multi-mode beacon (Blogs passim)...

As well as the familiar transatlantic hops, there is a nice spot from Steve, a45swl in Oman - 6049 km from my qth.



This is the furthest east my 6 Joule WSPR "flashes" have been spotted to date - and from the badly "out of tune" antenna system too.

Despite (what I imagine to be) the low density of receiving stations, it is nice to know that my signals are getting out to the Arabian Peninsula - thanks Steve.

...-.- de m0xpd

Breadboard PlugIn Modules

I am - as regular visitors will have noticed - a fan of "Solderless Breadboards", which I find very useful for prototyping. Their usefulness is much extended by the addition of simple "PlugIn Modules" - hardly a novel idea, but immensely practical.

Today I made a power supply module, to save me adding the same set of components almost every time I knock up a new circuit...

It implements a simple 5V supply, taking power either from a 2.1mm DC jack (e.g. from a WallWart) or from a 2-pin "Molex" header (e.g. from a Battery) and regulating with a 78L05...



In truth, I power stuff under development from bench PSUs (current limiting is such a good idea for the accident-prone) but I still find it simpler to have local voltage regulation on the board - saves messing around with knobs and voltage adjustments!

Notice the little LED to remind me when power is present.

Here's the finished board...



The power supply joins an increasing collection of such "PlugIn" modules I've made over the years - usually to interface a connector or switch to the breadboard without the use of flying leads (which always live up to their name and fly off in my experience).

Here's some of the family...



There's an FCC68 break-out (used to connect the Microchip ICD2 to a PIC project under development on the Breadboard - although I tend to use the PICKit 2 nowadays - not least because of simplicity in connection!) and two flavours of switch - one "upright" and one in a more laid back posture.

I'm going to add some more modules - perhaps my favourite QRP linear amp (as previously seen in the Radio Times amplifier) and some other RF building blocks.

...-.- de m0xpd

OT: National Treasure to Perform at The Wedding?

I would just like to add my own two pennies' worth to the groundswell of popular opinion expressing the hope that "England's Rose" will be invited to perform at The Wedding.

In light of the Chanteuse' last intrusion into Royal Soap Opera, this might present a (mercifully rare) opportunity to give another airing to that classic anthem "The Circle of Life".

...-.- de m0xpd

The Keys are Breeding

Spent an hour at Rochdale and District ARS' "Traditional Radio Rally" this morning. I'm not quite sure what is "traditional" about it - save the rather loose affiliation between some of the visitors and modern standards of personal hygiene.


Couldn't resist another "Key WT 8 Amp" to accompany the one I'd restored from Rishworth a few weeks back. This one is a No 3 Mk I, dated 1940 and carrying the further identifying mark "ZA4605" (on further inspection, I notice this is also stamped on the base of the Rishworth model)...

This MkI is differentiated from the key I got at the G-QRP Convention by the use of a compression spring under the arm (the Rishworth Key has a tension spring above) and by the solid, machined "saddles", rather than the diecast excuses which had failed on my earlier purchase. The flat faces and sharp corners of the machined components are visible on the new key...


If anything, the new key feels better than the one I restored the other week (in which there is a little play in the un-restored central pivot).

Also, I got an old instrument case (which will live again in a new application). I didn't buy it for the case but rather for the goodies I harvested from it...

It is worth the money I paid for EITHER the BNC sockets OR the switches - for both and the case itself, a bargain!

...-.- de m0xpd

To Tune or Not To Tune?

Now here's a pretty problem...

Last night inadvertently I left my multi-mode beacon (blogs passim) running into the g5rv - but with my MFJ 969 tuner in BYPASS Mode. The results were surprising - in fact, I think I have achieved significantly better dx than with the antenna "tuned".

Here's a map of spots over the past 24 hours...

The beacon is regularly spotted in North America, but this performance exceeds anything seen before - and the spot by Jay, w5olf in Colorado (not so far from my old home in WY) is the best dx (4537.4 miles) the beacon has achieved to date. This transatlantic spot and others into Florida and Maine were achieved this morning, continuing the recent trend for improved day-time dx. All this with the antenna de-tuned...

Here's the indicated SWR (as measured by sending a CW tone from the FT817 into the system - the beacon barely moves the needles of the meter) with the tuner active...

Here's the SWR with the tuner in BYPASS...

What's going on?

It appears that either i) there are losses in the tuner in "TUNED" mode that exceed the benefits of tuning or ii) the source impedance of the beacon is very different from 50 Ohms (the final stage is a low-pass filter, designed from standard methods assuming 50 Ohm operating impedance).

Perhaps you can suggest another explanation?

In the meantime, I guess I'll keep running the beacon into the UNTUNED g5rv !

...-.- de m0xpd