"Sweet as, Bro"

NZ 38 whisked me on to ZL-land where much has changed - Newmarket railway station has moved a few hundred metres, and they've even changed the name of my favourite local cafe.

Fortunately, they still serve up latte IN A BOWL...



I don't know if this is just an Auckland thing or a wider Kiwi thing - they certainly play up the Kiwi identity with that national icon a "silver fern leaf" in the froth...



After a couple of days in the office, I am now enjoying some R&R on the weekend in the Southern Hemisphere summer.

Today I took a trip on the ferry to Devonport...


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which is a really nice little "seaside town" offering an escape from the city environment in Auckland (not that Auckland is at all oppressive).

Looking back from the ferry gave a good view of the Auckland skyline, including the amazing Sky Tower...



Looking North-East, I could just make out Classique - the 22 meter cutter operated by Captain Mel - she is swinging from her mooring and only just visible in this snap from my iPhone (inside the red circle).



I sailed on Classique on an earlier trip to ZL in 2007...



Here's Classique at anchor in Man o' War Bay off Waiheke, where we spent the night...



Back to today's visit...

I walked along to North Head



where there are the remains of some old gun emplacements, protecting Auckland harbour from invasion. Nowadays the guns are rusty relics and the headland gives good views over to Rangitoto (the volcanic island that dominates the harbour)...



and back towards Auckland...



I finished the trip with a walk up to the Devonport Naval Base and visited the Navy Museum which was worth the walk - especially as entry is free!

After the ferry trip back to Auckland and some snooping around the NZ America's Cup boats, I strolled back to the curiously named "Britomart" public transport hub...



to catch the train back to Newmarket and my Hotel - great day!

...-.- de m0xpd

Hua Qiang Bei Lu Technology Market

Took the train from Kowloon up to Lo Wu and entered BY-land at Shenzhen on Sunday 31st Jan. The border is pretty civilized on a Sunday – last time I was there it was Monday morning and was a heaving, hurrying mass of humanity.

Highlight of the visit to BY was a trip to the Hua Qiang Bei Lu technology market – a vast area of retail and wholesale electronics outlets.

I was walking around with my eyes and mouth wide open – just like my first visit to Hamley’s, the London Toy store, forty-something years back. Think Dayton and Friedrichshafen rolled into one and you get some idea of one corner of this place. It even extends over multi-storey buildings…



Inside there is everything from family-run stalls selling components to organisations who will manufacture a product to your design in drops of 100k units.

I turned down the 5W dual-band handie for less than £50 (the fist is mightier than the voice) but fell for some high voltage electrolytic capacitors for my valve games (blogs passim) from these people…



and some LCD displays for the frequency counter circuit I use. Oh yes – I also couldn’t resist those 78L05s for tuppence a throw!

Here’s some of the haul from a short afternoon stroll around the market ...



Next time I go (April) I’ll be taking a bigger suitcase!

This trip, which has reached proportions of almost a “world tour”, continues with a flight to ZL on Wednesday 3rd – watch this space!

…-.- de m0xpd

vr2/m0xpd meets Häagen Dazs

So – now for a little travelogue…

Arrived in Hong Kong on the afternoon of Saturday 30th Jan, after the usual exhausting flight (made better by great service from the Air New Zealand crew) and transferred to the Harbor Plaza Metropolis Hotel in Kowloon.

During the transfer I noticed for the first time the number of container ports in and around Hong Kong – add them together and you get an operation big enough to make Felixstowe look pathetic!

I checked into an upgraded suite, which gave me the real benefit of access to a cocktail bar happy hour (which, mercifully, lasted longer than an hour) with great views over the harbour towards HK…



…and the dubious benefit of Häagen Dazs theming – which is easy enough hanging on the wall above the bed…



… but impossibly distracting as a frame for the TV…



Unfortunately, the fridge was empty too!!!

Next on the itinerary is China.

…-.- de m0xpd

Wobbulator

Well, after all the fun and games with the IFTs you may remember I finally built a Wobbulator.

The "glitch" in the first response captured with the device was traced to a flyback issue (the point where the voltage controlled oscillator flies back from the top of its sweep to start over at low frequency again).

Here's a decent response of one of my experimental IFTs in close-to-critically coupled tuning, made with the Wobbulator...



Having gone to the trouble of brewing up the Wobbulator and finding it useful, I decided that I would put it in a box for longevity and ease of use...



The front controls...





... give me manual frequency selection (via the knob), manual / swept frequency (switch at lower left) and low / high impedance output (switch at centre). Speaking of high impedance, it is so high that the shunting capacitance of a 1meter coax connector becomes very significant in measurement - I'm learning all the time in this strange, high impedance world!

Having enjoyed more success with the experimental IFT homebrewed with axial RF coils than with home-wound coils on sewing machine bobbin formers (described here , I made a second "axial IFT"...



... and popped it into the valve superhet project (blogs passim).

The result is pretty convincing - best performance so far (although still with too little overall gain - working better into headphones than speakers). I could use the Wobbulator to measure an IF response in situ (this is important, given the effects of stray capacitances etc mentioned earlier)...



Must dash now - got a bout of business travel to attend to!

To tell you the truth, I made this post from the Thai Airways Royal Orchid Lounge in Hong Kong Airport during the business trip - but that's another story. Come to think of it, Bill Meara has a "travelogue" section on Soldersmoke, so perhaps I'll post some travelogue too!

...-.- de m0xpd

Capacity Housing Crisis

Here’s a sad little story for you…

I can’t say why it is but – ever since I started dabbling with electronics at the age of 10-ish – I have always accommodated resistors in more luxury than their passive cousins the capacitors.

I can’t say why but there are a few obvious factors…
1) I used to have more resistors than capacitors so housing the large number was more pressing than housing the few
2) when I was young I could figure out the colour code and so identify resistance values but found the mysteries of capacitor labelling more confusing. A resistor of known value is easier to place into pigeon holes with others of nearby value, whereas an unknown capacitor is harder to place.
3) Colour-code aside, I had the ability to measure resistance with a simple multi-meter – but had no capacitance meter (indeed, I still don’t). All the excuses about housing the named and known before the unknown above apply again.
4) To my simple mind, a resistor was always a resistor – whereas capacitors differed not only by value, but also by type. How could I manage all these ceramics, electrolytics, tantalums, polyesters, not to mention all those unidentified components with no measurable resistance which just HAD to be capacitors?
5) I can’t think of the fifth excuse – let’s just say…

The consequence of all the excuses above is that capacitors were always a jumbled, homeless mess, whilst resistors lived in luxury.

Fairly early on in my hobby “career” I got some sets of drawers which allowed me to separate the decades into a sort of “E3” series. Now I use a slightly expanded “E6” series of drawers with internal dividers to give me a unique place for all the E12 values from 10 Ohms to 1 MOhm.

One of the troubles with getting into radio homebrewing rather than the mix of AF and digital I played with before is that capacitors (and even inductors) take on a much more important role. It became such a trouble that it actually reached that threshold which triggered me into action the other weekend…

I decided to start a housing project for the ceramics! It doesn’t solve all the housing crisis for reactive passive components at m0xpd but at least it is a start.

Here’s what I was struggling with …

A stock of ceramics on bandoliers,



which became tangled up whenever you took your eyes off them, were difficult to find and involved the frustration of edge cutters or tearing (often leaving glue deposits on the wires, making them difficult or smelly to solder) before use.

A similar stock of ceramics in zip bags,



which were difficult to sort through and difficult to open / close.

Plus - if I’m honest - I even had a big zip bag with a lot of ceramics I’d used once in a circuit and then removed – I was too lazy to find the right bag, so they all ended up in the big “pot luck” bag.

It was taking too long to find the right capacitor and the “pot luck” bag was getting too big, so something cracked in side and I stopped off at the Stockport branch of Maplins and made the rash purchase of two Component Storage Boxes (order code: AN38) at the reasonable price of £1:99 a piece.

These have three rows of six compartments each row – giving me space for all E6 capacitor values in each decade – one box covers the pico’s and one the nano’s. I even went so far as labelling the whole collection…



It is an improvement – but I can see a couple of issues emerging already:
1) I’m going to have to buy some more stock to fill those unsightly empty compartments
2) I’ll swear impressively when I drop a box with the lid open.

I guess this is a small price to pay HI HI

…-.- de m0xpd

More to this than meets the eye...

This weekend I took another look at the IFTs - you may remember I had made one to the new, improved, "taller" design and needed a second. Well, here it is, installed in the Valve Superhet project - now featuring due espressi



Good news - where before I could copy CW on headphones, now I could copy voice in speakers! That's real progress, I guess - but there are limits to how many aviation meteorology reports or Radio Taiwan shows a boy can stomach.

However, I still had a much higher loss to contend with than the writings of other enthusiasts suggest I should expect (I have no "real" IFT to compare against). So, I spent some time chasing down the origins of this disappointing performance. My (interim) conclusion inspired the title of this blog; "there's more to this than meets the eye".

A little reading around the web led me to invest some time in reading more of Max K4ODS's website "Fun with Tubes", amongst which is an interesting idea for IFTs made with axial chokes . The thing that rang the bell with me was the fact that I'd already messed with axial chokes along the way to building the present IFTs, as described here .

I quickly made up an IFT using the "chassis" of one of my original devices, replacing the coils wound on sewing machine bobbins with 1mH axial chokes, as you can see here...



I had already been amazed when playing with the IFTs with the very low levels of coupling between the coils required to get the characteristic "critical" response. The (relatively) small coupling between the two coils in the photo above is about right for critical coupling - amazing!

I built the "axial" IFT more with a mind for experimentation than use and - in playing around with it - I stumbled on another key realisation (for me at least) ... there is CAPACITIVE coupling between the primary and secondary circuits of my IFTs which is almost as significant as the (intended) inductive coupling. This prompted a lot more messing with Spice models but - rather more practically - I decided it was time to re-visit an idea I toyed with on an earlier blog - I would build a Wobbulator.

Don't know what a Wobbulator is? Wikipedia does !

Here's a pic of the quickly knocked together m0xpd Wobbulator



The ugly board (left) includes both the voltage-controlled oscillator and a first try at the sawtooth "timebase" circuit. The circuit on Veroboard is an improved timebase circuit.

Here's the first result from the Wobbulator...



I don't yet know what the peak at the left (low frequency) end of the trace is - I haven't had a chance to get used to it / de-bug. However, you can see the near-critical response of the IFT made of axial chokes (seen earlier in this blog).

Now, armed with a wobbulator, I hope to be able to conduct some more orderly "experiments" with my H/B IFTs and with the Superhet project as a whole. Watch this space!

...-.- de m0xpd

New IFT

Long time no blog...

I've been doing Christmas, the Children's Birthdays (all three of which fall in the first week of January), bad weather, computer problems, work etc.. That's my excuse anyway!

The beloved got me a "Made From Junk" 969 Tuner for Christmas (which shall be the subject of a future blog). It works but - let's just say - it lives up to its name! More of that later. For the moment we return to the Valve Rx project (Blogs passim).

I ordered up an ECH81 over the holiday season to replace the ECH84 I'd been using. The new tube only cost me £4.85 from The Tube Shop so the wallet didn't take too much of a bruising!. For reference, the pin-out of the ECH81 is shown below...



The new mixer valve didn't really change much - the receiver works but only just! As I knew that all the stages worked OK, I turned my attention to the great unknown in the project - the Intermediate Frequency Transformers.

The whole project started with an idea to learn something about valve superhets, within which the IFTs are obviously an important part. I'd made some simple units (described here) , which displayed pretty disappointing Q-factor, so I modified to the ferrite-cored version described here. You can see the last two generations of (attempted) IFTs here...



I decided to look again at the whole theory behind the IFT and soon realized that I'd neglected to control the single most important variable in my prototype devices; the coupling. My IFTs (like most others) have two resonant sections (think of them as the primary and secondary of the transformer). The response of the whole system is critically controlled by the degree of coupling between these two LC resonators.

I was inspired by to make a Spice model of the IFT by Max K4ODS's work, reported here .

Here's my Spice schematic, shown with a high degree of coupling (k=0.1) between the coils of the IFT...



My Spice model showed me that - with high coupling - the "IFT" can give two quite distinct peaks (associated with the two modes of the system)...



Looking again at my second-generation IFT, I realized that this was exactly what I was seeing - I had much too high coupling (I'd managed this as an accidental by-product of the desperate bid to increase the Q of each LC section). So - I needed to build another IFT with variable coupling between the two stages - simply achieved by varying the spacing between the two coils.

I couldn't vary the spacing of the coils in the existing devices (pictured above) as there wasn't too much space available and (more importantly) I'd stuck everything fast with glue!

I quickly made a new IFT, using the same design as before (I had previously etched a batch of the "end plate" PCBs) but with...
1) more "height" (so I've got plenty of space to slide the coils relative to one another - whilst keeping clear of the end "plates")
2) coils on Ferrite formers sliding on a central dowel



Now, I could tune each section to 455 kHz (by driving the other section directly from a 50 Ohm RF generator output) and observing the response on the 'scope, THEN make the crucial adjustment of coupling to the near-critical value. Sure enough, I get the shape predicted by my Spice model (except for losses - which I shall try to understand in more detail later)...



The tuning of the IFT changes as it is mounted in its shield can (made here out of an Illy coffee tin - I've moaned before about the difficulty of getting tins without corrugations, so I've left the brand name clearly visible in thanks to Illy)...



Now we have something that actually behaves the way it should, I couldn't wait to try it in the receiver...



The good news - it really has made a difference - I can clearly copy CW in the contest currently running on 80m (albeit in headphones). I hope that, when the other "IFT" is replaced with something more worthy, the whole receiver will come to life.

That, I'm afraid, will have to wait 'til next weekend.

...-.- de m0xpd