Invertor frequency adjustment

[Dave Liquorice]

Does anyone know if the "mains" frequency of the cheap 300W or so invertors you can get is easy to tweak?

Being slightly involved in the local Brownie/Guides/Scouts Thinking Day on the Air activities this weekend I looked at what my amateur radio licence will let me do and find that I now have a "full" one.

Being in the middle of no where and surrounded by high moors I've never bothered seeing if there was any VHF/UHF activity but now I find I can use HF... I could be tempted to dust of the trusty Creed

444 teleprinter but that has a synchronous motor designed to run the machine at 50 baud from 50Hz mains.

RTTY operation on HF uses 45.5 baud, so I was thinking that a cheap invertor with the frequency tweaked down to 45.5Hz would get the machine onto HF at the right speed. Easier and cheaper than getting a suitable gear set made up and simpler to change machine speed as well.

The only other snag I can possibly see is the motor objecting, maybe over heating? Is that likely? Motor rating probably about 50W. I'd also make sure I got an invertor with a decent waveform not a square wave, which I'm sure the motor would object to.

[Harry Bloomfield]

Dave Liquorice formulated on Saturday :

Why mess about with an heavy power hungry Creed, when you can do it all in software with a light and portable laptop?

[Terry Casey]

Would it be easier to knock up an interface which reads in the data at 50 baud and reads it out at 45.5 baud and vice-versa?

You might need a small buffer for transmit but, unless you've got a touch typist (or you are using a punched paper tape) I'd expect there to be plenty of gaps between characters for your device to catch up - and you only need a tenth of a second between them!

You would then be able to use the Creed on any mains supply, whether battery derived or not. What happens 'on the day' when your modified invertor packs up and you're offered a replacement by another parent/helper?

[Huge]

Throw the Creed away and buy this;

you can do packet, AMTOR, SITOR, CW and ghod knows what else (it's been so long since I used mine that I can't remember what it can do - assuming it still works.)

[Ian Jackson]

Or

[Huge]

how long it is since I did any amateur radio (~20 years). Indeed, I don't even know what the licensing situation is (still Class A/Class B and Morse tests the last time I was active). I briefly subscribed to uk.radio.amateur over Christmas, but it's the same cesspit it always was.

73 de G0CNR.

[Terry Casey]

Perhaps he wants to demonstrate the old fashioned methods to the "local Brownie/Guides/Scouts" as part of their "Thinking Day"?

However, he says that it is "this weekend" so, even if he meant next weekend, he still hasn't got much time to do something about it!

Going back to the original question, it will depend on the circuitry in the invertor how easy it will be. If it has a free running oscillator, it shouldn't be a problem but, if it is derived from a crystal, finding a replacement ain't gonna be easy ...

[Andrew Gabriel]

When you reduce supply frequency to an induction motor, you should reduce the voltage by the same amount. However, 10% may be within the motor's margin, particularly if it's operating below max temp. The torque falls off quickly though. Tends to be OK for something like a fan where the load's torque also rapids drops at lower speed, but you need to be sure there's enough torque to get the motor starting in the first place.

[Dave Liquorice]

Because I can. B-) Using a computer for RTTY is cheating IMHO. Now for a mode that you can't and never was done mechnically it's a differnt story. I have a TNC card for packet radio somewhere, not sure I have a PC with and ISA slot though. My Creed doesn't have that sort of problem...

There is also an element of showing how things were done, The Creed also has tape punch and reader, so at a demo people could take away their name in a pattern of dots, both in baudot and spelt out. B-)

[Dave Liquorice]

To late for this years event which is today and tommorow. Maybe next year... Though having looked to see what my G6 licenece will let me do I might get myself back on the air but having looked at the price of HF rigs these days it's not a cheap hobby anymore! Even 20 - 30 year old sets on eBay are a few hundred quid.

I expect Quartzlab still exist, get one made. B-) I very much doubt that a cheap inverter would be crystal based though.

[Dave Liquorice]

This is most definitely a big synchronous motor not an induction one.

As I understand it induction motors need to slip (asynchronous) to produce torque where as synchronous one produces torque without slip (within limits...).

It is vital that the speed of rotation of this motor is accurate otherwise the timing of the generated signals is incorrect or the timing of the position checking of the magnet will be wrong. Either case producing garbage.

[Tabby]

Indeed.

Tweaking oscillators shouldnt be too hard, xtals included, ceramic resonators maybe not included. On-chip ones I dont know any way to tweak though.

Voltage adjustment is easily taken care of with a series capacitor if you can calculate it correctly. DONT play with series caps without calculating, bad news tends to result.

[damduck-egg]

I had the unit you mentioned above but replaced it with Hoka code 3 when I purchased my first computer that had a hard drive. Lost interest or rather found other things more interesting to do soon after. Only the other day I came across some photos resolved from some News agency facsimile signal showing forces in Gulf war one. checked date ,bloody hell was it really 21 years ago. May still have the kit somewhere but the software came on 5 1/4" floppy which I no longer have a drive for . Wouln't find it that interesting now anyway . I doubt that there is much in the way of photos etc flying around it will all be on satellite now. One of the more unusual intercepts was a wine order from the RMS QE2 back to base . Only thing I ever read in the clear on a signal using Piccolo ISTR.

G.Harman

[Huge]

The best reason of all.

(Although at the moment, you can't.)

[Dave Liquorice]

He he, and add in the facination of a noisey, moving, mechanical device "doing something" rather than a dull, boring, static, laptop.

Anyway the Creed is portable, I can carry it on my own, just (not very far). B-)

And having looked at the price of HF transcievers it may well stay that way... No point in trying VHF or UHF around here either.

[robgraham]

Do single to 3ph 240v inverters work if feeding only a single phase load ? The frequency of them can be varied easily and accurately. Not sure if they go below 0.75Kw, but these are available on Ebay for =A3125, or less if you are patient! Rob

[Ian Jackson]

In message , Dave Liquorice writes

As with the early 'portable' computers - more like 'luggable'.

[Dave Liquorice]

Ahhh... you had an Amstrad PPC as well?

[Skipweasel]

scary thought.

[Nick Odell]

still have a couple of these as well:

with the twin floppies, the other (Compaq Plus) with a 10Mb HD.

Nick