35 -> 40Mhz conversion

[stevesey]

All

I've just been looking at the micron transmitter circuits and the idea of a 40MHz conversion (for my JR652 tx) struck me. It looks as simple as connecting a 40Mhz tx module to the trainer lead of the TX and then linking the output to the aerial (with the existing 35Mhz connection and crystal removed). Is it really that easy?

Also I was thinking about building a PIC based mixer unit that would be at the rx end - but equally this could sit between the trainer socket and the tx module.

Steve

[Daniel7866]

All

I've just been looking at the micron transmitter circuits and the idea of a 40MHz conversion (for my JR652 tx) struck me. It looks as simple as connecting a 40Mhz tx module to the trainer lead of the TX and then linking the output to the aerial (with the existing 35Mhz connection and crystal removed). Is it really that easy?

Steve,

-Q1: Can you do that? Probably yes. But!

-Bear in mind that you have to check that the modulation pulses from your trainer plug comply with your 40MHz module. If the servo pulses are "positive" like on the Micron rf input and your module is based on "negative" pulses then your frequency shift is reversed.
-Also on the Micron hf section the pulses are "rounded off" by passing through a filter to minimize sidebands. Do you have a spectrum analyser to check?
-In case you use the stock 35MHz aerial you maybe have to retune the hf coils on the module.
-Last thing: you plan to deeply modify a approved tx. How much can it cost you to certify the new combination and keep you insured?

-Q2: May you do that? It's up to you.

P.S. I did such crazy things over 30 year ago. Wayyyy before Big Brother looks at me.

Cheers,
Daniel

[stevesey]

Thanks

Have been thinking a bit more (dangerous!)

a) If I use a PIC - I can handle pulse inversion here (and other stuff if needs be).

b) I wasn't aware that the standard chrome aerials where frequency specific - but that doesn't matter anyway (see d).

c) I don't currently have a 40Mhz Rx (borrowing one at the moment) and would probably use a matching micron one (avoiding rounding issues).

d) I would proably be easier to build the whole thing (PIC, TX module, Aerial) into a separate (strap on, or belt pack - with stub aerial) box that plugs into the trainer socket on my 35Mhz TX. Avoids messing around with my TX and makes it portable to other TXs.

Cheers

Steve

[vintage1]

It would seem that the easier way is to by an old TX off ebay, and make new elecrronics for it.

I sufccessfully made a 27Mhz transmitter in 1965, though how legal it was remains a moot point.

[stevesey]

Buy stuff!! Actually I've had a re-think. I went back to what my requirements actually were. The model is a hovercraft - with thrust reversers and maneuvering ports - hence the need for non-standard mixing.

a) Multi-channel programmable mixer
b) Minimum model weight.
c) No spagetti of cables inside the model RX -> mixer -> servos

c) was what gave me idea of using the pic to mix the pulse stream itself, as if I do this I only needed an 8pin PIC (one input bit, one output bit). First thought was to do this at the buddy lead point on the TX and then use a separate 40Mhz TX module - my 40Mhz kit is borrowed and will need to be returned.

Anyway I've just realised I can achieve all of this by replacing the 4015 decoder board in a micron receiver kit with a PIC based decoder board. This will need a 18 pin PIC (8 possible output lines - also this means I can use a PIC with 2 16 bit timers and make the software even easier). And yes someone has already done this, see http://www.norcim.fsnet.co.uk/Radio2.htm#J :-)

Result = no spagetti, no extra weight, programmable mixer.

Anyone else have any links to this sort thing?

Steve

[vintage1]

No, but it sounds brilliant.

You can pick up old recievers on Ebay easily for 40Mhz and hack the back ends about.

[stevesey]

I'll probably go for the micron receiver kit, it's only £20, and has separate rx and decoder boards. So I can simply replace the decoder board with a PIC based decoder board - should be easier than hacking an unknown design.

[vintage1]

I take it you are UK then?

I bought a micron off ebay. Not expensive. I think you will have great success.

Mind you, a simple receiver can be had for a lot less than 20 quid on ebay. Nearly all merely require you to pick the digital pulse strem off the input to the decoder - and maybe the reset as well if you need it, and simply take that via a three pin cable to your 'module'

[stevesey]

I'm leaning towards the micron kit because it looks like I should (from the pcitures I have seen so far) be able to fit everything inside the micron case - provided there is enough headroom to allow for the extra height of a socketed PIC.

[vintage1]

Yes, there should be. I dn't realise 'one case' was such an issue though.