Saturday, May 08, 2010

Building an AM transceiver kit for 80m

I'm having a lovely weekend building the "Retro-75" kit from Small Wonder Labs.

It's an AM transceiver ostensibly for the US 75m band but easily moved to our 80m band. I'm running it on a 3.58MHz computer crystal.

Step one was to clear the bench in my "shack":

1 clear bench.jpg

I started construction with the smaller components, resistors first then capacitors:

2 fit components.jpg

The board is excellent quality.

3 capacitors.jpg

I didn't rush but it came together over two days without much trouble save my own sloppiness.

4 coming together.jpg

For me the shack is a real haven away from domestic life. I must spend more time there.

5 the shack.jpg

The kit is missing a few parts on the receive side which Small Wonder Labs will post when they have them in stock - they are T1 & T2 inductors used for the front end and near the detector, I should be able to rig something up until they arrive.

At this point it's transmitting and putting out a solid 2W. I called up local ham Rob, VK2ZNZ and had a first contact.

6 First contact.jpg

Initial reports are rather distorted audio, my guess is RF feedback, so I'll start looking for a suitable metal enclosure and see if that improves things.

A great kit, thanks Dave K1SWL. There is a Yahoo group where constructors discuss the project and Dave has announced that he has the missing components.

Anyone interested in an AM net on 3.58MHz?

Update

The modulated audio is very distorted. Tracing from the mic input with a tone connected I see clean audio after the pre-amp (pin 1 of U5). I've clipped the collector of Q10 which disables the audio AGC and now things look much better. Not sure what's going on there..

Update 2

Peter, VK2EMU, very kindly sent me a crystal for 3.6864MHz so I can participate in the AM net. Although this crystal is a common computer frequency, Jaycar no longer stock them, they do stock some nice boxes so the rig is now in a case:

boxed retro.jpgUpdate 3

The missing IF transformers arrived and I'm now receiving. Had to remove 3 turns from L2 to get the receiver centred on my target frequency of 3.6864. Tuned up very nicely and now I'm hearing sideband stations and static crashes - not super sensitive but probably quite enough for contacts who can hear my 2W.

It's been a really fun kit, very easy to put together and get going.

1 comment:

Anonymous said...

Coffee, solder smoke and a sunny window, what more could you ask for?
Nice kit Peter, looks like a lot of fun to build.
Cheers and 73s