Progress on NE602 based direct conversion receiver

So today I stayed home due to brain pain, it had been building up for the last few days. Also I had difficulty with my balance. To the point that walking involved bumping into everything. Lots of water and pain killers helped a little, breakfast and coffee later helped a little too. However the head ache didn't wear off until late into the afternoon with more sleep. So I spent some of the day sitting down, tidying the shed.

The cool thing about that was I found a couple of little paper bags with parts that I had bought months back and promptly filed for safe keeping in boxes! Anyhow, that list of parts contained an SA602, 3.579MHz crystals, a variable poly-cap, a large breadboard and some zeners.

This was all the missing parts for the NE602 based direct conversion receiver I've been wanting to build. So late this afternoon I sorted out all the other parts, put them in a box and setup on the kitchen table to assemble. My soldering iron and other tools are currently at a friends, so I pretty much had to assemble everything up on the breadboard.



Made dinner, a tasty curry with shallot pancakes. Then assembled it as per the circuit from W1AW. I am not sure where I first found it, google has a few references to it about. There are also a few variations on the NE602 direct conversion receiver, like the MRX-40_Mini_Receiver and another that I like using LC tank circuits for both the RF input filter and the oscillator side.

I fired it up but heard absolutely nothing. Much comparing with the diagram led to adding the vcc and ground rail for the LM386, after which I could hear familiar hash with the speaker held very close to my ear. I dug out the Pixie2 hoping to create some kind of signal. However the oscillator from the Pixie2 did not create the expected signal or inteference on the DC receiver. So this needs looking at another day when I can focus for more than ten minutes at a time. Hopefully this coming weekend wont involve any more headaches.

Kim VK5FNET

More on toroids

Been searching for info about the toroids from Altronics. Setting up a band pass filter for the QRSS receiver.

The L4534 seems to be the same dimensions as the T130-2.

OD = 1.30 / 33.0 mm +/- 0.02 in
ID = .780 in / 19.8 mm +/- 0.02 in
Ht = .437 in / 11.1 mm +/- 0.025 in

Also I've found a useful site on the standard sizes.

The T130-2 has a AL of 11 +/-5%. So then to calculate the inductance like so; uH=(AL*Turns2)/1000

The L4517 does not match up to any of the standard sizes. Its just a bit bigger than the T50-2. So I'll use that as a model and obviously subtract some turns ...

I have three of the L4517's would with 36 turns of 0.5mm enabled wire for an inductance of 12uH. Now to pick out the capacitors for the BPF. Then find the smallest way to build it all up on copper clad board for the Pixie2 in the Haighs tin.

kim vk5fnet

Fun with toroids

The aim here is to find an inexpensive source of toroids for kits for QRSS receivers. Jaycar and Altronics have a reasonable number of shops around the place and also do Internet and mail order, so folks should be able to get the parts easily enough.

Anyhow, some time back I picked up all the 15.2X8.53X5.94 toroid cores, L4517 the local Aztronics. They sell from the Altronics catalog. So these cores are not standard sizes or models that are used in HAM radio, so far that I can make out. They are pretty close to a T50-2, as they are supposed to be iron core, but are a bit larger diameter. Using 0.5mm/24bs enameled copper wire, WW4016, from Jaycar, I've spread the turns out over at least 80% of the toroid, values as follows;

• 10 turns gives 0.001mH


• 20 turns gives 0.003mH


• 25 turns gives 0.005mH


• 36 turns gives 0.012mH - for 3.5MHz BPF

I could probably squeeze on another 5 turns, but 10-36 turns covers the inductance that I need right now. Perhaps other gauges of wire will yield other usable values. These toroids as they are setup are intended for low pass filters or band pass filters. The Pixie 2 needs just one in its current configuration. I intend to build up a better filter as there is lots of AM broadcast signal there when down on the flat in Adelaide.

kim vk5fnet