Friday, 30 January 2015

'29 MOPA / NLOS Lightwave Progress


I've now completed a set of tank coils for the new'29 MOPA project. These were wound with 3/16" copper tubing which has become very difficult to source. Luckily, after much searching, I was fortunate enough to find several rolls locally at a very attractive price. Although I do see it quite often on e-bay, sellers either refuse to ship to Canada or their shipping charges are far too high to make it worthwhile. The larger 1/4" rolls are still readily available, but for any given inductance, will take up a lot more room on the breadboard if space is an issue.

These coils cover the amplifier tank, the Hartley oscillator's tank, and the antenna coupling link. Respectively, the coils measure 4.9uH, 4.0uH and 1.9uH.

Winding these is always fun but the method used requires that the needed length be predetermined and cut from the roll beforehand. The first time I did this, when building my TNT transmitter, I learned the hard way to always add at least another foot to cover the additional length eaten-up by turn-spacing and for coil end flattening and mounting.

While visiting Vancouver for a few days I was able to find a couple of pieces needed for my non-line of sight (NLOS) lightwave experiments.

I purchased a nice 4.25" magnifier lens, with suitable focal length, as well as an inexpensive page-size fresnel magnifying lens. What is particularly pleasing is that the fresnel is a rigid lens, about 2 mm thick, unlike most page magnifiers that are thin and floppy. I have yet to test its blur circle or determine its focal length.

I plan to use one or the other of these lenses in a small, portable lightwave receiver module that I can carry to the other side of the island to listen for the main large transmitter, aimed slightly above the horizon, in beacon-mode. If the smaller fresnel does the job, it will be an inexpensive source for anyone else needing a simple lens for either transmitting or receiving.

If the deep-red light tests prove successful, I'll switch the system to IR light but at this stage I'm not sure how focusing and optimizing receivers and transmitters can be done with a light source that is essentially invisible? Perhaps using an IR source that is right on the edge of deep-red will still have enough visible light to allow finding the optimum focus more easily.

More information on NLOS experiments can be found in Yahoo's Optical DX Group as well is in G3XBM' s 481thz blogs.

As well, anyone in the Vancouver lower mainland (as far as the northern Sunshine Coast area) that might be considering lightwave ... I'd love to work you! Pretty well any high spot in this region is direct LOS for me.


Anonymous said...

Not quite the same as NLOS but nonetheless "Optical DX": 20 yrs back, a Mayne Isl ham named Peter (can't remember call) & I arranged an unusual contact for the June VHF Contest. As I was travelling via BC Ferries that weekend to host a radio show in Vancouver, Peter & I arranged a 2-way contact using mirrors & 2 meter co-ordination. Peter's home was high above Active Pass with an open view to the ferry deck. I took a stick-on type truck convex mirror & my 2M handheld to do co-ordination with Peter. A warm, sunny day made for an easy 2-way contact exchanging callsigns & grid squares as the 'Queen of Nanaimo' rounded Helen Pt & entered Active Pass. We found the highest defined amateur band & gave ourselves each 1 pt for QSO & 1 pt for grid square!!! :-)

Mike VE7SKA on sunny Salt Spring Island

Steve McDonald said...

FB Mike ... Lightwave and marine mobile! Maybe I can get you to build a lightwave RX and look for me on the cloud bottoms!

Greg said...

Coincidently, I picked up the same Fresnel lens at Princess Auto a week ago. Rough measurements indicate a focal length of around 330 mm. I have build the receiver circuit, now waiting the delivery of a couple of PIN diodes, which I though I already had. Next step is the enclosure, which will be challenging.


Steve McDonald said...

Princess Auto is where I bought this one as well... what was it ... all of $3 ? I'm relieved to hear that the focal length is around 30cm which is much better than I had hoped. I was just heading to the shack to measure this one.
Great news on the diodes ... can't wait to run some tests with you when ready. I can put a beacon signal up for you some evening if you wish to play with it. Playing with the RX is a ton of fun also as there are lots of strange sounds to be heard. Keep me posted!