A 160m AM local natter rig

Further to my post a few days ago about possible bands to use for a very local "natter link" over a 3km path between G6ALB and here, my thoughts are turning to 160m, partly for nostalgic reasons. This is where I first started my ham radio operating with a small 400mW AM transmitter from Practical Wireless (Dec 67 I think).

Although 160m is VERY noisy now, especially at night, I figure that 100mW AM will be enough to kill the QRM/QRN over such a short distance. So, I am gathering ideas for something incredibly simple to build.

For the TX the most sensible rig would be a crystal oscillator (or ceramic oscillator) followed by a buffer and series modulated PA using the modulation circuit from the 2m AM Fredbox. On receive, either a regen receiver (operating just out of oscillation) or even an MK484 (like the ZN414) single chip receiver are worth a try.

This would be no DX rig, just a very basic transceiver to get me into the next village and not much further. I'll keep you posted. Incidentally I am unable to do much building right now as my house is in the middle of some redecoration. I can't find anything!

40m regen receiver kit from OK land

OK1CDJ's version of my simple 40m regen receiver

Ondra OK1CDJ has been in touch again recently and he mentioned that he had built a version of my 40m regenerative receiver and is now supplying a kit of parts in the Czech Republic via www.hamshop.cz. There are some nice photos of Ondra's version built into a small tin box.  My original circuit is at https://sites.google.com/site/g3xbmqrp/Home/regen although I admit I was inspired by W2UW who used this circuit before me in his amazing FET-1 transceiver.

Commercial QRP: KX3 or FT818?

CQ Ham Radio Book

As I've said before here,  I just can't understand why an FT817 successor has still not yet appeared. The KX3 pre-release spec (now nearly 12 months old) gives a good idea of what is needed and Yaesu surely could beat Elecraft on price. Also, Yaesu's alternative is likely to win on size and looks.

Here in the UK, once import duty and tax are added, the KX3 will be expensive, so I am still hoping the FT818 will appear soon and be a more cost effective alternative. I love Elecraft kit but not sure that too many over this side of the pond will shell out over £1000 for a commercial QRP radio. An FT818 at, say, £599 would be a more cost effective investment. I say investment as my FT817 is now 11 years old and been the best amateur radio investment I have ever made.

So, I am still on the look-out for some HARD news from Yaesu Japan i.e. specs, price and release dates. If there are any leaks I promise you that the news will appear on this blog as soon as I get wind of anything. And of course, unlike the KX3 I expect an FT818 would be available as soon as an announcement is made.

The image above is linked from http://www.cqpub.co.jp .

Optical cloudbouncing (stage 2)

With my QRSS3 success last weekend over a 3.6km non line-of-sight path at 481THz (red light) I've been looking at other possible NLOS cloudbounce paths that start from my home QTH where I can set up my 100mm optics 0.7W input beacon pointing out of a bedroom window.

There are several different paths out to around 8km away that will be tried shortly.  I need to do a quick check at the RX locations to see that there are no issues e.g. trees very close and that I can safely park the car off the road at night. The tests can't start for a few days as I have grandchildren with us over the weekend. Maybe the first test will be on Tuesday evening.

Simple local ragchewing rigs

The Sixbox 40mW AM transceiver for 6m. Maybe a Fourbox will follow?

The experiments last week by G6ALB and I confirm that to talk over a few kilometres, very little power is needed. Indeed, below 1mW is all that would be needed on any mode, at least on 144MHz. Andrew and I are now thinking about rigs that we can use to simply keep in touch whilst we get on with other QRP tests on bands from VLF to light. One idea is a 4m version of my Fredbox/Sixbox QRP AM transceivers to be called the Fourbox. This would be extremely simple to build and ideal for communication between a couple of stations in adjacent villages. Activity levels on 4m are not that great so we would be unlikely to suffer much interference issues if a super-regen receiver was used as on the original designs. A simple wire dipole in the loft would be fine for an antenna at each end. At 6m I was able to use T37-6 toroids, but at 70MHz I think these would be just beyond their intended design limits. Small airwound coils would probably be OK.

How little power do you need to communicate?

Last night G6ALB and I did a test on 2m to see how little power was needed to communicate between the two of us. Andrew is 3km from me. We both use V2000 triband vertical antennas. We started the test with Andrew using about 0.5mW pep from a simple DSB rig. We then switched to CW (from a decent low leakage signal generator) and G6ALB reduced power in 10dB steps. The lowest level I could still copy his signal was -55dBm which is around 1.8nW. The screenshot above, taken from Spectran, shows his signal at that level.

This sort of power level could be generated by power harvesting, even rectified RF from the HF antenna. Now there's a thought - a free power TX.

Non line-of-sight optical path profile

This is the path profile of my successful 3.6km QRSS3 cloudbounce non line-of-sight 481THz (red light) test on Feb 12th 2012. Sorry it is in feet and miles. The vertical scale is exaggerated, but it shows how non line-of-sight the path was. I used http://www.heywhatsthat.com/ to produce the data. This is a very useful site.  It is fascinating that such paths can be used successfully for optical frequency communications.

A new MF ham band agreed at last

472-479kHz was officially agreed as a new secondary allocation for radio amateurs at WRC-2012 today.  See http://www.arrl.org/news/amateur-radio-gets-secondary-mf-allocation-at-wrc-12 .

It may be some months, or even a year or so, before the band is available in the UK. I already have kit to use on the new frequencies (my 500kHz tranverter) but may update it with a better antenna and a bit more power.

7kHz doesn't sound much but it is much better than the 3kHz available by NoV around 500kHz currently. Also it is likely to be available in most countries with EIRP somewhere between 1 and 5W depending on footnotes and location.

Simple Home-Built Radio Projects page

The website of Rick Anderson KE3IJ is one of my favorites as it is filled with simple circuits, mainly simple receivers, that can easily be reproduced and that work well. See http://www.ke3ij.com/radios.htm. What I like is that on many pages there are little extra bits of circuitry that can be used in other projects too.  Lke me, Rick loves the humble 2N3904 transistor which is useful from audio to VHF.  They appear all over the place in his novel circuits.

The universal scale of things

http://images.4channel.org/f/src/589217_scale_of_universe_enhanced.swf

This quite wonderful website brings to life the scale of things in our incredible universe from the smallest strings and branes to the largest galaxies and nebulae in the cosmos. And we are somewhere in the middle of all this.  Zoom in both directions (smaller and larger) and be amazed.