Spark transmitters and modern simple rigs

In the early days of wireless, spark transmitters were all they had. Selectivity and bandwidths were not major concerns.  These days it is all so different with sometimes very crowded bands and the bandwidth of both transmitter and receiver being of major importance.

See http://en.wikipedia.org/wiki/Spark-gap_transmitter for some interesting reading. I recommend you do not try a spark transmitter as you would be very unpopular because of the wide signal and interference caused.   By all means read about them though.

A modern challenge is to see just how simple rigs can be made yet still function credibly on the amateur bands today.  Rigs like the Pixie are fun, but such ultra-simple transceivers are let down by deaf or easily overloaded receivers. To my mind, the receivers have to be selective, sensitive, have netting, and not be easily overloaded. The challenge is to overcome these issues! Often TX power is not the deal breaker.

UPDATE 1740z:  W5OLF has just shown me a photo of his tiny 1 inch ferrite rod antenna on which he has had some success with on 10m WSPR.  I tried some WSPR experiments with ferrite antennas some years ago on 40m, 30m and 20m. As long as the ferrite does not saturate they do work. See www.g3xbm.co.uk .

Sunspots and 10m conditions - Nov 25th 2014

The sunspot number has climbed to 111 today and 10m daytime conditions are again "good". I missed out on 10m this morning until about 1412z, when the band was wide open to the USA, yet again.

472kHz receive here last evening

I receive 472kHz via my transverter but on RX it is totally passive i.e. I receive directly on 472kHz on the FT817 through a series tuned circuit at 472kHz.  Last night, mid evening, 472kHz WSPR was quite busy (see below):

If anything, the FT817 is marginally deaf on 472kHz. This does not seem to be issue though as I seem to hear most of what's going. The "antenna" for the above was the short baseline earth-electrodes: one end is grounded in the flower bed with a 1m long earth rod, about 15m away, whilst in the shack the other connection is to the mains earth. The link back from the far electrode to the shack is 32 x 0.2mm PVC covered wire at a height of about 2m. I am lucky that my RX noise floor is low at this QTH.

On TX last night I was copied by 8 different stations with best DX last night G8HUH (250km). Best DX on the earth-electrode system (on TX with 5mW ERP) is DL-SWL (701km).

10m WSPR-AXE summary

 Just some of the 91 unique spots on 10m WSPR in the last 2 weeks.

My little W5OLF designed "all on one tiny PCB" 500mW 10m WSPR beacon has been spotted by 91 different stations in every continent in the last 2 weeks.

This is the probably the smallest 10m WSPR beacon possible (it fits in a tiny Altoids mint tin), need no PC, and it works remarkably well. It "fits the bill" perfectly on 10m WSPR beaconing for me.

Perhaps I should improve my 10m antenna, but having reached every continent I probably will stick with the 3-band antenna as it gives me so much flexibility. The PAR tri-band antenna covers 10m, 20m and 40m without an ATU.

10m stateside

The first spot in North America of my little 500mW WSPR beacon was by W3CSW (5886km) at 1206z today. My report was -14dB S/N suggesting 10dB weaker (or even less) would still have been enough. Since then, several USA stations have spotted me. I have lost count now of the weeks and weeks the 10m band has opened to the USA and Canada after lunch.

In years to come, we'll look back on these days with envy! In the quieter years it can be a very long time indeed between good E-W openings. At such times multi-hop summertime Es can be the best/only chance of getting to the USA.

UPDATE 1824z:   The last USA 10m WSPR spot today was at 1716z by K9AN (6505km).

472kHz WSPR this morning

As I can now use the FT817 with PC totally separate from my WSPR-AXE beacon for 10m (this needs no PC or separate rig), this morning I continued use of the FT817 on 472kHz WSPR.

G8VDQ (93km) is still being spotted and locals G0LRD and G4KPX are still spotting me. I need to check clock sync.

10m WSPR this morning so far

Using the 500mW WSPR-AXE beacon on 10m, it has just been Europeans spotting me so far. Spots have been from France, Norway, UK and Ukraine. I expect the 10m band will open to the USA for me shortly. The USA is already open for some Europeans.

UPDATE 1216z:   Still no stateside 10m spots as yet.

Bang good portables

There is some confusion over these radios. Although some are limited in the number of channels and some may come pre-programmed, for example, for the  European licence free 446MHz band, several models (such as the ones shown yesterday) say they can be re-programmed in the 400-470MHz range. If so, they would make very low cost 70cms portables.

 On the Bang good website there are even lower cost units for the USA market.

Sunspots - Nov 24th 2014

The sunspot number has slipped a little lower to 66 but 10m daytime conditions remain "good". Some F2 propagation should be expected.

Unbelievable prices!

See http://www.banggood.com/T-688-0_5W-UHF-Auto-Channels-Mini-Radios-Walkie-Talkie-Pair-Black-p-920432.html .

I cannot believe these prices. £13.91 for a pair covering 400-470MHz, 500mW, with free shipping to the UK. That is under £7 each for a 70cm transceiver from Bang good.  Just how do they make any profit? Buy 3 sets and it is even cheaper.  Quite remarkable!

The link says T688 but the photo T668. Not sure which is the correct number but the link works.

The rigs run from 3 x AAA batteries (each) and the price does not include a charger.