Ferrite Rod RX antenna for 472kHz

 In an attempt to overcome my high LF noise level, today I made a small ferrite rod antenna and preamp for 472kHz which I've been trying out on RX. The ferrite rod was just a small 10mm diameter 60mm long rod (i.e. it is a small ferrite rod) tuned with a 365p variable capacitor and fed into an MPF102 gate at high impedance with the output fed to the FT817 via an emitter follower. At the moment the rod is sitting on the bed in the shack. Despite this, it is picking up WSPR from DK7FC.

I shall have to try a larger ferrite rod next and try placing this remotely in the garden away from noise sources. For a first attempt this is encouraging.

The prototype used to receive DK7FC and G3ZJO

UPDATE: later I tried the 60mm ferrite rod and preamp on 500kHz and copied G3ZJO on several occasions. 

MF "swish, swish, swish" interference

In recent months I've been suffering from man-made noise on MF which was not there before. I've a constant S8 noise floor now (it was around S1-2 before) and as I tune from 300-500kHz I get a rapid  "swish swish swish" every few hundred Hertz. I think there are frequencies where it is stronger but the new 472-479kHz is BAD, although I still manage WSPR decodes from DK and SM. For CW it would be just about impossible.

Now, I haven't yet tried to systematically work out what this is yet and nor have I tried a small external loop on RX or an E-field probe down the garden.

Before I start to investigate, does anyone have a clear idea what this rapid "swish swish swish" QRM is likely to be? I don't think the source is in my own house and on one side the neighbour's house is currently unoccupied. I have tried the obvious (turning off lights and SMPSUs in my own place) with no success.

Any knowledgeable help would be much appreciated.

Man-made interference at MF and LF is a critical consideration for newcomers. I hope that a new version of the RSGB book "LF-Today" (if one is planned) will give some information on how to search out such sources and some strategies for how they might be mitigated.

Building requests

In the last 24 hours I've had a couple of requests from people asking me if I'd build some of my projects for them. One person asked if I'd build them a Pipit 15m transceiver and another a 472kHz transverter. Regretfully I had to say sorry that I could not.

It is not that I don't want to. Rather, it is because I don't have enough spare time! I've so many projects on the go currently, and a stack more in my head waiting to get started, as well as trying to live a normal family life doing the usual chores. Then we have the grandchildren who take time, not that we mind this at all.  So, please do not ask if I can build projects for you. I always try to help with advice and suggestions when asked - I try to respond within 24 hours unless I am away -  but I do not want to do building.

Quite a few of my projects would benefit from a small PCB. This is also something that I rarely get around to because I've already moved on to something else. There is probably a small business possible, if I was inclined, designing projects, making a PCB and selling kits. This is unlikely ever to make me rich though and I'd prefer to be a source of ideas instead.

Norway on 4m

The Norwegian authorities have granted further access to parts of the 4m band (70.1875 - 70.2625MHz), with some regional limitations. This is great news for 4m where more and more countries are now gaining access. The following chart on the Four Metres Website (I've linked to it here) shows the countries with 4m allocations currently.

Norway gets 472-479kHz right away

Norway has been granted immediate access to the new MF band with CW and all digital modes permitted. See  https://www.nrrl.no/318-news/latest-news/492-lb1g .  I hope some LA stations come on to WSPR in the new band this evening.

More 474.2kHz WSPR

This evening I am copying 3 stations, so far, on 474.2kHz USB dial WSPR: SM6BHZ and DK7FC are both good signals with QSB but I've also copied DL3ZID at -27dB S/N. QSB is slow and it takes about 12 minutes for DK7FC's signal to go from -27dB S/N to -12dB S/N.

Lesser Chirpy 10m transceiver

You may recall that some months back I did a tiny transceiver for 10m CW ....that chirped. Well, this is the latest version that does NOT chirp! Instead of keying the oscillator current, I now key the capacitor that sets the oscillator frequency instead i.e. FSK keying. The latest version is shown here. Have a go: 10m is is good shape and you may get a few QSOs.

If the going gets tough (the RX audio level is low!) try adding an extra antenna change-over switch so you can receive on an external receiver instead. or add a 100n from TR2 collector and feed the signal into a sound card and SDR so you can use the PC's audio gain to help with copy and tune either side a few kHz.

472kHz transverter (rev K)

Several people have now built versions of my 472/500kHz transverter. The latest version is shown below which includes provision for an additional low pass filter when using a fairly long (less sharply tuned) antenna. Although some capacitors could be combined to reduce the component count, I've shown it using readily available high voltage capacitors. The 16uH inductors are 43turns of 0.71mm wire on 22mm white PVC pipe.

In the last few minutes I've been looking on 472kHz WSPR and see that SM6BHZ and DK7FC are coming through OK despite my S8 noise floor.

SM6BHZ and DK7FC this afternoon on 472kHz WSPR

December's Practical Wireless

The December 2012 edition of "Practical Wireless" has my article about the 2m AM Fredbox and the 6m AM Sixbox transceivers that are described in more detail on my website. These simple QRP VHF transceivers proved to me that you don't need to spend lots of money to make simple transceivers that work. Both have produce interesting QSOs: the 2m Fredbox had several 90km QSOs with one at 160km, despite being only 10mW output and using just a whip antenna!

Today there is not that much AM activity on the bands but I think this is a great pity as the mode has a lot to offer. I do hope the RSGB can be (eventually) persuaded to add 144.55MHz as the AM calling/working frequency in the band plan. It is mentioned (almost lost) in the foot notes, but it needs to be properly shown. For some reason the RSGB seems to have a problem with 2m AM.

I hope others will build simple AM gear for 144.55MHz or crystal up some ex-commercial PMR radios and again enjoy the fun of 2m AM. Second hand AM gear for 4m and 2m can often be obtained for just a few pounds as no-one wants it.

GPS Route Logger

Last week I bought a Ventus G730 GPS Route Logger from Martin Lynch for £34.95. Today I tried it out for the first time on a walk in the bright autumn sunshine at Ickworth park, near Bury St Edmunds. I am totally delighted with it.

The map below shows the route taken as plotted on Google Earth. The data that comes out of the logger shows route taken, speed (average and instantaneous) , distance traveled, and altitude up and down. If linked to a digital camera file it can be used to geotag photos on a walk. I am very impressed that something this small shoved in your pocket can produce such fun results. I now need to find a use for this in my amateur radio experiments.

Google Earth plot of a walk today using data from the Ventus GPS logger