E-field probe

My mini-whip E-field probe has arrived from PA0RDT. It will be some time before this RX antenna can be erected as I depend on help these days. It is tiny.

PA0RDT mini-whip

Several people use this very compact antenna on LF and MF for RX. It is an active antenna for receive only. I am thinking of buying one. There was an interesting article on http://www.amateurradio.com/ about optimum height mounting.

Analysis of the PA0RDT E-field probe RX antenna

Image of miniwhip on VK1OD's website

VK1OD has done an interesting analysis of the PA0RDT E-field probe miniwhip receiving antenna. This is very popular as an effective antenna from 8.9kHz right through to the HF bands. I have used my own versions on the VLF, LF and MF bands with great success, but I commend the PA0RDT design to you. His design uses readily available semiconductors to give excellent IP2 and IP3 figures. You may be surprised how something this tiny and simple can work so well if mounted away from the house on a small pole. Remember, you do NOT need big antennas to receive on the lower bands: it is S/N that matters not very low noise figures. VK1OD's analysis is somewhat harsh: in my view it works as a true E-field probe should, even at VLF.

E-field probe tests

This afternoon I built a version of the PA0RDT E-field probe. In the shack the interference was horrendous, but in the garden with the laptop PC just below it the reception of the VLF Alpha beacons and MSK signals around 18-22kHz was excellent. I need to do more noisefloor measurements and elevate the probe higher, but I think this is going to work well when mounted at the top of my neighbours tree that overhangs into my garden. This is a sycamore which I trimmed back a few months ago. The E-field probe can be mounted "in the clear" some 20m from the nearest house at a height of around 5m off the ground. I now need to rebuild it into a watertight box and think how I am going to get the output and power feed to the shack that is at the wrong side of the house some 30m away. Some have used CAT5 twisted wires for this purpose and I guess this would be a good, simple solution, although less suitable if I want to use the probe at 137 and 500kHz where a coax feed would be better.

More on the active LF antenna

Yesterday I used a PA0RDT designed active antenna (but with MPF102 and 2N3904 devices and a 9V supply from a PP3 battery)to listen successfully on both 500kHz and 136kHz. This is a bit better picture of the antenna. Although it is recommended it is mounted well in the clear and away from the house (feeding the power up the coax), I just stuck mine onto my double glazed window - it still worked and heard stations on both LF bands. This is the ENTIRE antenna - no wire is needed down the garden.

In the last few days SM6BHZ has been heard in central Bejing China using a version of this antenna.

136kHz WSPR on an active antenna

Just tried a PA0RDT designed active antenna (but just used an MPF102 and 2N3904 instead as these devices were to hand) with 1m of wire, later just a small piece of copper laminate (see picture), indoors taped to the window and have just spotted M0BMU running 200mW ERP on 137.45kHz WSPR. Amazing that this can work so well. The antenna looks useful for VLF through to low HF. See also
http://carconline.blogspot.com/2009/05/pa0rdt-active-antenna.html and http://carconline.blogspot.com/2009/05/pa0rdt-active-antenna-continued.html