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.

More loops

HF TX loop in the bedroom

Small TX magnetic loop performance continues to astound me. This evening I erected my little loop antenna made with 6mm diameter copper pipe and tuned with a standard 365pF air-spaced variable as used in my regen receivers. The loop has a diameter of just 65cm (about 2m circumference) and is mounted on a piece of PVC pipe as a support. The 365pF is attached to the hi-Z part of the coil with a couple of crock-clips. Matching is with a coupling loop about 1/5th the diameter of the main loop.

The simple tuning unit - a 365pF airspaced variable

Without any effort, apart from the tuning sharpness,  it tunes from 10-28MHz and got loads of spots on WSPR. I then tried with 2W CW on 14MHz and received several European reports via the reverse beacon network. The loop is just resting against a wall in the shack. Overnight on 20m WSPR the best report was from 8338km with 2W indoors. On 10m this morning (July 4th) it is already exchanging WSPR spots with CN8LI despite being orthogonal to him i.e. in the worst orientation, 2W and indoors.

According to my loop calculator the efficiency should be around 12% or 9.3dB down on a "proper" dipole antenna on 14MHz. This is less than 2 S-points difference. Results bear this out. On 28MHz the efficiency is better.

Purists will point out that the crocodile clip connections will have a few milliohms resistance and this will reduce loop performance. At 2W there is no sign of arcing across the plates. The point is with QRP one can get away with simple circuits that would not be possible running 100W.

My 1990s station ...and clearing out

Whilst sorting through my collection of SPRAT magazines to give to a local amateur G4NUA - I recently bought the SPRATbook and have most on DVD - I came across this photo inside one of them. It must have been taken around 1992 I think and shows the amateur radio station I had then. What is interesting  is that I actually had a 100W radio (FT747) at that time, although it was hardly ever used at that power because of the problems with RF feedback into the rig. The shack then consisted of a table by the window in our main bedroom. My wife must have been very tolerant!

The 10m Lincoln President, derived from a CB radio, was actually a very nice radio: I recall working mobile with it and having a solid SSB QSO with a station in India early one evening around the 1990 solar maximum whilst driving near Cambridge. It was sold long ago though. The little Mizuho MX2 (I still have one) was used to drive a 10m transverter and I worked plenty of 10m DX with it and around 1W pep to a vertical CB halfwave. The Standard handheld rigs came from my workplace: at one time we were considering OEM-in of PMR radios from Standard (before they joined with Yaesu)  and one of my colleagues got a pile of samples on a trip to Japan. Guess who got some of them after they had been "evaluated"? In the end we got some portable PMR radios from a source in South Korea and that was a disaster.

Today I have far fewer transceivers - all QRP - but get just as much fun. There are no homebrew rigs in this 1990s picture although I did have some. Today quite a lot of my kit is home made, although not all rigs remain in their cases for too long as I tend to note the schematic and take a few photos, then reuse parts and enclosures.

Google Mars and Google Moon

Having played a bit more with Google Earth, I see that you can also view Mars and the Moon too. Quite fun to fly over the Martian and lunar landscapes.

When looking around the Moon tonight I noticed some quite strange markings in one area. Does anyone know what these are?

Again, I have attached a screenshot (Google copyright acknowledged - will remove if told to do so, but Google you are getting yet more FREE publicity for this tool).

http://www.google.co.uk/intl/en_uk/earth/index.html

Path profiles using Google Earth

My thanks go to Richard G3TFX for showing me this Google Earth feature, which may be of interest to VHF/UHF/SHF, microwave, nanowave and SOTA enthusiasts. I had no idea you could do this.

Using the ruler tool (in the menu at the top) in Google Earth click between two places. A line appears together with a distance measurement. Save this as a temporary file in Google Earth. Right click on this file in Google Earth and choose "show elevation profile" and a path profile between the 2 spots appears.

Google Earth path profile

The image above (screenshot from Google Earth - Google copyright acknowledged - will remove if a problem, but you are getting free publicity!) shows the non line-of-sight path between Burwell and the village of Stow-cum-Quy that I managed to span recently with my 481THz QRSS3 beacon using 100mm optics and a TX power of around 0.5W.

This does not appear to take any account of the Earth's curvature, so is probably only useful for relatively short distances. Does anyone know how to factor in this?

Looks a useful facility to me for seeing how close to line-of-sight a moderate length path is.

73s
Roger G3XBM

WiFi extenders?

At the new QTH, the ham shack will be some way from the wireless router and I will not be able to see if the signal will be usable in the shack for some weeks yet; I have yet to organise the move with the internet service provider. (Reminder to self: contact supplier)  Although I could run a network cable through, I'll not do this yet in case the signal proves to be good enough.  It means drilling yet more holes in walls and scrabbling around up in the furthermost reaches of the loft, not something I want to do at my age.

Does anyone have any recommendations for WiFi extenders? Maplin and others advertise these but I am concerned about pumping data along mains cables and the resulting QRN likely to be produced, especially in the lower HF spectrum. Does anyone know of one that is electrical quiet, if that is even possible?

In distance terms, the shack is about 20m from where the router is likely to be located, but the microwave signal will have to get through 3 doors (one is metal) and 3 walls. In the current home the router is upstairs and is a decent signal in the lounge downstairs, but through one more door the signal is non-existent. Incidentally I use a recent Netgear super hub supplied by Virgin Media.

WSPR on an Android or iOS tablet?

A version of WSPR that would run on my iPod Touch 4g or even a version that would run on an Android platform would be a very desirable app. Although there is at least one app for WSPR, this is just a way of looking at the on-line database and not a version of the actual WSPR beaconing software.

I asked this before (back in March), but does anyone know if such a WSPR beaconing app is likely soon, if ever?  Not being a software guru, I've no idea how difficult this would be, but can see a lot of demand for such an app.

Continuing radiated tests on VLF from Holland

Henny PA3CPM continues to fire up his VLF system on  8.270kHz from time to time. Henny has a very small antenna, just a top loaded 14m long sloper but he manages to get 0.6A antenna current and his signal is now regularly copied several hundred kilometres away by people with suitable antennas, preamps and software. Unlike my own VLF earth-mode transmissions, Henny's signals propagate by radiation. He is a shining example of what can be done with a modest set-up on the so-called "Dreamer's Band".  It is no mean feat to radiate a decent signal on VLF with such a small antenna. I have asked Henny for photos of his VLF TX, antenna and loading coil.

Ultimate 2 QRSS beacon TX

The Ultimate2 QRSS kit

The latest edition of SPRAT, mine arrived yesterday, reminded me that G0XAR and G0UPL have produced a very nice QRP beacon transmitter for weak signal modes including QRSS and WSPR. This unit can run stand-alone without tying up a PC to generate the WSPR message, although a GPS module is needed to get the WSPR time sync. The beacon will work on all HF bands with a suitable low pass filter and do other modes like QRSS too. There is even a version that can do WSPR and QRSS in alternative time slots.

See http://www.hanssummers.com/ultimate2.html . At just £17.50 this is a great value kit for those interested in weak signal beaconing.

Earth-mode transmitter on my website

I have added a page on my main website showing the VLF earth-mode beacon transmitter currently being used. In the next few days I'll add the article that appeared in RadCom in 2011 which shows the schematic as well as some more details of the recent tests.

At the moment, my earth-mode tests are on hold. I am finding more and more of my time is being taken up preparing for our house move. At some point in the next few weeks it will be time to take down the V2000 VHF/UHF vertical and the other antennas. It is a long time since I've had no antennas up at all! With luck I'll soon have them back in place at the new QTH and I can start DXCC chasing (gently!) from scratch again. I wonder how long it will take to work my first 100 DXCC countries with modest antennas at the new QTH?

The new home has a totally different shape garden and I shall be intrigued to find out how well (or not) an earth-electrode antenna works on VLF, LF and MF. A 20m baseline spacing between electrodes should be possible by placing the remote electrode at the far corner of the garden with the feed wire diagonally across the garden.