VHF/UHF QRP DXing with weak signal digital modes?

When there is a decent contest with some portable stations with decent antennas about, it is surprising how far can be covered with QRP kit on 2m and 70cm. This makes me wonder just what sort of ranges could be covered with QRP and modest antennas on these bands using WSJT digital modes.

Going from SSB to one of the more effective weak signal modes is like gaining another 30dB, i.e. far more that the antenna gain of a big contest station, suggesting that ranges of 200-300km should be ALWAYS possible on 70cms with quite modest QRP stations with small yagis or colinear vertical antennas in flat band conditions.

I am speculating what sort of ranges should be possible under flat conditions (no lifts) with 5W and a small omni or broad beam yagi such as a Moxon or HB9CV.  When I move to the new QTH I think some 70cm skeds are called for with stations out to 300-400km using WSJT modes using 5W or less.

70cm VHF NFD with a simple QRP station

4 ele 70cm yagi on car

Just for a little fun in the sunshine I took my FT817 and "coathanger" 4 el yagi onto a local high spot (actually nothing is high here in East Anglia!) to try just over an hour of operating on 70cm SSB during VHF NFD. Conditions were average, but I heard EI, F, GM and PA and worked 12 stations in just 70 minutes of casual operation with the best DX 262km.  Power output was either 2.5W or 5W.

The 4 el yagi is mounted on a 22mm PVC pipe mast that is simply wedged in the car rear window and manually rotated. The whole set-up can be erected and taken down in about 2 minutes: I don't take contests THAT seriously you see :-)  The map shows the stations worked before going back home for tea.

70cms QSOs in 70 minutes with 5W to a 4el yagi

After tea I parked the car outside my new QTH and erected the 4 el as shown in the photo. Signal strengths from DX stations (PA0 and a station in SW England) were very similar to those on my local /P site, suggesting the new QTH, on a local bump, is promising for VHF/UHF/microwaves.

70cm is a great band and sadly under-used these days on SSB. It is also sad that there are so few 70cms beacons on the air in the UK now. I believe the Bristol 70cms beacon - it was a good conditions indicator here in East Anglia - has recently gone QRT too?

30 line TV

It is a long time since the Baird 30 line TV system was replaced by 405 line and then 625 line TV here in the UK. However, there are still enthusiasts building mechanical 30 line TV systems and getting respectable results. At one time I joined the NBTV group (does it still exist?) who promote(d) hobby activity with 30 line TVs, particularly mechanical versions with scanning discs etc. Bandwidths needed for such systems are very narrow (audio) so the signal can be transmitted using a standard voice transmitter. These days it is possible to produce 30 line TV using a PC, but this not quite the idea: one can after all communicate worldwide by Skype video or FaceTime.

 This video (linked from its original location on You Tube) gives some idea of what is possible.

Wellbrook LF RX Loop

http://www.wellbrook.uk.com/antennashop/image/cache/looponfence-250x250.jpg

A Wellbrook ALA1530 loop antenna for VLF-HF reception is now in my plans for the new QTH. This is not a low cost antenna - currently around £200 in the UK - but its performance is excellent judging by reports from people I know and reviews. It looks like the very best choice of RX antennas for the 136kHz and 472kHz bands where local noise can be a real issue. It does not need to be mounted high, just about 5m from the house. The photo above (linked from the Wellbrook site) shows the antenna mounted on a fence.

The technical specification speaks for itself: truly excellent OIP2 (+90dBm) and OIP3 (+49dBm) figures and a 1dB compression point of +28dBm in the Medium Wave band. It can stand a local field strength as high as 400V/m. As a loop, this antenna has a figure of eight pattern, so local noise sources can be nulled in many cases. It covers from 20kHz to 30MHz.

This looks like a good investment before the LF DX season.

VLF kit at PA3CPM

Henny PA3CPM has been continuing his 8.270kHz VLF transmissions, on and off, for some weeks now and is getting reports from several stations in western Europe despite his modest antenna. Paul Nicholson in Todmorden and Eddie G3ZJO regularly receive his signals using integration over several hours and extremely narrow bandwidths to dig the signal out of the VLF noise.

8.270kHz VLF loading coil at PA3CPM

This is a photo of Henny's huge loading coil used to bring his 40m sloper to resonance on 8.270kHz. The loading coil uses a LOT of wire (several kms) and building such a VLF loading coil is not for the faint hearted! I suspect that a large wire loop may be an easier TX solution?

PA3CPM's VLF PA unit

Henny is using a 200W PA and this is shown here. Note the fans to cool the unit.

To radiate an amateur signal at VLF requires special dedication, yet Henny has shown that even a modest 40m antenna can get a signal hundreds of km on VLF with quite modest powers. It is indeed a new and exciting area of the hobby.

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