Miles and miles of nothing!
I was going to title this ramble "It Shouldn't Happen To A DXer - Skegness Edition" as some of today's experiences reminded me of the disasters which occurred when Beveraging it out in Nottinghamshire and Derbyshire. You can read about those by clicking here.
For those who don't know what a Beverage antenna is, it's a very long 'longwire' or 'wave' antenna, principally used for receiving on the medium and short wave bands. It was created by Dr. Harold Henry "Bev" Beverage from North Haven, Maine in 1921. It is also used in amateur radio and military applications. More about it here.
This little radio trip should have happened two months ago but the 'one thing after another' law has prevented me from doing this. It's a law most of us live our lives by and can be very frustrating. Part of the problem was that everything was done 'last minute', as is often the case. I am late for everything. I wonder if I will be late for my own funeral, as the saying goes. I was 20 minutes late for my own wedding, so there's every possibility.
Altocumulus above The Wash
"It's 10am and I think I will make that Beverage trip this afternoon! Now then, I need to be set up for 1300 to catch any early fade-in of exotic Asiatic DX." Ha! The clock has rolled on to 11:30 am after getting a bite to eat. My wife asks me to go to the shop, not for a pint of milk and a loaf of bread. No! For a whole week's shopping (almost). I rush to the shop and back as quickly as I can, forgetting half the things I went for, but I got the most important things so she is reasonably happy. It's now 12.00 midday and I haven't even started to sort out the gear. I think I'd better forget the 1300 slot.
A quick sort through the gear I will be taking and packing it in the car has me wondering what I might have forgotten. There's bound to be something. Earth rods! "Where are the earth rods?" I never found them and so had to bodge some short lengths of copper plumber's tubing, one only eight inches in length, and some crocodile clips to clamp the wire to the tubing. Oh dear! This is turning into another of my "Bodgitt & Scarper" routines.
12:30 and I am setting off. That's after getting out of the car and going back into the house THREE TIMES to fetch things I had forgotten. I arrive at The Wash at 12:50 to find a few dog walkers at the spot but they disappear in minutes. I don't like to roll out hundreds of metres of wire and bash copper tubing into the ground with a hammer with people watching. Occasionally I am approached by members of the public who ask me what I am doing. The answers don't come easily. I just inform them that I am a radio ham and I am doing some listening or antenna experiments. That usually has them running.
The beverage antenna and coax feed is already to be rolled out from a plastic garden hose winding device. It weighed a ton because it already had about a km of thinner wire underneath which I used last season. That proved to be useless as there it was far too thin and produced too much resistance along its 380 metre length. There was also 100m of RG58 on this reel so you can imagine the weight. I deliberately kept all this on the reel as it would create a larger diameter base on which to wind the new beverage wire, and so wind it on more quickly after use. The 'new' wire, much thicker military specification field telephone wire, was obtained from Anchor Army Surplus in Nottingham a few weeks earlier. It is two core and I decided to connect the ends together to further lower any resistance.
For some reason I had thought there was a fence at his location on which I could suspend the wire and make a proper beverage, rather than just running it along the ground. There wasn't!
Freshwater Marshes
From the car, 50 metres of RG58 goes out to the balun box, which contains a binocular core and a 3:1 turns ratio of enameled copper wire. This gives inductive coupling to the antenna and cuts off the electrical noise from the car. Believe me, my car emits a huge amount of noise, even when you think everything is switched off! A copper earth rod (the eight inch excuse for one) grounds one side of the primary coil while the other side of that goes to the Beverage wire itself. I didn't trim the Beverage wire (and had no idea of how much was on the reel) and discovered it was approximately 370 metres in length. Perfect! The far end of the Beverage wire was terminated straight to earth as I ran out of time to wire in a terminating resistor. Once again I adopt the Bodgitt & Scarper technique of binding the wire to the copper tubing (this one's about two feet in length!) with a strong crocodile clip.
A Beverage on the ground has a low terminating resistance, something around 200 ohms I believe, and so running the far end of the wire straight to ground should not be a big problem. I had asked my wife, a ham herself, to come along with me today so I could make a better job of the termination resistance, using 2m walkie talkies to make the adjustments, one of us at the receiver, the other making adjustments to the resistor. She declined since there was some awful film on the telly she wanted to watch.
Sunset, looking south-west
It's approaching 1400. The Beverage is in place. I am sat in the car, Perseus recording, and I see that the computer clock is several minutes fast. Damn! I update it while listening to the time signal on BBC Radio 4 198 kHz. At least the time will be correct for 1500 hours after another adjustment.
Conditions were rubbish at 1400 so I took a walk along the length of the Beverage to make a better job of the connections, though everything seemed to be working perfectly well. While I was out I came across some dog walkers and was mauled by two little Fox Terrier doggy type things, resulting in lots of mud all over my jeans. They had a third dog. A much larger one which thankfully left me alone. Instead, it took a keen interest in the Beverage wire. No fear, it's tough stuff so I can't see the dog causing any damage to it.
1500 came and it was back to the car and the next Perseus recording. This all passed uneventfully. I could barely hear Urumqi on 1521 so I just had to put it down to very poor conditions, but I was expecting this anyway. At least I could now do some more experiments with the Beverage.
Perfect location for a Beverage!
Time to relax now since conditions were rather rubbish. The next exercise was to remove the balun to see if it made any difference. Wow did it! Noise returned across the whole band, largely produced by the laptop power supply. The noise was strong enough to render even good signals unintelligible. Noise levels were evenly down to -135 dB with the balun in place, according to Perseus. That's VERY quiet indeed. Too quiet perhaps? I have more signal at home on my flag antenna! Can that be right for a 370 metre Beverage?
Off to the end of the Beverage next to experiment with the terminating resistor. I had one with me, ready to put in place. Perseus was still recording so I could hear the difference on playback. On reaching the end of the wire I discovered it was open ended as it had been pulled away from the crocodile clip, possibly by the aforementioned large dog. Still, I intended to make some 'before and after' comparisons with the wire being earthed and then not earthed, and then with the variable resistor, everything synchronized to the clock so I could check things when I returned home. Unfortunately, on checking the recording of the terminating resistor tests I found that there was no audio on that file. The previous file had audio and you could hear and see the differences with the wire earthed and then not (very little actually) but the following file with the variable resistor test was just five minutes of silence!
More nothingness!
So what did I learn today? Hmm. 1. The most striking thing was the beautifully quiet band when the balun was in place. 2. The termination resistance of a Beverage on the ground might not be necessary. Just put the far end of the wire straight to ground. 3. Conditions to Asia were awful! and 4. Set out earlier next time.
Here's a short file from the 1500 slot to demonstrate how quiet the antenna is. Just don't expect any DX!
File: http://www.mediafire.com/?umvrydt3na8qr
PS: I would like to add a quick 'shout' for a couple of Yahoo Groups which have been a huge help to me over the last few years. They are the Beverage Antennas Group and the Real DX Group.
The former, as the name suggests, is a dedicated group of people who have a wealth of experience with Beverage antennas. They recently helped me with a couple of questions I had regarding these antennas.
The Real DX Group helps people who have recordings of unidentified DX. Their membership is truly global and the extensive language skills and general knowledge of broadcasting the world over means they can often identify your unidentified DX. Both groups are very helpful when it comes to newcomers too, but as with all groups of this kind, your input could be very useful too. Please support these excellent groups.
Good DX!
John
What was the end to end resistance of the thin beverage wire? If the thin wire was made from copper a more likely reason for the beverage not working could be a break somewhere. . .
ReplyDeleteYou may be right over the far end earth being sufficient termination, but it sounds a bit hit and miss. A small earth rod in normal ground could have an earth resistance of several hundred ohms. If space at the end is available you could try adding one or two sets of diametrically opposed identical radials each 30-50ft long to supplement a short earth rod, and terminating against that.