Friday, October 27, 2017

Test: End fed wire versus AlexLoop on 20m

Recently I did some tests with my two WSPRLite beacons. I started testing my AlexLoop against a 20m long end fed wire on 40m. The wire beat the loop quite dramatically.

One of the comments I got was that the loop should do relatively better on higher bands. That is why I ran a test on 20m as well. I collected the data about 2 weeks ago but due to other commitments I only got around to analysing it today. 

So what was the set-up? As in the previous article, I set up the AlexLoop in the garden with the center of the loop at about 2 meters high. The end fed wire this time was 10 meters long and ran from the back of my house into the garden sloping from about 7m high to about 2,5m high. I ran the beacons on 200mW for 2 consecutive days. 

The WSPR data shows:

  • 514 spots from 49 spotters were received for the beacon on the wire 
  • 436 spots from 29 spotters were received for the beacon on the loop 

This already gives you some impression about the difference. More stations were able to pick up the signal from the wire. 

Looking at the spot map below (distance in km vs SNR) you can see the orange profile of the wire is slightly shifted to the right (higher SNR) as compared to the blue profile of the loop. It is not as big a difference as on 40m though. 
More prominently you can see that the odx is again much higher for the wire as the signal was picked up across the pond in East Coast US (orange spots on the top).

This time the overlap is bigger, which makes it interesting to zoom in on a single spotter to see the actual signal strength over time. I selected one spotter that generated the most spots (EA8) but did check if the profile was any different at other spotters. This seems like a good sample for those stations that heard both. The orange line shows the SNR of the end fed wire, while the blue one shows the loop. On average (also looking at other spotters) the loop is 3 dB down across EU.

There are not enough spotters to make further assumptions about performance differences at specific distances or directions. What you can see is that for DX the signal from the wire is received within a 6dB range of SNR. The loop is not reaching the lowest end of that SNR. So it seems the wire is beating the loop everywhere but more so on DX.

Sunday, October 15, 2017

One man set-up for the 26m Spiderbeam pole

In January of this year I received the Spiderbeam 26m HD fiberglas pole. It is the tallest they have and afaik the tallest you can get. Cool for low band antennas with little compromise.
I used it only a few times as I can normally get all the antennas I have on my 18m pole (or on my aluminum mast) and I simply did not have the time to build and test low band antennas.

When I did bring the mast out I was reminded of its size and weight - 2m when collapsed and an interesting 18kg. If you have a good support - like the one I build that I attach to my car, or some strong fixed pole you can tie the mast to - it is possible to set this up on your own. Otherwise you need more people. When we used it in the open field during the PACC, we need 3 people.

A few months ago I build a simple support system for my 18m pole that allowed me to set this mast up in the open field without any hassle. I have been using this more often and started to think if I could make something for the 26m mast as well. I wanted to use a bigger surface this time, but use a different structure because it would become too bulky if I just enlarged the 18m version.

Walking around in a DIY store I stumbled upon a flat roof vent. The inner diameter is just over 110mm allowing the 26m pole to slip through with the end cap on.

Now picture this thing pressed between 2 layers of wood with holes on each corner for stakes / pegs. I could just see this working. So I took this home and started working on the two layers of wood.

I chose plywood and cut two pieces approx 60 x 60 cm. I chose the bottom layer a bit thicker so I could sink the bolts I was going to use into the wood (and that way keep an even surface). In the picture you can see that I already cut a hole in the middle with the largest hole saw I have. That saw is only 83mm so I next I enlarged the hole.

Enlarger the center hole
The intermediate result - starts looking like what I had in mind

I added 4 bolts though both plywood layers and the metal, made 4 large holes (25mm diameter) near the corners and glued the two layers of wood together. Another thing I did (like with the 18m pole) is to add a fixed ring on the top of the lower segment of the 26m pole and add three guy rings to it.

(sunk) bolts through the wood and metal

Fixed guy rings

I finished the work yesterday, so today I could make good use of the brilliant weather we have at the moment to go out and see if my construction works.

Just for a comparison of size I put the 26m and 18m poles side by side with the two mast supports.

I then started setting up the 26m pole. I used four stakes in the corners of the plate I constructed. They were of different size and mostly too long as you can see. However, they still do the job.

As I hoped, the collapsed pole slipped in nicely and stayed upright - even before I guyed it. That is very convenient as it allows you to add the guy lines one by one and adjust the tension of each one until the pole is fixated and completely vertical. 

I then pushed the segments out with my 20m long end fed wire attached to the upper segment (while I was there I might as well make some contacts). I was lazy and only wanted to assess if my idea worked so I did not guy the pole on any other level. 

As you can see the pole was not completely vertical. This was due to a lack of tension in the guy lines (will put on more tension next time) and of course due to the lack of guy lines higher up. It stayed up though and I was able to make a couple of WWFF contacts in the half hour I was there.

It is easy to set up and break down the way it works now, so I am pleased. The one thing I do need to add is a small step or something else that allows me to stand a bit taller. I am 2m tall but still the pushing out of the last segments is heavy work.

Saturday, October 14, 2017

Test: End fed wire versus AlexLoop on 40m

Recently I acquired two WSPRLite beacons. I want to use them to test various antennas to find out which ones are most effective /P. I have built a number of different antennas and I still have a few projects planned. Modelling antennas gives you an impression what to expect but you only find out in the field what the real performance is. Actually, you need (more or less) parallel reports to account for changing conditions and WSPR is a nice system to get these reports accurately. 

Two identical 200mW WSPR beacons
I started using the beacons at home testing the performance of my AlexLoop against my default antenna - an end fed wire. At home I use 20m of wire that is resonant on 10, 20 and 40m. That wire runs from the back of my house at approx 8m high to a corner of my garden and then still a couple of meters along the far end of the garden - sort of an L-shape. It ends at approx. 1.5m high. Nothing special - not your DX killer.

Although this is a convenient test for me to do at home, the comparison is not that exotic as both a low hanging and sloping end fed wire and a portable loop are realistic /P antenna options.

The first tests I used the AlexLoop in the attic on 20m, 30m and 40m. It turns out that although the loop is higher there, the attic itself attenuates the signal too much. It is just not picked up while I do get spots from the end fed wire. So I moved the loop to the garden at a height you would put it at when going /P - the center at about 2m high.

AlexLoop in the garden
I tuned the loop to 40m. Now spots were coming in for the AlexLoop. Running both beacons for 24h on 40m I can get a good picture of the difference between the AlexLoop and the (low) sloping end fed wire. 

Comparing the spots of the two antennas from the same RX stations, I find that the loop is mostly 10dB or more down from the end fed wire. That is an enormous difference. There is no advantage to be found on any distance for the loop.

Odx for the AlexLoop was EA8 with 3000km (2 spots from EA8) with 39 different spotters over the measurement period.
Odx for the end fed wire was N8 with 6500km (14 spots from W) with 110 different spotters over the measurement period.

The graph above shows the spots for the end fed wire (blue) and the AlexLoop (orange) on 40m over the same measurement period. The distance to the receiving station (in km) is on the vertical axis and the signal strength (in dB) reported by the receiving station on the horizontal axis. 

Apart from the two orange dots at 3000km (EA8) the AlexLoop does not reach much further than 1000km. You can also see that the end fed wire gets better signal reports - with significantly more dots to the right. 

So, my first test of the beacons worked out well and I have my first bit of data on two antennas. My idea is to create a separate section on this website dedicated to antenna performance based on future experiments with the beacons.