Archive for the ‘antenna’ Category

W3EDP Antenna

My QTH isn’t great for antennas. I’ve tried a few types but haven’t managed to find one that works for me, especially on the lower bands like 40m and 80m. About 2 years ago I made up a W3EDP antenna using some left over wire and a 4:1 balun. It was noisy and worse than anything else I had kicking about. So back in the box it went.

I thought I’d give it another go as domestic planning permission has been relaxed a bit. There are a few different configurations of the antenna but they follow a similar path. A long, not particularly resonant, antenna made up of a long element and a counterpoise.

 

In my case I followed the ‘ladder line method‘ where the antenna and counterpoise are as a single piece of ladder line for 17ft and the remainder antenna wire is just normal wire. So it looks like the original Zepp antennas and a little bit like this

 

The diagram above gives an additional component to the ‘normal’ W3EDP antenna. that is an additional counterpoise. I thought I’d give this a go based on a bit of background reading I did. NC4FB explains his experiences with the normal design and I have to say I had similar experiences. Namely that the swr was quite high and it was not that easy to get it down to usable levels on any of the bands when the antenna was first played with. A good idea to try my own extra’s.

So, test gear is as follows.

Antenna connected to homemade 4:1 balun with some mini 8 coax (about 7m) hanging outside a downstairs window. Antenna raised in a V shape with the balun box at ground level and the antenna supported about 1/3 of the way down on an aluminum mast approximately 8m off the ground. The end of the antenna is resting on the fence at about 1.8m off the ground. Hardly ideal but good for enough for a lash up.

I used a MR100 Antenna analyser. These are cheap and good for indicative measurements. There is also some good free software available to use with you Linux PC (There are probably windows varieties but I didn’t look).

I did 4 tests. Vanilla, i.e. no extra counterpoise. A 32ft counterpoise, A 16ft counterpoise & lastly an 8ft counterpoise. The outputs are below.

No additional counterpoise

 

32ft counterpoise

 

16ft counterpoise

 

8ft counterpoise

So what does this tell us?

Actually that there is a good argument on the face of it to add in an additional counterpoise. The 32ft one has a greater effect on the lower bands and the short on the higher bands. Nothing too contentious here then. So what happens if you connect them all up together.

It does lower the swr but that is probably not the only effect. I think this might need some extra experimentation or at least a bit more digging to see how to improve the antenna for my qth. But for now I’ll sort the lash up out and give it some on air testing.

Indication versus measurement

The nature of a technical hobby gives way to the ‘buying of stuff’. Sometimes this is the tool required to carry out the crux of the hobby, in our case I’m referring to the transceiver. Sometimes this is the tool required to check that the main tool is working correctly, in our case this could any number of tools such as an antenna analyser.

There are also many hams that like to buy the box, or series of boxes and do the minimal amount of testing to ensure safe operation and there are those that will only operate what they have built themselves. Most of us fit on that spectrum. I certainly do, it just varies on what I’m doing.

For longer than I care to admit I have used an antenna analyser that belongs to my local club. It is free to be loaned but I’ve used it more than my fair share of times. I also like to build the odd antenna. This means I measure the length and then cut the wire and check it’s various characteristics and generally cut it again until I’m happy that I have a suitable compromise. Its a really useful tool. I assume its quite accurate because it cost a lot. But do I really need it?

Separating needs from wants is not that easy, partly because what starts out as a want can quite easily become a need. I made a decision recently, I was going to buy my own analyser. But which one? Que the usual looking through specs and performance criteria, guess what happened next. I started with a small requirement for a HF analyser and ended up looking long and hard at analyser >£300. Reflecting on this it becomes easy to bump up the needs because I never really noted down what I actually wanted.

So what did I actually need? In this case I wanted to ensure that I wasn’t going to damage a transceiver and transmit spurious rubbish (as opposed to my usual cw rubbish). So I didn’t really need a tool to measure, I needed a tool to indicate. But ah ha, I still needed to cut the antenna to the right length, so I did need something to measure but did it need to be really accurate?

It turns out it didn’t. It’ll be a good idea to get a rough idea but to 3 decimal places? nope, it just isn’t that important. So I duly purchased a cheapo SARK analyser off ebay for around £30 and it’s allowed me to measure and get the right length(s) (I built a multiband end fed antenna this time) and use a cheapo end fed tuner and the analyser to get the correct swr and impedance for safe and fairly optimised operation.

The lesson learned is that if I don’t set out the requirements first then I’m going to end up spending 10 times on a product that I probably don’t need.

Comparing two antennas with WSPR

Ultimate 3S with 5-band relay module in front,
variable LM2596 power supply (with voltmeter) for
the power amplifier behind left,
a variable LM2596 supply set for 5 Volts for the Ultimate 3S
in the middle, and the antenna switch to the right in the back.

WSPR – The system for Weak Signal Propagation Reporter makes it easy to compare antennas if your transmitter can instantly switch antennas. The system shown here can send on antenna 1 for almost two minutes and then switch immediately to antenna 2 for the next transmission.

The Ultimate 3S already has software that supports that and application note 3 from QRPLabs (Controlling additional relays using the Ultimate3S “Aux”) describes how. I built mine following that note and the experience from EA1CDV.

The circuit is controlled from pin D7 and consists of a transistor, a relay, a resistor and an electrolytic capacitor. In addition I have two LEDs that indicate which antenna which is in use. In the first picture the green LED in the back right under the BNC antenna connector shows that antenna 1 is connected.


In the next picture, the whole layout is shown a little better. In this case LED 2 is lit, the faint yellow one. It sits right under the additional SMA antenna connector in the top left-hand corner that I had to fit.

I have used this setup for a few days now on 7, 10, 14, and 18 MHz with some crossed doublet antennas (somewhat like this setup, but not in the same location). I change the frequency between antennas, e.g. 50 Hz below the center frequency of the band for antenna 1 and 50 Hz above for antenna 2 in order to simplify discrimination between the transmissions.

The short 13 m antenna transmits best East-West, and the longer 26 m antenna North-South. The directivity is in general confirmed by the WSPR reports I see. Sometimes the difference can be more than 10 dB in SNR, but more often it is closer to 5 dB. But it also happens that only one of the transmissions is detected. This should make for some interesting analysis in the coming months.

The post “Comparing two antennas with WSPR” first appeared on the LA3ZA Radio & Electronics Blog.

Comparing two antennas with WSPR

Ultimate 3S with 5-band relay module in front,
variable LM2596 power supply (with voltmeter) for
the power amplifier behind left,
a variable LM2596 supply set for 5 Volts for the Ultimate 3S
in the middle, and the antenna switch to the right in the back.

WSPR – The system for Weak Signal Propagation Reporter makes it easy to compare antennas if your transmitter can easily switch antennas. The system shown here can send on antenna 1 for almost two minutes and then switch immediately to antenna 2 for the next transmission.

The Ultimate 3S already has software that supports that and application note 3 from QRPLabs (Controlling additional relays using the Ultimate3S “Aux”) describes how. I built mine following that note and the experience from EA1CDV.

The circuit is controlled from pin D7 and consists of a transistor, a relay, a resistor and an electrolytic capacitor. In addition I have two LEDs that indicate which antenna which is in use. In the first picture the green LED in the back right under the BNC antenna connector shows that antenna 1 is connected.


In the next picture, the whole layout is shown a little better. In this case LED 2 is lit, the faint yellow one. It sits right under the additional SMA antenna connector in the top left-hand corner that I had to fit.

I have used this setup for a few days now on 7, 10, 14, and 18 MHz with some crossed doublet antennas (somewhat like this setup, but not in the same location). I change the frequency between antennas, e.g. 50 Hz below the center frequency of the band for antenna 1 and 50 Hz above for antenna 2 in order to simplify discrimination between the transmissions.

The short 13 m antenna transmits best East-West, and the longer 26 m antenna North-South. The directivity is in general confirmed by the WSPR reports I see. Sometimes the difference can be more than 10 dB in SNR, but more often it is closer to 5 dB. But it also happens that only one of the transmissions is detected. This should make for some interesting analysis in the coming months.

The post “Comparing two antennas with WSPR” first appeared on the LA3ZA Radio & Electronics Blog.

Inverted L

I have been lacking the ability to operate on the lower HF bands, while my small 'multi-band' OCFD could be used on 40m trying to use it on 80m was nigh on impossible with my ATU. As you would expect even if matched for a useable VSWR the actual performance has been compromised.

I needed a cheap and relatively unobtrusive solution and I found one in Len Paget's (GM0ONX) design for an inverted L. The full details were printed in the Practical Wireless magazine several years ago and PDFs are available for download from Len's website. The designs make use of coaxial traps, one for the 80m version, two if you want to add a top-band (160m) option.

Opting for the smaller 80m version I set about building one. Using an old fibre-glass fishing pole about 5m high at the far end of the garden tucked behind the summer house which I could collapse down and then retract the wire elements when not in use so hiding it from view.

The fun and interesting part was building the trap. They are formed by coiling some coax, in this case RG58, round a former such as plastic waste pipe. I had a bit of scrap pipe but it was 32mm not the 40mm diameter type described in the article, thinking it couldn't make 'that much difference' I built one using the same number of turns but the resultant antenna wasn't anywhere near resonant according to the analyser.

I decided I needed to test the trap's frequency response. I found a YouTube video by Dave Tadlock (KG0ZZ) where he demonstrates using a MFJ 'Grid Dip Meter' adapter on an MFJ antenna analyser to test coaxial traps.

The adapter consists of nothing more than a coil of wire on a suitable former so I made my own to use with my AW07A analyser. It worked a treat and I discovered my trap was way off frequency. In the mean time I had located a useful PDF document by David Reynolds (G3ZPF) which informed me I actually needed 180cm of RG58 round a 32mm pipe to make a suitable 7MHz trap, so I made another.

I made a small video showing the traps and how I tested them.


The resulting antenna seems to perform well, but it does sag a little due to the weight of the trap and wire and the flimsiness of the pole. But I have made a number of contacts on it and used it during the RSGB 80m CC Datamode contest a few weeks back. It was my first go at this contest but once I got the hang of operating it was great fun.

Inverted L

I have been lacking the ability to operate on the lower HF bands, while my small 'multi-band' OCFD could be used on 40m trying to use it on 80m was nigh on impossible with my ATU. As you would expect even if matched for a useable VSWR the actual performance has been compromised.

I needed a cheap and relatively unobtrusive solution and I found one in Len Paget's (GM0ONX) design for an inverted L. The full details were printed in the Practical Wireless magazine several years ago and PDFs are available for download from Len's website. The designs make use of coaxial traps, one for the 80m version, two if you want to add a top-band (160m) option.

Opting for the smaller 80m version I set about building one. Using an old fibre-glass fishing pole about 5m high at the far end of the garden tucked behind the summer house which I could collapse down and then retract the wire elements when not in use so hiding it from view.

The fun and interesting part was building the trap. They are formed by coiling some coax, in this case RG58, round a former such as plastic waste pipe. I had a bit of scrap pipe but it was 32mm not the 40mm diameter type described in the article, thinking it couldn't make 'that much difference' I built one using the same number of turns but the resultant antenna wasn't anywhere near resonant according to the analyser.

I decided I needed to test the trap's frequency response. I found a YouTube video by Dave Tadlock (KG0ZZ) where he demonstrates using a MFJ 'Grid Dip Meter' adapter on an MFJ antenna analyser to test coaxial traps.

The adapter consists of nothing more than a coil of wire on a suitable former so I made my own to use with my AW07A analyser. It worked a treat and I discovered my trap was way off frequency. In the mean time I had located a useful PDF document by David Reynolds (G3ZPF) which informed me I actually needed 180cm of RG58 round a 32mm pipe to make a suitable 7MHz trap, so I made another.

I made a small video showing the traps and how I tested them.


The resulting antenna seems to perform well, but it does sag a little due to the weight of the trap and wire and the flimsiness of the pole. But I have made a number of contacts on it and used it during the RSGB 80m CC Datamode contest a few weeks back. It was my first go at this contest but once I got the hang of operating it was great fun.

Just the medicine for lowering impedance

Pill bottle balun

Jack-WD4E is a fellow NAQCC member and he sent me one of his QRP creations that I just had to share.

If you are staying on your meds you probably have the perfect enclosure for a QRP Balun.

If I could save RF in a bottle...
Jack encloses his home-brew wound toroids in pill bottles.  
The child and arthritis proof cap keeps the goods away from young and old alike...


Just what the doctor prescribed...



So re-purpose your medicare paid goodness and put it to work for you

Sorry all you entrepreneurs, Jack told me that he's already applied for the patent so you won't be competing with Facebook with this product idea.  He owns it.


That's all for now

So lower your power and raise your expectations

72/73

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