RaDAR – From dipoles to end feds to multiband end feds

Sometimes antennas just add to the confusion.

Once you think you understand the very basic basics of antennas then you start to realise how little you know. The Internet is a minefield of information too and your gut feel has to guide you in the right directions. I browsed the Net for suitable diagrams which hopefully the authors will not mind me sharing here. I like simple, simple is good!

The dipole

Although here in South Africa we use the metric system I still remember this formula from many years back. Also the wires being horizontal the general feedpoint impedance has always been known to be more than 50 ohms …. actually I had 75 ohms in mind.

Here the feedpoint impedance comes closer to 50 ohms in the inverted vee configuration. Radiator lengths change somewhat too! Aha there is a formula for METERS !

At one stage in my ham career I tried the windom antenna, with little success I might add. Same formulas being used to calculate the length of a half wave dipole in feet. Only here, the feedpoint has been shifted to one third from one end and the feedpoint impedance is at a point where it’s around 300 ohms (Or is it 200) thus needing a 4:1 balun to match this impedance to the 50 ohm coax of the transceiver. Now also, the “dipole” has become multiband?

The Windom

Then a few years back I started using end fed antennas because of their rapid deployment ability in the field. Here the feedpoint is shifted to the end of the dipole where the feedpoint impedance becomes a guess at best but is theoretically around 3000 to 5000 ohms. These antennas are better than using a 1/4 wave vertical which requires a ridiculous number of radials in order to work efficiently.

I built the manually tuned Fuchs tuner which allowed a certain amount of multiband functionality using a half wave length of wire for the lowest band used. It took me a while to build but worked well. Why I took it apart again is still a mystery! Maybe it was too big for my RaDAR backpack.

I also built a “fixed tuned” 40m end fed which really works well even with an old military radio, the B25. The tuner is as simple as it gets, an LC low pass filter. Simply “Plug and play!!!”. (The environment does have a slight effect though)

40m “Fixed tuned” end fed

          

A more conventional end fed arrangement uses a primary and secondary coil wound on a suitable toroid and capacitor where resonance on the secondary tuned circuit causes a high impedance at the resonant frequency thus adjusting for the relatively high input impedance at the end of the end fed dipole.

Manual End fed tuner

Then when I thought I’d started to understand end feds there came along multiband end feds with no tuning needed at all (After intial tuning of the lengths of the radiator). The section before the loading coil is a half wave wire on the SECOND band in this “multiband” antenna.

 

It requires building an impedance transformer. Here there is confusing information on how to build one but this is the best example I could find. What is important here is how to count the windings. Why the one half of the secondary coil is wound like this is still a guess? The primary winding twisted around the first two windings of the secondary is a must for best coupling, apparently.

The purpose of the 100 pF very high voltage capacitor across the primary winding is also a guess? It actually forms a parallel tuned circuit in the primary winding whose resonance is “X”. One thing that does happen apparently is they get blown up while using high power on the lowest band of the multiband end fed. They need to be able to handle HIGH VOLTAGE!!!

The 1:64 impedance transformer

I built my own miniature 1:64 imedance transformer using a T50-2 (I think) and a 100pF 1000v capacitor across the feedpoint.

Another good example ……….

 

And a good guidelind for impedance RATIO’s – Do the actual INDUCTANCES really matter? It’s the RATIOS that are important here.

Looking back at the windom antenna, could one not simply insert the secondary coil in line with the end fed dipole around .05 of a wavelength from the end? The .05 wavelength of wire has been suggested in many writings as a suitable length for a “counterpoise”.

There is no adjustable capacitor in the secondary here as used in the end fed tuners mentioned above and is surely simply feeding a dipole other than at the centre or a third of the way from the end as in the windom.

50 ohms transformed via the 1:64 impedance transformer to 3200 ohms (50 x 64) should give a reasonably good match  …… as far as a single band antenna is concerned. No tuning ……..

It does work ….. I’ve just got to get mine to work!!!

73 de Eddie ZS6BNE

 

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YouKits HB1A – Adjusting the battery level indication

The HB1A is an awesome little rig with many hidden secrets.

Mine was reading a little higher than the actual battery voltage I was using. While it was open, as it often is nowadays, I noticed a trimpot (UR1 Bat) more or less in the middle at the back of the PCB

 

Adjusting this trimpot, I was able to get the correct battery voltage indication on the LCD display.

The next mission – Power output issues need to be resolved ….

73 de Eddie ZS6BNE

YouKits HB1A – Replacing the LCD module

With my plans for minimalistic, CW only, RaDAR activities I managed to swop unused equipment for a YouKits HB1A 3 band (40m/30m/20m) QRP trail style radio but needed to give the LCD screen some attention. I considered this to be “bonding time” between myself and the rig. There is not much information on the Net so I decided to document the steps I took to do the replacement an operation that took a nerve racking four hours to do.

I needed to remove the back cover, the control knobs, the PCB retaining screws (2 of) , the nut and screw holding the power transistor in place for heat sinking and also the coax connector.

The module’s connector pins needed to be unsoldered (12 of them) but it was a mission and using a solder sucker didn’t help at all. This is generally a difficult operation as many of us will know.

I was hoping for a dry joint somewhere although the symptoms didn’t agree but I tried anyway as a first line repair without success.

I had to eventually use my Dremel drill with milling bit to cut the module away and use a sharp wire cutter to remove the left over PCB sections from the pins.

I had some coffee before continuing.

The pins needed to be cleaned before they could fit into the holes of the new LCD module. I also used a scribe to try and slightly increase the wire holes sizes on the LCD module thanks to a suggestion by my friend Daryl ZS6DLL. I soldered them lightly into place (Thinking of the next guy that may need to unsolder again one day!!!)

I was wary of applying power but things need to be done and I was relieved to see the new module worked!!!

Unfortunately, once all was reassembled the rig wasn’t putting out any power and not receiving any signals either. But, that’s for the next bonding phase. Fortunately this is a rig that can be repaired by yourself with a little patience and ingenuity, lots of patience!

I suspect (hoping) the problem lies in the vicinity of the BNC coax connector …. I’ll need to redo the PCB to connector connection using a short flylead.

SMD devices are so tiny but fortunately it wasn’t necessary to go to that level, not yet anyway.

UPDATE

The RX / TX problem was caused by a damaged L4 inductor that was damaged during the LCD replacement, a tiny scratch on the component.

If you zoom in on the picture you can see it. (Top left) I temporarily replaced it with a 1.1 uH inductor and the receiver was it’s awesome self again!

Hope someone finds this information helpful one day!

73 de Eddie ZS6BNE

RaDAR – Redundant radio equipment

For years now my focus has been RaDAR.

APRS and high power 2m FM communications was also high on the agenda but sadly not many people are active using such modes in my little town. Mostly limited to built up areas like Gauteng and Pretoria.

We did have a high activity rate using packet radio once, our club even ran two packet radio BBS’s! (ZS0LTG and ZS0TFK).

I bought an Alinco mobile rig, the DR135 a few years back and installed the optional built in Packet TNC. This enables the rig for APRS / Packet radio use and can be used to talk to the ISS too, not only on voice but using the AX25 digital modes! The rig has also been configured (Link) for monitoring the AM aircraft band, receive only.

So this rig sits unused in my shack, it would be great if I could swop it for an HB1A QRP rig or some similar QRP gear. That’s more down my alley.

Here in South Africa we’re working on a CW proficiency badge system to promote the learning and use of CW as an adventure activity like RaDAR, SOTA and POTA

73 de Eddie ZS6BNE

 

RaDAR – Flag wars

My grandson (11) and I (58) developed this awesome game this weekend. Lots of fun and good RaDAR physical training too! Next to our little house “down by the burning river” we have a four hectare area with rocks and many bushes.

Flag Wars

by

Eddie and Eduan Leighton

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Requirements:

Own water and backpack.

Protective headgear or cap.

Sun protection.

Trail shoes.

A general recce to be done by all competitors before the games begin.

Experience needed:

Danger awareness.

Trail running.

General fitness.

Possible dangers:

Twisting an ankle

Flesh wounds caused by thorn bushes / trees.

Unseen holes

Tripping over rocks

Snake bites but the chances are very minimal (it needs to be mentioned).

Rules:

Each competitor places his flag pole on his side of the “operational area”.

A call is made to start the game.

Each competitor moves out to find the other’s flag trying not to be seen.

On finding the opponent’s flag, move back to your flag (Hopefully knowing where it is!).

Once back home with the opponents flag, you have immunity and thus win the game.

If you are caught by the opponent while carrying the opponent’s flag you are taken prisoner and the opponent wins the game.

Experiencing the game:

My route back to “camp” running back with Eduan’s flag. He saw me and gave chase, pretty fast kid I know, and he was close on my heels! I jumped the rocks entering the “desert area”, swung left and bolted for my flag hidden among the bushes, seconds from being “caught” and held “prisoner” and losing the game.

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In desperation to get away from him I ran through thorn bushes, the same just touching his forehead. Next time he must wear a cap, at least.

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Eduan won the first round, he sneaked back with my flag before I even found his!  He can also track you, quietly without being seen! He’s a natural!

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He said, it’s the best game he’d ever played against his granddad!!!

RaDAR – A little history from way back then

I was asked to write a CV of my amateur radio career in less than 500 words so here goes, I hope I can remember the important details! Maybe I should write it as “the third person”.

…..

Eddie Leighton took interest in amateur radio way back in 1974 and, after many weekly night classes, wrote the November written technical and regulation RAE. Morse code was required for an unrestricted ZS licence and, although largely self taught, Eddie managed to pass the 12 w.p.m. test. Eddie was issued with the call sign ZS6BNE in February 1975. He was still in high school until he matriculated at the end of 1976.

Eddie was called up to do national service in 1977. It was not until basic training was completed was he transferred to Wits command signal unit in the middle of 1977 where he spent another 18 months as a signaller also manning the Hamnet military station ZS6VT. On clearing out at the end of 1978 Eddie joined the Post Office as a pupil telecommunications technician. He was married in 1980.

Eddie was for many years the chairman for the Lichtenburg amateur radio club. On a few occasions he presented the RAE and morse classes in Lichtenburg where he stayed. When his own son was old enough he also became a ham and was issued with the call sign ZU6AAI. Eddie spent many hours in the “shack” with his son which proved quite beneficial in later years.

From the year 2000 Eddie actively wrote articles for the SARL’s publication, Radio ZS. This included general stories and later articles on digital modes, satellite communications and Rapid Deployment Amateur Radio.

Since attending the first “Radio technology in action” presentations of the SARL, Eddie decided to give something back in the form of touring South Africa firstly giving satellite communications presentations and the following year presentations on RaDAR which has become his passion from the year 2007 till now.

In 2010, Eddie earned the radio amateur of the year award.This award recognises someone who has made a major contribution to promoting activities and technical excellence. Eddie received the award on two counts. He promotes amateur radio satellite operation through articles in the South African Radio League’s publication Radio ZS. His second project is the development of Rapid Deployment of Amateur Radio (RaDAR).

RaDAR was recently presented and accepted at the IARU region 1 meeting. Eddie continues to promote amateur radio and especially the rather unusual concept of RaDAR in the form of short promotional video content and Blogs. He is in constant contact with interested hams via the various social media.

 

RaDAR – My RaDAR Playground history

What a harsh reminder of early beginnings, these pictures I discovered here. Fond memories actually …..

Molopo 50

I dreamed I could do it all myself!

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Fortunately there were contractors willing to help!

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Foundations were dug

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and filled with reinforced concrete designed to take the load of a double height building.

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A deep hole was dug amongst the natural rock.

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It would become a french drain serving two households.

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with a second compartment for soapy water drainage,

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Then floor height walls were built on the foundations and filled with gravel.

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and time to lay the underground electrical conduits ….

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Section for section the concrete slabs were laid.

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Until the floor was complete, a rough finish.

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and so it stood this way ….. for a very long time.

We planted trees, in the meantime.