RaDAR – An end fed for 160m

It’s been many, many years since I’ve last had a QSO on 160m and I believe there is a four day local contest taking place this weekend which has already started.

While on the subject of end feds, I thought I’d use my new found tools to design such an end fed. Firstly, using the spreadsheet created by Pierre, ZS6A. L network ATU calculation

The length of wire needed for a half wave end fed. At least two rolls of flex wire from the hardware store!

Then suitable inductor and capacitance values for an LC network taking the feedpoint impedance at 2,800 ohms (As with the ZS6U Minishack Special tuner design).

I have a few T80-2 toroids in the parts box so I used the “Mini ring core calculator” program to determine the number of windings required for a 32uH inductor. Thanks to Daryl, ZS6DLL for the link to this awesome program! (It works on Linux too, under Wine). Maybe / Hopefully this will work in the MFJ box!!! I’ll be running MAXIMUM 100W.

 

It may just be worth my while setting up for 160m. I should be in my RaDAR playground on Saturday afternoon where there is plenty of space for an 80 meter long wire. I’ll take the 897d along plus the usual SLABS (And the charger).

And of course that rebellious MFJ 945e box!!!

 

73 de Eddie ZS6BNE

 

RaDAR – A scientific approach to EFHWA tuners

I was browsing the antenna section of an old ham radio book this morning and the LC tuner configurations were quite prominent. In all cases the tuners consisted of a tapped inductor and a capacitor to ground on the antenna side which is a well known configuration for tuning long wire antennas. A good earth requirement was often mentioned.

The past couple of years the end fed has become popular with me specifically because a good earth is NOT a requirement and fits in well with RaDAR which operates far away from anything close to a perfect world! However, delving deeper and deeper into the complex world of end fed antennas a strive for near perfection appears to be valid.

In that old book I read this morning, mention was made of using a neon tube to indicate maximum brightness when tuning the tuner. This is nothing other than ensuring MAXIMUM POWER TRANSFER through proper matching of the rig’s 50 ohm impedance to the variable high impedances of the long wire antenna and this will be the topic of discussion here.

My goal is to build an antenna tuner similar to that designed by the late Colin Dickman, ZS6U and is well known as the “ZS6U Minishack special”. His tuner uses a coil of specific dimensions and I want to do much the same but using a toroid. The antenna is a 21.03m length of wire which can be used for 40m, 20m, 15m and 10m.

Colin’s calculated optimum values of inductance and capacitance values for the LC tuner for the various frequencies and feedpoint impedances of the 21.03m length of wire.

The toroid I have in my parts box and the same one used for my recent 20m end fed experiment appears to be a T130-2. It’s dimensions are as follows.

In order to achieve the same inductances calculated by Colin, I used an online calculator to determine the windings required for a certain inductance on this specific toroid. The windings can be tapped and taken to a suitable selector switch.

I’ll be using my modified MFJ945e tuner keeping only the SWR meter circuitry but removing all the other coils and replacing them with this configuration.

40 Meters

20 Meters

15 Meters

10 Meters 

Well now, proof of the pudding is in the eating. I’ll build the tuner tonight and hopefully I should have a tuner that can be used for these bands using a single, relatively short, wire – An end fed!!!

Update

To double check without a guess I measured the size of my unknown toroid and it was larger than I thought and appears to be a T157-2 (Red)

The site I was using for turns calulations was somehow no longer operational so I used http://toroids.info/T157-2.php 

40 Meters

20 Meters

15 Meters

10 Meters

Update 2017-06-22

Last night I wound the coil on the “T157-2” toroid according to the above online calculations using a hand drawn diagram as a guideline.

and wired it into the old MFJ945e tuner housing. Tonight may see an on air test using the FT-817ND, my rig of choice.

 

 

73 de Eddie ZS6BNE

 

 

 

RaDAR – Reducing pack weight

The are many miniature QRP shortwave ham radios available on the market but few come close to the FT-817ND or the KX3 for size, weight, versatility and RELIABILITY!

I recently aquired a You Kits HB1A which needed a few repairs (Good bonding time) and one would think that with such a rig the pack weight / size can be radically reduced. Not so! The same antenna / antenna logistics like ropes, poles and tent pegs need to be carried. Then you need to carry a key, I carry the same key. I carry a mic …. with the 817 at least and then you have SSB functionality too which is a must because of the very sparsely populated group of ZS CW operators! Your chances are 90 percent higher in having a successful QSO on SSB in ZS.

Then it’s a battery – I use rechargeable penlights and maybe a 7 A/Hr SLAB or two which in my opinion are the most reliable but yes, heavyish. The weight and size difference between the HB1A and the 817 isn’t all that much. For the versatility of the 817 I’d add that small extra weight / size difference with pleasure. You may need to carry a GPS or cell / smartphone and maybe a spare battery or two for them too. The rest of the pack contains support items like a headlamp, insect repellant, small tools, water, layers of clothing (Not forgetting a raincoat) and maybe a few snacks suitable for the hike / jog distance.

So really the choice of rig has little difference on the overall pack weight unless you take an absolute minimalistic approach to the communications kit keeping in mind how far can one communicate with such a rig, supported modes by which I mean human operators on the other side with whom you need to communicate.

Power supply recharging is an absoute must for multi day hikes. You can’t afford to be left without power for then the total communications kit will mean nothing. A roll op solar charging system will need to become part of the kit.

Nothing has been said about shelter and sleeping facilities like a good sleeping bag. That can be lightweight but overall mass becomes larger with each extra item.

RaDAR allows one to practice using various considerations in the real world. Practice makes perfect!

73 de Eddie ZS6BNE

 

RaDAR – R2R Attempt with Tom G0SBW

This past weekend I tried to have a RaDAR to RaDAR (R2R) QSO with Tom G0SBW. I did some tests first on the Friday evening using my newly built 20m end fed driving it with my battery powered FT-897d

My friend Roger, ex ZS6RJ now M0ORD was on the other side. He was  using a multiband end fed and running 400W. Conditions were not good but I did manage to work Andrey UB3A with pretty good signal reports both ways. Just in time before someone switched something on and I had 59 QRM!

That proved to me that my antenna was at least working. I did however have to limit my power to 80W to prevent flashovers on the tuning capacitor of the end fed. Not serious ….

All of us had communications via WhatsApp to arrange skeds, frequencies and times but if propagation isn’t suitable then no radio communications are possible!

Tom and I tried on the Saturday evening. I went down to the river hoping to be free from any possible QRM. I found the end fed’s SWR in this location a little high and I needed to modify a small penknife as a trimming tool for the capacitor. I got a few RF burns on my fingers in the process but a ham has to do what a ham has to do!

Communications with Tom were not possible. There was also the AA CW Contest taking place with little space in which to call CQ but Roger found one and we tried to make contact. I did hear him faintly around 419. He was running 400W which proved that powers any lower would simply not work.

There was a friendly Russian station taking part in the AA Contest but he replied to my call and gave me a report anyway. He was Vasily UA1AFT. So for the weekend I had two good reports on the antenna and a RBN spot from OH6BG in Finland (My friend Julian OH8STN would love to hear this!), a whole 14 dB’s!!! That proved beyond any doubt that the antenna was working well and if conditions were right I could “Work the world” with this antenna!

Somehow my friend Pierre ZS6A just 250km east of me found 20m to be rather quiet which was quite strange. Possibly the end fed held vertical with the 10m fibreglass mast is the perfect antenna orientation for DX.

I had to work in the dark down by the river but at least that was good practice for RaDAR and of course new things were learnt and new ideas generated.

The 15th of July will see the second 2017 RaDAR Challenge. As always, it’s going to be challenging but always FUN!!!

73 de Eddie ZS6BNE

RaDAR – Fixed tuned end feds

There is no doubt, end feds work!

Whether no-tune, multiband, end feds work is still debateable (In my opinion).

Last night I built a 20m end fed in particular to attempt a RaDAR to RaDAR QSO with Tom G0SBW on the weekend.

On receive, I have found when the best signal strength is where the capacitor plates are unmeshed then you’re no where near resonance on the LC low pass filter tuned circuit. I pulled this toroid out of a MFJ945e mobile tuner which I am modifying as a Fuchs style tuner and have no idea of the type but it is a red toroid which obviously should be suitable.

I started off with 26 windings and ended up at around 13 and found resonance with the capacitor half meshed. With a SWR meter in line I came close to zero SWR and using the FT-817’s built in SWR indicator it was confirmed! Full power output from the 817.

Looking forward to using my 10m fibreglass telescopic mast, this end fed (10.1m wire) and my battery powered (7 A/Hr SLABS) FT-897d to make contact with Tom. He recently had a QSO with Namibia so conditions may be favourable!

The 20m end fed circuit is very simple, I have a 40m end fed too which has proved itself over and over again!.

73 de Eddie ZS6BNE

 

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