RaDAR – The end fed tuner dilemma

The following was quite sufficient for my understanding of end feds and worked well for me, but how well?

This tuner supposedly works for 40m right up to 15m. It uses a T50-2 toroid wound with 24 turns on the scondary, link coupled with 3 turns on the primary. An impedance transformer.

Here’s an interesting interpretation. The impedance transformation ratio is important here. Our transformer info lies at the bottom of the list …. an impedance ratio of 1:64.

So for 50 ohms on the primary where the rig is connected, we’d expect to see 3200 ohms on the secondary where the tuned circuit resides. Now that sounds more like an end fed’s feedpoint impedance! The circuit on the secondary also looks more like this.

The impedance at resonance is high, typically similar to that of the end fed!

So, this was my original understanding of an end fed tuner from the beginning. It made “no difference” what the inductance / capacitance ratios were as long as you have a resonant circuit to which the end fed was connected …..

The impedance transformation ratio is not always a hundred percent predictable which made the Fuchs tuner popular. It was also the first end fed tuner I built. Variable ratios, variable inductance and capacitance for the parallel tuned circuit on the secondary!

So why use a simple “L Match” with the complexity and requirements for suitable inductances (and switching) per impedance when you can simply use a link coupled parallel tuned circuit (Impedance transformer) capable of resonance at the required frequencies?

That is the question ……. ?

An interesting comment I found on eham.net written by Dale Hunt, “Notice, however, that the number of turns does NOT depend on the operating frequency!  The capacitor has to be able to tune the secondary to resonance (taking into account any stray reactance).  A variable capacitor with a 9 : 1 capacitance range will cover a 3 : 1 frequency range, so if the coil inductance is chosen carefully a single variable will cover all three bands.  20m near the minimum, 40m near the  maximum, and 30m in the middle somewhere.  For any specific capacitance range, you can calculate the desired inductance to tune the necessary range.  In your case, 10 to 100pf with 10uH will tune 5 to 16 MHz. 10uH requires about 45 turns on a T-50-2 core.  If you use a 5 turn primary that gives a 9 : 1 turns ratio.  You can vary the number of turns to see what gives the better match with the specific wires and capacitor you are using (and any stray circuit capacitance, which will reduce the tuning range.) “.

Ideal for the HB1A!!!

So, then a 10uH inductor wound on a T80-2 toroid will need 43 turns (103 cm of wire) and the following capacitance values / band.

40m – 50 pF

30m – 25 pF

20m – 13 pF

 

73 de Eddie ZS6BNE

 

 

RaDAR – Assessing the QRO kit

A little while ago I swapped my FT-847 (Satellite capable HF/VHF/UHF radio) + FC-30 automatic ATU for an FT-897d (HF/VHF/UHF radio) plus accessories which included a LDG AT-897 automatic ATU, Collins SSB and CW filters and a mobile bracket (Unable to use with fitted ATU).

I did have the TOKO filter replacement done by Daniel, ZS6JR which cost me just over a grand but good to know the rig is sound and in optimum working condition.

I later bought a second hand built in FP-30 AC power supply for it. It wasn’t cheap either but I felt it was a useful addition for “Fixed station RaDAR” without having the need to transport a separate high power (20A Plus)13.8 volt DC power supply.

The rig can take internal batteries or a battery supply can be plugged in using a separate DC cable. 7 A / Hr SLABS work well in this regard. All this fits in well for RaDAR

I did some price checks with values I got off the Internet.

FT-897d – $725, AT-897 – $165, FP-30 – $175 and MMB-50 – $37 = $1,102 = R14,320.00

That’s a pretty price to pay for a rig with it’s accessories but sounds more or less what it is. A good investment. I keep it within a protective carrying case for safe keeping.

 

73 de Eddie ZS6BNE

RaDAR – Deploying the 160m end fed half wave antenna

You need good height and preferably vertical polarization if you wish to work DX on the top band. Well that is quite possibly true but what we did here, with a relatively ineffective antenna, didn’t make the fun any less. It worked! Don’t be deterred by the “impossibilities” we sometimes encounter in our ham lives …..

From a previous post on modifying the MFJ945e ATU to that of an end fed tuner, after many strange results I stripped the wafer switch from the equation and also found one of the capacitor plates shorting during rotation. It was evident while looking at the signal on an oscilloscope and finding the signal dissapear while tuning! The ATU was second hand with an unknown usage history so difficult to say whether damage occurred some time during it’s life.

The 32 uH inductor wound on a T157-2 toroid wired directly without any switching (Besides the ATU bypass switch)

The variable capacitors wired in parallel to give a maximum of 200 + 200 = 400 pF

I bought a roll of a 100 meters of 1.5 mm pvc covered copper wire usually used for house wiring of lighting circuits. The idea was to unroll the wire without kinks and tangles in the veld! Young Eduan, my grandson, and I took on the challenge in my “RaDAR playground”. It eventually became fun for him and he wanted to take part in all the deployment activities including the roll of RaDAR photographer!

We used the trees and bushes as supports for the wire, using a rock and throwing the wire over them as we progressed towards our home around two hundred meters away.

Some trees or bushes were bigger than others and not necessarily in line with one another but we zig zagged between them, the sole purpose of getting the wire off the ground through it’s entire length. Darkness was setting in, we had to move fast!

We eventually got home but there was no time to go back and I had to be happy with the hope that most of the wire was hanging between the trees!

The calculated length of the 160m half wave end fed was 79.5 meters so I measured 20 meters of wire while reeling it in and cut it off hoping that the total wire length was actually close to 100 meters long as advertised on the label! I connected up the FT-897 and modified ATU and the best I could get was around 2:1 SWR with a slight dip when tuning the capacitors but the capacity was not much and should have been around 200 or so picofarads ….

I called on 160m, Johann ZS4DZ heard me but could not hear what I was saying but through many retries we completed the QSO. Lukas ZS6LH just made out what I was saying, my audio was so distorted. I thought RF was possibly the culprit and then I did something which I don’t normally do running end feds on 40m and higher. I used the 20 meter piece of wire which I cut off as a counterpoise off the GND terminal of the ATU and just laid it on the ground, walking around the building. I could then get around 1.1:1 SWR on the ATU’s meter and that of the rig and then I was getting clear reports of 59+20 and the evening was still young as far as NVIS propagation was concerned!

I came back a little later and there was Ed ZS6UT, he was pushing my S Meter further to the right than I had ever seen …. is that 59 + 60dB ??? There’s around 300 km between us.

I wasn’t really part of the top band contest as such but I could give a contact to four participants before packing up. Unfortunately no CW yet there were CW capable operators on the band.

I went back yesterday (Sunday) afternoon to tie down the end point for use on another weekend. I found it lying on the ground and one or two places where the wire was sagging between the trees which probably accounted for the low capacity settings on the ATU!

The wire is tied down nicely now and nicely tensioned too. Possibly the 160m end fed wire could be used for the higher bands. It’s pointing NNW so it could be a good “end fire” system for DX on 40m or 20m !!! The next test phase …..

As always, it was fun. And I learnt that a counterpoise IS required, however small but it IS REQUIRED if only a SINGLE wire lying on the ground!

73 de Eddie ZS6BNE

 

 

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.

In the likely event of using the T157-2 Toroid then the winding information is as such :

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