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80 Meter Coil
Common Mode Choke
I was actually surprised how quickly and easy was the installation with Mark III EHU. The Mark I and II EHUs require an additional internal modification described in the manual. I have prepared the control line at the time of the antenna installation so it took me about 30 minutes to install the coil. |
The process is very simple and straightforward:
1. Mount the coil on the EHU – with the Mark III EHU it requires a couple of screws to be removed from the EHU enclosure and replaced with the supplied longer screws and plastic spacers.
2. Disconnect the radial field from the EHU and connect it to the ground screw of the coil.
3. Disconnect the feedline from the EHU and connect it to the coil.
4. Connect the output of the coil to the RF connector of the EHU.
5. Connect the contol line to coil.
6. Enable the coil in the antenna controller.
I also received new version firmware, which I installed with the help of the supplied chip-extractor tool.
After installation of the coil, I had to do Create/Modify and re-adjust the length of antenna element for each band and the 80m sub-bands (for each coil tap). The extra loading and electrical length of the wires from the added coil caused my SWR to go up a little bit from before, even after the element length correction on bands where the coil is normally in by-pass mode. It is more noticeable on 20 meters - the SWR went from 1.1:1 to almost 1.3:1. The SWR on 80 meters with my radial system ( I have some radials longer than 70 feet) is quite low – 1.1:1 – 1.2:1 but the bandwidth is narrow and I have to move the frequency in antenna controller often when I move the radio’s frequency to keep the SWR low. As predicted by SteppIR on 15, 12 and 10 meters the SWR is lower in ¾ wavelength than in ¼ mode and the antenna works better in ¾ mode. Overall, the SWR is low on all HF amateur bands with maximum of 1.5:1 on 10 meters in ¼ wavelength mode. I have not tested the antenna on 6 meters. As expected, signal strength is good in receive and I can’t see a difference between the BigIR and my 40 feet high full size G5RV in A/B test on the lower bands. On transmit I was able to make many good DX contacts on 80 meters with 5/9 reports. The low radiation angle is a very good thing for DX but as expected I had difficulties contacting stations too close to me.
I am happy with the coil and I think that it is worth getting it for the extra band coverage. It works as expected with no surprises and no ill effects on the antenna. The slightly higher SWR with the coil is not really a concern for me – it is still within the BigIR’s specs for SWR < 1.5:1. I am planning to put another 20 radials (currently I have 40).
It is not a perfect product by any means but it is pretty good and most of the “issues” I have with the coil can be fixed by simple modifications and none are “show stoppers” IMHO.
- The biggest issue that I have with the coil is the SteppIR’s choice of brass terminal screws for the control line. Exposed terminals instead of a weatherproof connector as the one on the EHU is not something that I am fond of. This is a bad design decision! It is cheaper and easier to manufacture the coil by soldering screws straight to the PCB but I do not think it is a very smart choice for electronic equipment that is exposed to the elements! SteppIR recommends the use of RTV silicone to protect the terminal screws but this is messy, looks unprofessional and makes the disconnection of the cable difficult. A 4-pin weather-resistant connector as the one on the EHU would have been a better choice and there is plenty of room to install it too. Such type of connector is very easy to protect with self-fusing silicone tape as well. The exposed brass screws and lugs are prone to oxidation if left unprotected. The constant electric current, dissimilar metals and moisture is recipe for corrosion. The accumulation of snow and ice on the terminal screws is another thing to worry about. The stepper motor driver chips are un-protected to short and should such an event occur on the screws, it will damage the drivers. With the exposed terminal screws the risk for short is higher than with an insulated and sealed connector. I might try to modify it and install good connector. Meanwhile see my “less-than-a-dollar” snow/ice guard.
- The design of the “Roto Switch”. Unfortunately, the 80m coil is an after-thought so SteppIR decided to utilize the ability of the antenna controller to control stepper motors and they designed the Roto-Switch around it. It would have been much better to use a ceramic rotary switch with rotary solenoid but this approach requires different type of control signals, not available in the current antenna controller. Their “Roto Switch” is designed with PCB static contacts. I am not sure for how many cycles SteppIR tested the switch but we are talking here about metal-on-metal friction with no lubrication. Furthermore, the foil on the PCB is very thin and the rotating metal contact points will leave their mark of wear– after certain number of cycles, the thin gold plating will be gone from the PCB and next is the copper foil. Repair of worn off static contacts requires replacement of the PCB – a costly repair. Any arcing in the switch will damage the thin copper foil instantly! I could not find any information about the number of cycles they guarantee on the switch. I will be doing coil maintenance once a year and I’ll be using Caig Labs DeoxIt Power Booster and Pro Gold spray for contact cleaning and lubrication. Fortunately, the coil enclosure is completely sealed so no dust can get in stick on the switch and the lubrication film from ProGold is very thin.
- Manufacturing dust in the enclosure! When I opened up the coil enclosure I discovered a lot of dust and fiberglass debris left over from the manufacturing process. Compressed air took care of it but that’s something they should do at the factory!
- Output pigtail! The output cable goes thru a slightly larger hole in the enclosure without anything seal it - just two cable ties – one on each side of the wall, providing some stress relief. The cable tie inside was very loose and every time I pull on the cable (very gently), the cable will come out more and more. The loop of the loose cable tie inside was sliding over the cable letting it go. Lack of proper seal will allow also moist air to come inside and condense. I used two pieces of self-fusing silicone tape – one on each side of the cable. I formed tight O-rings /sleeves and reinforced them with new cable ties over the silicone tape. First, I installed the inside seal, than very tightly I wrapped the tape around the cable on the outside, making sure that it seals well the opening around the cable. Now the stress relief on the cable is better and I have an airtight seal around the cable at the exiting point.
- Stiff blue wires! The two blue wires (see the pictures) going to the rotating arm of the Roto-switch are way too stiff. They have used stranded, heavy gauge wire but with too few stands and those blue wires are very stiff. As a result from this, when power is removed from the controller, the stepper motor will loose holding power and the wires will act as springs, pushing (pulling) the contact arm from it’s current position to some unknown position (based on the way the wires were soldered and bended). The arm will stop somewhere between the switch positions (Murphy’s Law) and this will interrupt the signal path. In other words - If power is lost, the antenna will be lost even if it is already extended. That’s bad! During an emergency, when the power goes out I rather have the antenna stuck on a single band than having no antenna. I should replace those wires with more flexible ones, with less “spring action”. In addition I’ll attach (glue?) the terminal block between the blue wire and the output pigtail to the PCB (or the enclosure) as to provide a fixed end point for the wire. Ideally, the rotating arm should stay where it is left even with no power.
- Coil tap points. The enamel of the coil wire is removed (scratched off) from the spots under the tap point but the wire is not tinned there – just left as bare copper. They should have tinned the wire to protect it from corrosion and to maintain good electrical contact. A minor touch indeed but at least I would not see dark or green oxidized copper next time I open the enclosure. I used a little bit of DeoxIt Power Booster D5 at the tap point-wire junctions. Probably some heavy dielectric grease will work fine too. This will protect the connections from any moisture and will slow down the oxidation. Tinning the wire there is best but it is not possible without undoing the coil – something I am not inclined to do.
- The manual of the antenna is still very poor - almost a year after I bought the BigIR there is no improvement whatsoever! The coil manual is a little better but not by much. SteppIR should re-write those manuals!!! There is simply no excuse for such poor job on the manuals! The user manual is just awful!! There is very little in there about the vertical. Still no good firmware history document. The new firmware fixed some issues with the ¾ mode but I had to dig into the reflector to find out what it did.
- Self-adhesive, rubber “coil winding separators”! I am not sure that during the summer when the temperature in the coil enclosure gets very high if the glue on those self-adhesive separator pads will still work or I’ll find them all over the enclosure. It seemed that those things were coming off from the coil form already. I had to press them back in place. Not a big deal – I can always re-glue them with better glue.
- Grounding of the RF connector. The ground connection between the RF input connector and the PCB board is provided by only one (!) very small screw! The connector has 4 screw holes (so as the PCB) – two of them (diagonally) are used to mechanically attach the RF connector and the whole PCB assembly to the plastic coil enclosure. Those two screws are not reliable ground connection because the heads of the screws are not touching the connector (the plastic enclosure wall and the rubber gasket are between the screw heads and the connector-PCB “sandwich”). The PCB has 2 more holes for ground screws but in my coil only one screw was installed. The small screw is the only connection between the outside shell of the RF connector and the ground copper on the PCB (where the radial system is connected). There is no excuse for not using the other screw aside from saving on labor and on the actual screw (!?). I had to drill carefully a countersink in the other RF connector hole (the screw head must be flush with the connector’s front because the connector is pressed against the rubber gasket and the inside plastic wall). I used small stainless countersink screw, a washer, lock-washer and stainless steel nut to tighten the connector to the PCB and improve the ground. Good ground connection between the coax feed line and the antenna’s radial system is essential and two screws are better than one!
An idea to experiment with: How about a version of the antenna with the 80 meter coil UNDER the EHU? The antenna’s EHU can be installed on a longer post, higher from the ground and the coil can be installed under the EHU, horizontally, in a classic loaded vertical configuration. I am not sure what will be the benefit from this – the signal will travel in almost perfect vertical path and it might lead to better SWR in ¼ mode. If one day I find the time, I might try this. I will have to fabricate some sort of a post extension and some mounting brackets for the coil. I might even move the output of the coil to the “top” side of the enclosure after it is turned horizontally (so the coil is straight).