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
4. Connect the output of the coil to the RF connector of
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
- 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
- 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).