Renovating my Amateur Radio Aerials Understanding the problem...
When we moved to Kemptown in Brighton in 1983 it was from a house much higher
up the Race Hill that dominates the eastern end of the town. Hence what was
once the reason I could hear and be heard for a long way on VHF was now a
impediment to my signal. However family came before radio and with two small
children the new house, for all its needs for repairs and redecoration, was a
good move. I'm still happily here.
I brought all the radio gear along hoping to make the best of the new
situation. That included my in-the-roof mounted aerial rotator that fed through
the tiles with a sleeve purpose made for me by a good friend Brian (G8BTC).
Brian even modified the sleeve when I moved to Kemptown to accommodate my new,
slightly narrower roof timbers. So I found a suitable spot, slid back a tile
and fitted it.
However it wasn't to be. A poor signal coupled with new jobs and new
responsibilities progressively moved me away from ham radio and into home
computers long before there was such a thing as a 'home computer' and so here I
am, nearly forty years later, a widower with the children now moved away and
with their own families and I want to get back into this ham radio lark again.
The problem with radios is that they need aerials.
The whole aerial business is further complicated by the fact that in the
intervening years the Morse test requirement for a 'full' license has been
removed and my G8 callsign is now a full license. I bought some rather vintage
HF gear and I wanted to use it. However HF, aka shortwave, aerials are even
bigger than my old VHF ones.
So let's get started...
A few years ago I had a 'TV' aerial rigger put up a 6/2/70 vertical whip for me
with a standard chimney lashing kit and a pole and that started my
rehabilitation onto VHF but now I wanted to get serious.
I had long since taken down the old VHF aerials on the rotator as they had
rusted out so all I had left was a pole with a rotator on the bottom going
through the old sleeve through the roof.
So Test it!
I hitched the rotator controller back onto the cable and powered up: It doesn't
seem to go round although I can find the null point where the controller stops
asking for power so the basic system is working... Bother. Must be the motor
unit. Admittedly it does look pretty sad with decades of deposits on
it.
So I unbolted the aerial mast from the driver unit and slipped it out. All that
white stuff seemed to be just calcification deposits. Good. Ominously the mast
didn't drop when I pulled the motor clear.
I took the drive unit down to the workshop and hooked it up to the controller
directly and it all worked just fine. All it wanted was a vigorous external
wire brushing to be lovely again. I wasn't sure if that was good news or bad
news as just having to buy a new rotator unit would have been far more
simple.
After much heaving, oiling, banging, threats and entreaties I had to admit the
mast was now irrevocably bonded to the sleeve. This was going to be a far more
major rebuild than I had anticipated. Finally, fuelled more by rage than logic,
I sawed off the mast above and below the sleeve, demounted it and took it down
to the workshop for some serious brutality.
Nothing, absolutely nothing, impressed it. I finally used an angle grinder to
cut the sleeve away from the body of the mounting and started to plan a new
fitting.
Fixing the problem...
A web search showed a rather nice Yaesu bearing for masts going through things,
the Yaesu GS-050 Thrust Bearing. So a new piece of steel pipe to be the
new sleeve was ordered and also a replacement mast that was both thin enough to
have clearance on the sleeve so there is no tight metal on metal contact to
corrode into a lump and also that was the right size to match the bearing.
Then there was, however, the problem that the bearing was designed to mount on
a plate not on the end of a tube.
So I need a plate to go on the top of my new sleeve:
It's machining time! I want round and I have a lathe. They do round as their
whole raison d'etre.
I sawed out a square plate, drilled the bolt holes, then used the lathe to cut
the big hole in the middle and then take off the pointy corners. I think it's
come out rather well.
Yaesu has placed the bolts, you will notice, rather close to the edge of the
central hole and, as the sleeve inside diameter is a precise fit for the hole
and the sleeve wall is 3mm, I need spaces for the bolt heads to go in before I
welded it into place.
Dremel time!
That little hand held battery powered toy, I have the 8200, never ceases to
amaze me with what it does for me. Especially with a parting off disk on
it.
Then weld it up, not my prettiest work but functional, a heavy wire brushing,
slap on the anti-rust treatment and then some paint.
Brian's old frame, now with a new sleeve, was ready to go back in the roof.
I power sanded the mounting space between two rafters so it went in in a
controlled fashion. I seem to remember, all those decades ago, loosing my
temper and doing some percussive alignment. This time it was trued up against a
spirit level and then tightened.
And finally I put it all out through the roof.
I will admit that grasping a 3 meter mast by the bottom and trying to feed it
vertically into a hole I could not see was fun but it was a calm day and it
went in OK.
Add some aerials
As I have said I didn't have any aerials to go back up and I didn't feel like
buying a big butch VHF array yet so I Amazoned a cheapish 2m/70cm short Yagi
and an HF vertical.
The HF whip may have been a slight error of judgement. It is the SIGMA
EUROCOM SE-HF-X80 and it gets good reviews but it's a lot bigger in real
life than I imagined. Six meters is very tall in a domestic environment and
watching it wag in the wind is, um, educational. However it tunes well on the
ATU and pulls in a lot of good stuff. It's on the rotator mast because I wanted
it in the middle of the house to help with current 'safety' rules so I have an
omnidirectional vertical that I can rotate. <sigh>
The Ailunce AY04 Dual Band Yagi tucks up under it and is re-drilled for
horizontal mounting. I checked it on the VNA for a good 50Ω match before
tightening things up. I had a slight incident testing when I had it at the
bottom of the mast to adjust and carelessly slammed the skylight window on it
and had to replace one of the elements before I even started. However it's made
of standard 'off the shelf' tube so a pretty straightforward fix. I didn't
fancy getting a big butch Yagi yet as they need you to know exactly where to
point them to get the advantages of all that gain and for VHF my 'clear' arc
only stretches from about Dieppe to Cherbourg and that's pretending the
buildings to the south of me will kindly duck.
I also bought a commercial, ready made, trapped, end fed long wire, the
Vibroplex EF-80-10-JR-KW. This was to replace the Ebay sourced
G5RV that itself replaced two sequential Carolina Windoms. These
were sadly never much good as they were too low, too close to things at the
ends and made of cheap parts. Also the cable I had used to hook them up had
leaked rainwater and was now really only scrap. The new system is tethered to
the chimney stack lashing I have for the VHF vertical with seafaring boat
fittings. It is fed into the house at the roof level and is 26 meters long so
it reaches well down my garden to where I have placed a 7.3 meter high pole
attached to the end of the falconry mewes with a pully block at the top. This
keeps it well away from people to help comply with modern 'safety' practices
(yes I did do all the sums and then saved the PDFs from the RSGB's calculator
for full legal power). It feeds in through the roof and then through a ferrite
shell balancer, aka a choke balun. It tunes up well and as a first test I
worked Italy on 20 meters with good reports both ways and some nice comments on
the old FT101ZD's audio.
Inside the roof all the feeders go through my home-made water traps (two back
to back sockets separated by M3 bolts to give a horizontal air gap) and ensure
that the ever so hard to replace big fat feeders running down through the house
to the office are protected from that nasty wet stuff.
My preferred HF aerial tuning method is to first load up the transmitter on the
intended band into my big 1K5W 50Ω dummy load and then switch the aerial
of choice into the VNA network analyser, pre-calibrated and scanning the whole
sub-band required. Then trim the ATU for a good 50Ω resistive match over
the whole band. With a roller-coaster inductor ATU (MFJ-962D) and a
'live' Smith chart display this is all too easy. Then click two switches to
connect the transmitter onto the aerial and always completely unplug the VNA as
I fear that even letting it be near the linear could be a terminal experience.
With that I'm on the air. Am I the only one to think that tuning up in band on
full power is just plain rude?
Along the way I needed to waterproof things, this is 'Sussex by the sea' after
all. I capped the mast with a deep plug and worked down from there. It started
with good ol' duck tape but I had some roof work pending and a lead worker with
a flame torch that looked very acetylene blue (I should have asked) fabricated
me a custom 'chimney'. It's actually rather pretty. The gap round the mast
where it goes through the bearing then has a piece of twisted up tape down
inside it which is topped off with an outside grade filler and finally a ring
of roofing aluminium-tape.
However... That doesn't address the problem that when it is blowing an easterly
gale, not so uncommon on the English Channel coast, it blows the rain back up
under the tiles and I am reliant on the felting to stop it getting into the
house. I wanted to tape and sealant the felting to the pole but that lovely
lead 'chimney' is tight on the sleeve and to lift it off I will have to
dismantle a whole lot of aerials over a few theoretical drops of water running
down the outside of the sleeve... I just need a trap to catch it. So I sketch
out some ideas, fire up the openSCAD solid modelling software and 3D print a
part to do the job. It's not complicated. In fact it took longer to
print than it did to
design and used up part of a reel of rather old
PLA I had sitting around. I coated it in marine varnish, as PLA is a bit
hydroscopic, and assembled it with lots of outdoor sealant.
This is obviously only the beginning of a whole new story...
Understanding the problem...
Add some aerials
The HF whip may have been a slight error of judgement. It is the SIGMA
EUROCOM SE-HF-X80 and it gets good reviews but it's a lot bigger in real
life than I imagined. Six meters is very tall in a domestic environment and
watching it wag in the wind is, um, educational. However it tunes well on the
ATU and pulls in a lot of good stuff. It's on the rotator mast because I wanted
it in the middle of the house to help with current 'safety' rules so I have an
omnidirectional vertical that I can rotate. <sigh>
Inside the roof all the feeders go through my home-made water traps (two back
to back sockets separated by M3 bolts to give a horizontal air gap) and ensure
that the ever so hard to replace big fat feeders running down through the house
to the office are protected from that nasty wet stuff.
However... That doesn't address the problem that when it is blowing an easterly
gale, not so uncommon on the English Channel coast, it blows the rain back up
under the tiles and I am reliant on the felting to stop it getting into the
house. I wanted to tape and sealant the felting to the pole but that lovely
lead 'chimney' is tight on the sleeve and to lift it off I will have to
dismantle a whole lot of aerials over a few theoretical drops of water running
down the outside of the sleeve... I just need a trap to catch it. So I sketch
out some ideas, fire up the openSCAD solid modelling software and 3D print a
part to do the job. It's not complicated. In fact it took longer to
print than it did to
design and used up part of a reel of rather old
PLA I had sitting around. I coated it in marine varnish, as PLA is a bit
hydroscopic, and assembled it with lots of outdoor sealant.