FEEDING THE ANTENNA
Feed the antenna with 50 ohm coaxial cable, braid connected to the bracket and the center
conductor conneted via solder lug to the coil. Coils can be wound for the following bands:-
0 turns = 14 MHz (20 meter band) (VSWR - almost 1:1)
2 turns = 10 MHz (30 meter band) (VSWR - almost 1:1)
6 turns = 7 MHz (40 meter band) (VSWR - about 1.1:1)
51 turns = 3.8 MHz (80 meter band) (VSWR - about 1.4:1)
52 turns = 3.75 MHz (80 meter band) (VSWR - about 1.4:1)
53 turns = 3.7 MHz (80 meter band) (VSWR - about 1.4:1)
54 turns = 3.65 MHz (80 meter band) (VSWR - about 1.4:1)
55 turns = 3.6 MHz (80 meter band) (VSWR - about 1.4:1)
56 turns = 3.55 MHz (80 meter band) (VSWR - about 1.4:1)
57 turns = 3.5 MHz (80 meter band) (VSWR - about 1.4:1)
In my case I decided to solder a solder lug to the center pin of an SO-239 Socket
which would then be attched to the stainless steel nut and bolt terminal at the bottom
of the loading coil and again fixed solid with some aradite expoxy glue. The electrical
connections will all then be sealed in silicone for weatherproofing.
Stage 2: The 7 MHz Loading Coil
The completion of winding of the HQ loading coil was made on 16/02/2008.
The photos below show the completion of the loading coil for the 40 Meter
Vertical Antenna.
The coil is wound on a 100 mm uPVC pipe that is used as the coil former.
Stainless steel nuts and bolts used for the coil connection points and 6mm insulated
copper wire is used to wind the 6 turns for the coil.
The coil was first set in place using "Sellery" nylon cable clips setting the coil pitch
spacing at 1 cm, these are stuck into place using AA glue. Once this is done the coil
is then smothered in expoxy glue to ensure no movement and that it is robust.
The shiny surface you see is the dried epoxy glue, although it is not asthetic,
it serves the purpose of strengthening the coil.
Photo above: Somewhat ugly (encased in epoxy), the 7 MHz HQ loading coil. The coil
connection points on left are staineless nuts and bolts.
Photo above: Close up of the "Sellery" nylon cable clips used to hold down the coil and
determine the 1 cm coil pitch.
Stage 3: Attaching the loading coil to the coil platform. Saturday 23/02/2008
Today I went to Reclamation Street to buy a piece of 150mm x 190mm Bakelite to
finish the modular coil platform. I also purchased some nylon nuts and bolts for the
fastening of the coil platform to the underside of the antenna.
The bakelite sheet was HK$10.00 and cut to order, nylon nuts and bolts were HK$1.50
each.
The two photos show the coil now glued to the bakelite and fastened to the nylon
platorm. A weatherproof case is also attached which has the SO-239 connector
affixed. This is almost now finished except for the wiring connections to the antenna
itself.
Photo above: Vertical view of the 7MHz coil glued to the baklite sheet and the afixed to the
nylon coil platform using nylon nuts and bolts. The SO-239 Connector box is also attached.
Photo Above: Side view of the 7MHz Coil Platform Assembly completed on 23/02/2009. Now for the wiring
work.
Stage 4 ~ 8th and 9th March, 2008 - Final Stages.
On Saturday I mounted the antenna pole on the roof along with the ground connecor.
A 5 foot heavy duty aluminium pole is used for the mast, tis was mounted to an existing
railing using 4 nos. of 4" staineless steel hose clamps.
I also reinforced the main vertical bracket section of the vertical by attaching a uPVC
bottom section in order to give additional strength to this section as the original diameter
of aluminium tubing used was thought to be a little under engineered. The photos below
show the strengthening of the bottom section of the aluminim braket section. The uPVC
tube is fixed rigidly to the aluminium tube by use of epoxy glue and silicone sealant.
Sunday 9th March I will concentrate on the final electrical connections of the coil to the
vertical element and if time and weather permits, the final assembly of the vertical,
measuring and erection of the antenna onto the mounting pole.
Photo Above: Shows the uPVC tube glued to the top element section using epoxy and silcone glue to
ensure no movement. The purpose id to strenghen the lower portion of the vertical antenna.
Photo Above: showing the top section of the uPVC reinforcement section just before the connection points
for the upper tubing sections.
Photo Above: Shows the bottom Vertical Antenna mounting bracket in relation to the reiforced section.
The photos below show the 7MHz Antenna Mounting Pole and grounding put into place
and ready to receive the antenna.
Below are two photos showing the antenna first mounted on it's pole late afternoon on
9/3/2008, the Hi-Q base loading coil and platform can be clearly seen underneath.
Finally, the whole antenna was erected, connected up and coaxial cable connected at 5:45pm
on 9/3/2008 and I was able to test out the SWR. A flat 1.5:1 SWR across the SSB portion of
7MHz, not to bad for a homebrew antenna effort. With a little tuning on the antenna tuner it is
1:1 on the SWR meter. Now I need some propagation to test it. The photos below show the
antenna completed at twilight, it stand over 17.5 feet in the air.
POST INSTALLATION NOTE: 11/3/2008 ~ Further Adjustment of the connection leads and
the ground return wire yielded an SWR reading of 1.15:1 !!! I can't expect more.
A magnetic transformer should not be used with an antenna, which is alomst resonant at the operating frequency and thus very close to 50 ohm impedance . In that case the impedance will be transformed down to 50/10 = 5 ohm which may be difficult for the tuner to handle.
This morning I put up a Sony AN-1 Wide Range Active Antenna on my roof for shortwave listening. Saturdays are great for antenna work since I have a 5 day work week. The antenna is a wide range active antenna with a frequency coverage of 0.15 ~ 30MHz and has a controller box in the shack side which powers a preamplifier for the antenna, there is a switch which can deactivate the amplifier on the controller (-20dB when switched off). The preamplifier in housed in the antenna module and is a FET. I decided to install it in a horizontal position facing due North to gain coverage of Eu and Stateside.
The AN-1 is no longer made by Sony, it was replaced with the AN-12 which is basically the same antenna which I believe is also no longer available also, but may be available as NOS from some places. These antennas fetch between US$138 to $170 (Postage not included).
The roof side antenna houses the amplifier and a telescopic whip which is just 1.5 M long when fully extracted. It is powered by a 9V adapter or the equivalent in pen light cells. It is very easy to install and I had the antenna installed and up and running inside of 15 minutes.
Today, daylight DX was not particularly good as DX stations were few and suspect that propagation is not too good, so I was not able to do much of an acid test and compare it with my full sized passive vertical, but from the few stations that were present ,it do quite a good and decent job at pulling the stations in although there was obviously a bit more noise and fading when compared to the vertical. This was connected up yo my Lowe HF-150.
The true acid test will come this evening when I will listen to the night time DX and compare the differences with full sized antennas. Will report more.
There is also a whip antenna coupler for use with the AN-1, this slips over the whip antenna of the portable radio and connects via a cable to the antenna controller, so this is indeed a very versatile antenna.
