As of October 9th 2018, 3V8SF station is equipped with a 17m
Toploaded Vertical antenna for TX and two beverage antennas for RX:
- 260m Long Beverage, 2m high, beaming NA
- 160m Long Beverage, 2.2m high, beaming JA
- Network of BOGs
- 4 Square Receiving Array
Maximum TX Power: 100W
The DXCC-WAS-WAZ page summarizes
the achievements done so far.
The Audio Clips page include
audio recordings of some DX QSOs I managed to record.
Network of BOGs
Putting in place beverages to cover all main directions
would be tough to achieve without access restriction to
people and being too visible. For that reason I went for
a network of 4 BOGs (with the possibility to add
another one to Africa).
The BOG switching is performed from the shack through
RG45 connected to Arduino Uno on one side and to a
4-Channels relay module on the other side.
The arduino Uno is connected to laptop through USB. A
interface I developed switches the BOG directions.
The BOGs have different lengths since I'm still
experimenting trying to find out the optimum length for
the location. Currently, the BOGs range from 61 to 110m
An RF Choke from Remote QTH is placed upstream the 75
Ohms coax cable to shack.
The BOGs have good directivity. The audio recording
below is for 9J2LA located at 160 deg Az. It was
recorded using the BOG at 165 deg with a switching back
and forth to the other directions at 40, 80 and 315 deg.
Building a 4 Square Receiving Antenna
After trying Beverages and BOGs, I wanted to build a
receiving antenna with relatively limited real estate
requirement while ensuring 4 directions coverage. The 4
Square seemed to be a good alternative.
4 Square Receiving at 3V8SF
I did my own design on 4NEC2 of the targeted 4 Square
Array which was based on W8JI elements. The elements
spacing is 21m.
Array Elements arrangement
Each elements is made up using a 6.5m fishing rod and
four 8m long top hat loading. Two on-the-ground 20m
radials are attached to each element.
Expected array pattern
A lot of effort was made to bring each element to
resonate at 1830kHz targeting 75 Ohms +/- j8 using a
coil and a set of resistors. This was unfortunately not
achieved yet and I stayed within +/- 2 Ohms from the
required 75 Ohms.
SWR measurement on the 4
Electrical quarter wave feedlines were thoroughly VNA
measured and used for each element.
Delay lines for the cross-fire arrangement were cut as
follows; 30 deg for the side elements and 60 deg for the
rear element. The front element had 0 deg phase shift.
Using a signal source placed at 2 WL from the center of
the array, I managed to measure the F/B of this array to
be 21 db and and F/S of 19 db (North direction).
Although the targeted performance goes beyond that, more
effort is to be made to make the elements matching very
close to 75 Ohms.
Thanks to Ahmad 3V1B and Majdi 3V1M for helping in the
set up of the elements. Also to K7TJR, W3LPL and W0FLS
for the valuable technical support.
Update: On the air F/B Testing (Switching
manually, takes 3 seconds)
(K1KI) Beaming East then changes to West at 00:18, K1KI
is at 45 deg from the East position of the 4SQ
(F5IN) Beaming North, South at 00:22, North at 00:57, South at 01:13
Measuring Ground conductivity at 3V8SF
In order to better assess antenna performance, ground
conductivity measurement had to be conducted. To do so,
two 1m steel probes were pushed in parallel into soil.
An antenna analyzer measured the complex impedance which
was found to be 56.5+j17. I have used DL1GLH's
calculation on his website to convert that to
conductivity which is found to be 21.7 mS/m. Of course
this is not very representative of all the soil around
the antenna neither the entire earth depth but should
give some indication.
Radiation patters: Blue for
City QTH, Red for current 3V8SF QTH
I here above compare antenna radiation pattern of my TX
antenna between city location and current 3V8SF
location. The take-off angle goes from 35 down to 19.9
160m Top-loaded Vertical in 3V8SF
Preparing for the new season, I designed and built a
top loaded vertical antenna for 160m in 3V8SF
location. The antenna is 17m high with two top loading
wires 12m each. For instance, the antenna has 8 radials,
19m each. A shunt match coil is added at feedpoint.
First testing night QSOs - 21/09/2018
First measurements showed that the wire interacts with the metallic hanging mast
so I had to put it 1.5m away then adjust the hairpin match again.
The map above shows the stations I could QSO during the night of September 21st.
The antenna performed really well with 100W only. Unfortunately, the beverage
antenna was disconnected.
3V8SF as RXed by VY2ZM 00:43z
3V8SF QSO with FR4NT 01:32z
260m Beverage Antenna beaming North
I installed this beverage for experimental purposes. It
was used in Spring Stew Perry DX Challenge to check the
performance listening to NA station (antenna beaming).
The location is approximately 100km away from 3V8SS
where the TX Inv-V antenna is.
26 Ground spikes were prepared in advance. 1m long PVC
pipes were hooked up on the spikes partially buried. Due
to some constraints, the beverage length was limited to
240m beaming North America (at 291 deg). One ground rod
(1m long) is installed at each antenna end. The receiver
end has 2 radials (15m).
The antenna was connected to Reverse Beacon Network
(3V/KF5EYY). After 5 days of receiving, data was
gathered for 160m. Calculation were made on Excel to
turn raw data into station locations. The map below
shows the received stations. The circle size indicates
the average signal strength from the region. The signals
from North America were good compared to those of much
closer European stations!
During the Spring Stew Perry, I was operating from 3V8SS
using an Inv-V for 160 while listening on the remote
beverage. European signals where clearly better on the
inv-V while no NA signal was heard on it. NA signals
were easily copied on the beverage.
Later on, the ground spikes were replaced by 2m long
steel tubes set up on small cement blocks. Wooden poles
were later fitted on the metallic supports. This has
improved the SWR curve.
The SWR curve of the beverage is plotted using Rig
Expert AA-30.ZERO and was found as below:
Signal Source and F/B Check
used a signal source of about 0,5W at 1834.4 KHz to
check the front to back of the beverage antenna.
The distance from both ends of the antenna is about 470m
on the same line.
The signal source was powered by two 9V batteries and
the antenna consisted of a 2m wire.
When plotting the radiation pattern of the antenna at an
elevation of 0.18 deg (corresponding to 470m distance
and 1.5m of elevation), the difference of Front to Back
was found to be around 8 db (See pattern plot at right).
SpectraVue has been used to record the FFT Spectrum from
RF Space SDR-IQ during the signal source transmission
for a later comparison of signal strength at the TX
According to the plots above, a difference of 7 db
between front to back can be noticed which is in line
with the plotted pattern at 0.18 degree (Blue line:
Front Signal, Red Line: Back Signal).
In order to check the maximum null, signal source should
be placed much higher in the air.