Topband: High performance RX antenna at T6LG

Thu Feb 14 13:09:59 EST 2013

Hi Top-banders 

I just got this skype IM for Ilian T6LG and I would like to congratulate
Ilian for his dedication on all aspects of Ham radio.

hi Jose

[12:02:50 PM] Ilian: My log is already uploaded on LoTW and ClubLog

[12:03:23 PM] Ilian: 1394 QSO on 160m

[12:04:15 PM] Ilian: more than 1200 QSOs after RX antenna installing

[12:05:02 PM] Ilian: about 150 QSOs without RX antenna for more than 2
months on the air

[12:05:57 PM] Ilian: 1200 QSOs made with RX antenna for 1 month and 10 days

[12:06:49 PM] Ilian: 68 DXCC worked on 160m during the all operation

[12:07:49 PM] Ilian: about 40 countries worked after RX antenna installing
within 1 month and 10 days

[12:09:49 PM] Ilian: 3865 QSOs on 80m during the all operation, about 2500
worked after RX antenna installing

[12:10:24 PM] Ilian: 112 DXCC worked on 80m for whole period

[12:11:54 PM] Ilian: about 50 new DXCC worked after RX antenna installing
for a month and 10 days

[12:13:36 PM] Ilian: http://t6lg.com/?page_id=221

[12:14:05 PM] Ilian: you can see all statistics here

[12:15:57 PM] Ilian: Thank you, Jose!

Here a little tail about this high performance RX antenna. Ilian was
operation in a military campus, you can see the pictures on his website 

www.t6lg.com

The noise level was unbearable for low bands, Ilian was not able to hear
even the strong European station but Ilian had a good signal on low bands. I
worked him on 80m back in October and start chatting with him on skype. I
proposed a flag antenna to improve his RX capabilities.

The problem with most field station is lack of good ground, this issue makes
a very complicated situation with common mode noise everywhere, from the
coax cable feeding the inverted V to the AC wire system and power
generators, and other antenna cables. There is not a simple way to ground
the receiver, every wire connected to the radio became  part of the antenna
system.

The solution was a system , not only a simple flag antenna. Ilian radio is a
FT897 that does not have a separated RX port. I send him a DX Engineering
RTR-1 Receive Antenna Interfaces RTR-1, that switch was necessary to keep
high isolation between the RX antenna and the TX antenna. The flag antenna
has low gain and I sent Ilian a preamp made by Gary KD9SV, a FET follower
design with high IP3.

The parts for the antenna was very simple, a 9"1 balun and a 910 ohms
resistor, and a 100 to 75 ohms BALUN to feed the preamp. The key component
here was the CAT 5 single twisted pair to feed the flag antenna without any
common mode noise pickup (it is necessary to strip the CAT5 and separate
each of the 4 pairs), a coax cable won't work in high noise environment,
even with a killer choke the ground does not help to stop the common node
noise. That was not the first time a twisted pair saved the day, two years
ago  I suggested Rolf PY1RO a similar antenna fed with twisted pair that
worked very well, bringing the noise to zero in a s9+20 noise environment.

The Delta Flag antenna built by Ilian was very similar the RX antenna used
by FO0AAA and described by K6SE. It is a triangle antenna (any size works)
with 24 ft base and hung from a single point that allows Ilian to rotate the
antenna.  Actually this feature was very desired, Bill W4ZV educated Ilian
about long path propagation on 80m and he made several very happy campus on
West Coast listening South for Long Path on 80m.

This antenna can be used on most of DX expeditions with no place for
beverages, a simple RX antenna made with CAT5 wire can be a high performance
antenna and a difference between no or few QSO's and few thousand QSO;s

A single flag is not the best antenna you can build, the RDF is modest  but
the secret is how to implement this antenna avoiding common mode noise, a
simple CAT 5 twisted pair can make a huge difference.

I see no reason for a DX expedition to complain about noise on low bands,
CAT 5 can be found anywhere and it is vey light.

P.S. I was not able to work Ilian on top band, never had the spotlight.

Regards

Jose Carlos

N4IS

Delta RX Antenna used by FO0AAA

from Earl, K6SE on June 1, 2000 

View comments about this article! 

Several subcribers inquired about the Delta 160-meter receiving antenna used
at FO0AAA. 

It is a close relative of the Pennant and Flag antennas, which are
ground-independent relatives of the Ewe. The Delta is a modification of the
"delta-shaped Ewe loop" shown in figure 7-66 on page 7-51 of ON4UN's new
Low-Band DXing book. 

I took John's Delta-Ewe and, with the feedpoint and termination located at
the bottom corners of the triangle, I used EZNEC to optimize the design for
best F/B and zero reactance at 1.830 mHz. This is the design that was built
by ON4UN for use by FO0AAA. 

It is a delta loop-shaped antenna with a 28-foot (8.537m) bottom horizontal
wire and the apex 17 feet (5.183m) above the bottom wire. That means there
is a total of about 72 feet (21.951m) of #14 AWG wire in the triangular
loop. 

The EZNEC design had the bottom horizontal wire 3 feet (0.915m) above
ground, therefore the apex was 20 feet (6.096m) above ground. It is a
ground-independent antenna, without the ground-related shortcomings of the
Ewe. 

The termination resistor, which goes in one of the bottom corners of the
loop, is 950 ohms non-inductive. The feedpoint is at the other bottom corner
and the feedpoint impedance is 950 ohms with zero reactance at 1.830 mHz. An
impedance matching transformer such as those previously described on the
Topband Reflector for use with the Pennant or Flag should be used with the
Delta antenna. 

The F/B ratio in the EZNEC model is greater than 40 dB and the cardioid
pattern directivity of the antenna is in the direction of the feedpoint end
of the antenna (the same as with the Pennant, Flag, or Ewe). The gain of the
antenna is about -34.5 dBi, so a receive preamp should be used with the
antenna. 

The primary reason this design was chosen by the FO0AAA team was that it was
an easily-erected and easily-rotated directional receiving antenna. Only one
support at the apex is needed (which must be non-metallic). The bottom
corners of the antenna can be attached and pulled taut with rope to tent
stakes driven into the ground. To change directions, it is a simple matter
to relocate the tent stakes to the desired direction and re-attach the
corners of the antenna. 

Unfortunately, this design was done too late to make it into an article
about Flags and Pennants I wrote for QST (which will probably appear in the
July 2000 issue). 

73, de Earl, K6SE