David & All,
I've been using broadside DHDL's since 9 years. The configuration was
like is described in IV3PRK article :
"The distance between Deltas is about 95m. Resistors are 1250 ohm ,
tranformers 12:1 bifilar windings ,2 pieces of coax 75 ohm each one 50m
connected together to transformer 2:1 and to 75 ohm coax. I used similar
fishing bats...8m high but I removed the last thinest part , so they are
7,1 m high attached to 2m high steel elements. The wire is 0,7mm CU. "
Now I changed a few things...the distance between DHDLs is 85 meters , I
made new transformers 12:1 with BN73-202 instead of toroids with bifilar
windings. Also I changed "magic T" transformer to BN73-202.
Answering your first question..the resistor is in the lower corner of
DHDL just opposite of a transformer in my case about 2 meters from a ground.
Answering your third question...in a broadside configuration you are
using just two equal pieces of a coax and at least in my case "magic T "
transformer
to connect them together. I use 2 x 50m of 75 ohm coax.
First I was using the antenna without a preamplifier but later I added
14dB gain Norton one and it is more comfortable when you have some gain.
Without the preamplifier sometimes I was not sure if the system is
working because a noise was so low.
In my case these DHDLs have been much quieter than 300m beverage but I
have soil with very good conductivity and usually beverages
are not working here very well.
So, thanks to George AA7JV who described the single DHDL ( TX3A) and
later Louis IV3PRK who wrote an excellent article about phasing them I
feel I have really good RX antenna here thanks to them.
73 Rys
SP5EWY
W dniu 2019-07-27 o 22:04, GEORGE WALLNER pisze:
David,
I have modeled both side-by-side and in-line phased DHDL arrays, but I
have only tested the in-line version.
NEC indicates that a RDF of 12 dB is possible. The in-line DHDL array
that I have tested was good, but I did not measure the RDF.
For phasing I used a magic T splitter with one of its outputs going
through 180 degree transformer. The "front" antenna had a longer
feed-line to compensate for the propagation delay, which is
proportional to the distance between the two antennas. (Allow for coax
VF.)
The DHDL receives from the transformer end. The terminating resistor
is placed at the other end (back-end). For best results the antenna
should be made quite symmetrical across its center. To get the best
front-to-back ratio you can tweak the loading resistor. I use a small
1.8 MHz transmitter which is placed about 1000 feet behind the
antenna. (The transmitter should be "outside" the near-field.)
73 and GL,
George,
AA7JV
On Sat, 27 Jul 2019 17:44:46 +0000
"Rodman, David" <rodman@buffalo.edu> wrote:
My QTH is awkward for putting additional beverages BUT I am intrigued
by the DHDL if it can be phased broadside (I have enough room for
that), per the reference from IV3PRK:
http://www.iv3prk.it/user/image/..-rxant.prk_tx3a.pdf
I have a few questions that would need to be answered.
1. Where in the physical layout of the antenna is the terminating
resistor located?
2. I could build the transformer to match, but does anyone know a
commercial product that would do the 12:1 transformation??
3. What would be the details to phase and combine the two (what
length?) antenna feed lines to a 50 or 75 ohm transmission line to
the station with a 2 antenna broadside configuration??
Thanks.
---
David J Rodman MD
Assistant Clinical Professor
Department of Ophthalmology
SUNY/Buffalo
Office 716-857-8654
_________________
Searchable Archives: http://www.contesting.com/_topband - Topband
Reflector
_________________
Searchable Archives: http://www.contesting.com/_topband - Topband
Reflector
_________________
Searchable Archives: http://www.contesting.com/_topband - Topband Reflector
|