Topband: Broadband DHDL

[Ryszard Tymkiewicz]

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 at 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
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