Re: Topband: DHDL

[Martin Kratoska]

oops, the images didn't come thru. See here:

http://www.ok1rr.com/public/DHDL_OPT.NEC
http://www.ok1rr.com/public/antview.png
http://www.ok1rr.com/public/dhdl_opt-ver.png
http://www.ok1rr.com/public/dhdl_opt-hor.png
http://www.ok1rr.com/public/dhdl_opt-3d.png


73,
Martin, OK1RR



Dne 30. 06. 19 v 20:51 Martin Kratoska napsal(a):

That statement doesn't agree with my quick modeling

just read a few articles about DHDL antennas. One article states, the 
cut off frequency where the antenna becomes useless is when the 
overall length of wire reaches a 1/4WL... 


my results attached

73,
Martin, OK1RR

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Re: Topband: DHDL

[Martin Kratoska]

That statement doesn't agree with my quick modeling

just read a few articles about DHDL antennas. One article states, the 
cut off frequency where the antenna becomes useless is when the 
overall length of wire reaches a 1/4WL... 


my results attached

73,
Martin, OK1RR
CM Double Half-Delta Loop RX Antenna
CM By George Wallner, AA7JV
CM used at Chesterfield DXpedition TX3A
CM optimized by OK1RR
CE
SY h=1.5
SY vh=3.700271
SY l=17.79364
SY R=1126.759
GW  1   10  0   0   h   0   0   h+vh5.e-4
GW  2   10  0   0   h+vhl   0.1 h   5.e-4
GW  3   10  l   0.1 h   2*l 0   h   5.e-4
GW  4   10  0   0   h   l   0   h   5.e-4
GW  5   10  l   0   h   2*l 0   h+vh5.e-4
GW  6   10  2*l 0   h+vh2*l 0   h   5.e-4
GE  -1
LD  5   1   0   0   5800
LD  5   2   0   0   5800
LD  5   3   0   0   5800
LD  5   4   0   0   5800
LD  5   5   0   0   5800
LD  5   6   0   0   5800
LD  4   6   10  10  R   0
GN  2   0   0   0   13  0.005
EK
EX  6   1   1   0   1   0   0
FR  0   0   0   0   1.820
EN
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Re: Topband: DHDL

[Grant Saviers]

That statement doesn't agree with my quick modeling (I also wondered why 
my 40' base had some observed benefit on high bands now and then).  Both 
a 60' for 160 and 40' for 80/40 worked fine.


for a 60' baseline, 6' Z bottom wire, 30' Z to top or about 190' of wire:

Freq Gain dbi F/B db peak ang

1.8   -31 12 20
3.5   -16 15 25
7.0   -4  9  30
10  elliptical broadside about 5 to 10db F/S, 25 deg elev
>14   spikey pattern broadside and low vertical gain, maybe not useful

EZNEC 4.2 over average soil.  With higher conductivity soil, F/B 
improves a lot, and gain a few db.  Patterns are about the same.


Grant KZ1W

On 6/30/2019 9:03 AM, Martin wrote:

Topbanders,
just read a few articles about DHDL antennas. One article states, the 
cut off frequency where the antenna becomes useless is when the overall 
length of wire reaches a 1/4WL. In my understanding the original 
dimensions , 2*7.5m vertical plus 22m horizontal plus 2*13.3m sloping 
wires equals 63meters, which is already a lot longer than 1/4WL on 160m. 
What did i miss?



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Re: Topband: DHDL

[GEORGE WALLNER]

Martin,
Two things:
1. The antenna does not become "useless" when the loops are longer than 1/4 
wave. It just won't work as a DHDL, but may still be useful as a low noise 
RX antenna.
2. The DHDL is actually two loops, and each loops should be shorter than 1/4 
wave. Note that there is nothing special about the dimensions. You could 
make it smaller, to make it more suitable for 80 and 40. The dimensions 
originally published were set to maximize the signal output on 160.
One thing that's important: the two loops should be exactly the same size 
(within a couple of inches)! You can easily achieve that my moving the 
central crossing to the exact center.

73,
George,
AA7JV

On Sun, 30 Jun 2019 18:03:23 +0200
 Martin  wrote:

Topbanders,
just read a few articles about DHDL antennas. One article states, the cut off 
frequency where the antenna becomes useless is when the overall length of wire 
reaches a 1/4WL. In my understanding the original dimensions , 2*7.5m vertical 
plus 22m horizontal plus 2*13.3m sloping wires equals 63meters, which is 
already a lot longer than 1/4WL on 160m. What did i miss?

--

Ohne CW ist es nur CB..

73, Martin DM4iM
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Re: Topband: DHDL matching Transformer

[jeremy maris]

Hi Trevor,

Luis IV3PRK has good info on DHDL, based on the original by George Wallner, 
AA7JV
See http://www.iv3prk.it/TX3A-DHDL.htm

I use a 1200 ohm terminating resistor;  source resistance is about 900 ohms.  
900/75 = 12 so turns ratio to match is 3.5:1I use a 2 turn primary and 7 
turn secondary on a BN73-202 core.

Make sure that you have a feedline choke near the feed to the DHDL so you don’t 
get common mode noise.

They work well!


> On 28 Nov 2017, at 15:07, MR TREVOR DUNNE  wrote:
> 
> Hi All
> 
> My quest to better my station continues I want to try a DHDL can someone 
> recommend a matching Transformer and what size termination resistor should I 
> use,
> 
> I have some bn73-202 cores and I wish to use 75ohm feed line,
> _
> Topband Reflector Archives - http://www.contesting.com/_topband

—
Jeremy Maris G3XDK / G4AQG






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