Re: [IRCA] [NRC-AM] Reversible Double-Delta

[neilkaz <neilkaz@xxxxxxxxxxxxx>]

Sounds like it was working well and good to hear that there basically was little re-nulling needed. This is a very important aspect of this design since SDR users want to record the entire band. On mine at home using fixed resistors I can get 30+ to 40 dB nulls on locals. This means most back nulled regionals go away at night as they are overwhelmed by DX from the desired direction. 

You can always phase it vs something else if a single freq very deep nulls is needed. When I got KCEG on 780 14 miles NNW of WBBM, I phased one of these vs a random piece of wire about 30 ft long on the ground. 

Non SDR users would do very well phasing one end of a Double Delta (Double KAZ or whatever you want to call it) vs the other. Nulls clearly exceed 40 dB, but are very narrow banded..ie basically just the frequency nulled +/- not much more than 10 KHz. The phased configuration is also bi-directional since you switch the phasing to null the opposite direction. 

140 ft length is likely the max for good high band F/B as it seems to worsen if you make the antenna much larger. 

73 KAZ

-----Original Message-----
>From: Mark Durenberger <Mark4@xxxxxxxxxxxxxxx>
>Sent: May 18, 2014 10:13 PM
>To: MNDXC <MDXC@xxxxxxxxxxxxxxx>, "DX @NRC" <am@xxxxxxxxxxx>, DX-IRCA <irca@xxxxxxxxxxxxxxxx>, Shafer Mike <mikegjco@xxxxxxxxx>, Baumgartner Fred-ARRL <K0FMB@xxxxxxxx>
>Subject: [NRC-AM] Reversible Double-Delta
>
>This evening, 3 Phools in the Phield set up a reversible 140-ft. 
>Double-Delta antenna at a quiet place in Burnsville MN.  The goal was to see 
>what sort of nulling we could do off the "backside" of the antenna (whether 
>the "backside" was the North end or the South end).  Think of it as a 
>super-hot loop antenna, but unidirectional in pickup rather than 
>bi-directional.
>
>It works.
>
>On a number of frequencies we were doing armchair copy of one station; flip 
>the antenna and the first disappeared while another came up just as 
>well...from the opposite direction.
>
>We were oriented North-South since most of our local pests were North of us.
>
>Antenna reversal is as simple as flipping a switch.
>
>Interestingly...the null held up across the band; little or no re-nulling 
>was needed.
>
>Surprisingly, we could do no better than about 27 db nulls of local 
>stations.  Our conclusion was that the Double-Delta seems to like low- and 
>medium-angle skywave and doesn't discriminate as well with strong 
>ground-wave signals.
>
>We will also investigate whether the extension of the null pot and RF 
>takeoff VIA UNEQUAL LENGTHS OF CAT-5 degrades the null.  (I've seen better 
>than 40 db null on these guys when the null pot is right at the leg of the 
>antenna; in this case we had run 150 ft. of Cat-5 to get to the receiver.)
>
>Mike Bates and Jim Dale may chime in with their own observations.  It was an 
>evening well-spent.
>
>Regards,
>
>Mark Durenberger, CPBE
>
>
>_______________________________________________
>Am mailing list
>Am@xxxxxxxxxxx

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