Re: [IRCA] Reversible Double-Delta

[Walter Salmaniw <canswl@xxxxxxxxx>]

Can we see a schematic of this antenna?  73, Walt

On Monday, May 19, 2014, Mark Durenberger <Mark4@xxxxxxxxxxxxxxx> wrote:

> So perhaps it's the 140-foot size, rather than the use of Cat-5 extenders,
> that created the 15 db difference in F/B nulling.  Previously, I was doing
> better than 40 db at times with the 120-footer (though that WAS with the
> null-pot right at the antenna).
>
> Earl Higgins asked for some loggings; they're on the way.
>
>
> Regards,
>
> Mark Durenberger
>
>
> -----Original Message----- From: neilkaz
> Sent: Monday, May 19, 2014 1:45 PM
> To: am@xxxxxxxxxxx
> Cc: irca@xxxxxxxxxxxxxxxx
> Subject: Re: [IRCA] [NRC-AM] Reversible Double-Delta
>
> 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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