[Lowfer] thoughts on PA0RDT "mini whip"

Thu Dec 22 14:26:51 EST 2016

Zack (& All) : Since you are also a microwave guy, there is a 130mH inductor 
in the old HP-430C and General Microwave equivalent that was used for the 
100kHz AC bridge circuit. If you ever need a low current high value choke 
for a VLF or LF preamp or other project, it may come in handy some day if 
you have any HP430C parts chassis lying around. I'm not sure how much 
current it will handle, but I would guess 10ma as being safe....

I also have found that coaxial common mode chokes can act like small ferrite 
loop antennas, so I shield them either with tin plate flashing or electrical 
junction boxes. I use ground isolated BNC connectors on my indoor CM chokes 
and have the conduit boxes bolted to a shelf in rack panel below my MF/LF 
converter.   The isolation transformer to the LF/MF converter is similarly 
in a galvanized conduit box that is ground isolated on the input side and 
grounded on the output side to the LF/MF converter and rack panel.  I have 
grounding connector cables to be able to ground both the shield and center 
conductor from the CM choke(s) in the rack panel to the AC service ground 
when the LF/MF antenna (EWE) is not in use.

I also have one of W1VD's modified e-probe antennas in use with the j310 fet 
that is used for various boat anchor radios in another room on the opposite 
side of my basement. I have ground rods about tem feet apart near my house 
end of that RG-6 cable run. Originally the e-probe was located near these 
ground rods about 25 feet from the house but I decided to move it another 60 
or so feet north to a different small tree location. The far end of the 
cable to the J310 modified e-probe goes to a set of shielded CM chokes and 
15~20ft of RG-6--- then goes to the e-probe up 15 feet or so just above a 
small tree.  I did not put a ground rod at this e-probe location as I was 
not sure it would be the final installation position. So I used an aluminum 
plate about 24 inches square as a grounding plate on the e-probe side.  When 
I first moved the e-probe to that more distant location I was noticing it 
would start to quickly pickup a static charge which could be heard on the 
antenna whenever a storm was approaching. Adding the grounding plate at the 
e-probe side of the choke stopped the static noise on the e-probe.  SM5BSZ 
has some "sensors" videos on youtube where he uses a grounding plate on an 
e-probe to test various locations around his house for antenna placement vs 
noise level.  So I gave it a try....seems to work for my situation....

https://www.dropbox.com/s/h6b77ruibwqfqib/IMG_0482.JPG?dl=0

https://www.dropbox.com/s/emj9086fs3zc9jp/IMG_0483.JPG?dl=0

https://www.dropbox.com/s/408on9lhfvp80sl/IMG_0484.JPG?dl=0

Sensors Part 4 SM5BSZ

 https://www.youtube.com/watch?v=C65u7Pmz7a0

73 Mike wa3tts

----- Original Message ----- 
From: "Zack Widup" <w9sz.zack at gmail.com>
To: "Discussion of the Lowfer (US, European, & UK) and MedFer bands" 
<lowfer at mailman.qth.net>
Sent: Thursday, December 22, 2016 9:41 AM
Subject: Re: [Lowfer] thoughts on PA0RDT "mini whip"

> Any idea how it does compared with the AMRAD e-probe antenna? I built an
> AMRAD whip but have yet to put it up. Since I have the next week off from
> work and it might be unseasonably warm, this is probably a good time to do
> it.
>
> 73, Zack W9SZ
>
>
> On Wed, Dec 21, 2016 at 4:50 PM, Howell, Laurence J <
> L.Howell at conocophillips.com> wrote:
>
>> Doug, I have three or four probes up various trees, some just separated 
>> by
>> 5m or so, but as ever, the selection of the height and location sweet 
>> spot
>> for best s/n is manifestly important here. A few feet either way can make 
>> a
>> hooge (hooge) difference  - I ve run various shoot outs on what works 
>> best
>> and though we get the odd earlier long haul decode on 475 with the 
>> highest
>> probe (50ft or so), the best here is one at around 35ft or so called 
>> "Aces
>> high" - slightly higher than RDT states but I do see that curve too in 
>> s/n
>> using NDB and W&G test set.
>>
>>  It took me a season or two to get just the right tree. Out of all the
>> antennae here the probes tend to work best over active or passive large 
>> or
>> small loops but that's probably because of the bespoke nature of the E/M
>> interference fields on this acre and related to off site man made
>> electrical noise sources. It will be different elsewhere - what works 
>> best
>> here wont elsewhere.
>>
>> I figured out that the best type of tree to have one on is the Genus
>> "Acacia" - which is pan-global and typically the worse is the Coconut 
>> Palm.
>>
>> I see a lot of comments on they are just mickey mouse appliance antenna
>> but Ive been using them in military and commercial situations for over 35
>> years and its horses for courses, and they work best here (and in a lot 
>> of
>> other countries around the globe) over anything else. Stat. Used to use
>> them in Antarctic for air-to-ground ops when the main wideband or LPA 
>> were
>> snow static bound....
>>
>> I ground the RG6 where it typically hits ground (boggy ground into a lake
>> typically), large series J common mode choke at that end, another in the
>> shack, keeping the power injector away from noisy mag fields that intrude
>> even metal ali boxes, then Bino isolated transformer which is usable at
>> 1kHz up to 500kHz or more - quite a few turns on 73 material from memory.
>> Power is battery though simple unstab DC from 110VAC is pretty good if 
>> you
>> decouple well. Playing with the voltage from 9-18VDC can help with iMod -
>> mine appears happy around 15V but my local blow torch on 1430kHz appears 
>> to
>> have a issue with pins stuck in its coax quite often :-) (joking)
>>
>>
>> Laurence KL7L
>>
>>
>>
>> -----Original Message-----
>> From: Lowfer [mailto:lowfer-bounces at mailman.qth.net] On Behalf Of N8OOU
>> Sent: Wednesday, December 21, 2016 1:32 PM
>> To: Discussion of the Lowfer (US, European, & UK) and MedFer bands <
>> lowfer at mailman.qth.net>
>> Subject: [EXTERNAL]Re: [Lowfer] thoughts on PA0RDT "mini whip"
>>
>> Doug,
>>
>> The mini whip is mounted and grounded to the top of a galvanized steel
>> trellis that I grow hops on. The trellis is about 15 feet tall, and
>> grounded at the base. RG-6 quad shield coax is grounded at the mini
>> whip/trellis, and runs back to the shack. Nothing in the shack is
>> externally grounded. I'm not sure if the DC power supplies ground back
>> to the mains.
>>
>> 73   de   N8OOU - Mike Meek
>>
>> On 12/21/2016 03:55 PM, Douglas Williams wrote:
>> > Mitch & Mike,
>> >
>> > Thanks for the info.
>> >
>> > Mike, did you ground the antenna at the base, halfway point, or at the
>> > house?
>> >
>> > Anyone else have any info, feel free to chime in.
>> >
>> > D. KB4OER
>> >
>> > On Wed, Dec 21, 2016 at 4:48 PM, N8OOU <n8oou at meekfarm.us> wrote:
>> >
>> >> Doug,
>> >>
>> >> A few observations on the mini whip.  I built one from my junk box 
>> >> parts
>> >> based on the original design. I had to add a notch filter to block my
>> local
>> >> 500W AM BCB station. Inserted in the whip between the FET and Buffer
>> amp. I
>> >> also must use a 500 Khz low pass filter at the receiver for LF. I have
>> it
>> >> mounted about 15 Ft above ground, away from the house, and grounded
>> >> according to common information found on the web.
>> >>
>> >> It works (all the way up to 10m), better than a long random wire, but
>> not
>> >> as good as the Low Noise Vertical I just finished.
>> >>
>> >> 73   de   N8OOU - Mike Meek
>> >>
>> >>
>> >> On 12/21/2016 03:07 PM, Douglas Williams wrote:
>> >>
>> >>> Have any of you used one of these on VLF/LF? What are your 
>> >>> experiences?
>> >>> They seem to be everywhere on eBay, from kits to fully assembled, and
>> >>> averaging $12 - $40.
>> >>>
>> >>> D. KB4OER
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