Re: [IRCA] Working on the problem

[Russ Edmunds <wb2bjh@xxxxxxxxx>]

Using the two loops on the same frame will degrade the performance for the MW portion and probably the SW portion as well. This is because the proximity of the windings pretty much ensures that each will 'see' the other and therefore the resulting patterns will be somewhat skewed and the nulls likely reduced.

I've used two air core MW loops in my basement shack - one 4' the other 2' for over 20 years and found that I needed to keep them about 4' apart in order to minimize unwanted interaction.


Russ Edmunds
15 mi NNW of Philadelphia  
Grid FN20id
<wb2bjh@xxxxxxxxx>
FM: Yamaha T-80 & Onkyo T-450RDS w/ APS9B @15'; Grundig G8
AM:  Modified Sony ICF 2010's barefoot


--- On Sun, 4/10/11, Tim Hills <thills@xxxxxxxxxxxxx> wrote:

> From: Tim Hills <thills@xxxxxxxxxxxxx>
> Subject: [IRCA] Working on the problem
> To: Shortwave-SWL-Antenna@xxxxxxxxxxxxxxx, Hard-Core-DX@xxxxxxxxxxxxxxxx, "Mailing list for the International Radio Club of America" <irca@xxxxxxxxxxxxxxxx>
> Date: Sunday, April 10, 2011, 1:21 AM
> Thunderstorms moving through tonight.
> Thought I'd jot down what I've learned and see if anyone has
> any thoughts on improvements or something else I might try,
> other than moving....
> 
> I've been experimenting a bit with pulling usable signals
> out of the RF soup I live in and thought I'd share some of
> what I have found works so far. If you haven't seen my
> earlier posts I have 3 5KW+ MW stations beaming directional
> converging in my back yard and hash from high voltage lines
> 60' from the house. Plus the usual semi-urban noise,
> routers, street lights, etc. Also, my "shack" is in the
> basement in conductive ground and the house has the
> chickenwire reinforced plaster. Small lot and I want to be
> as invisible as possible, everything in the low attic
> preferably. It's a challenge but it's keeping me out of
> mischief and honing skills I haven't used in a couple of
> decades. ;)
> 
> Changing both the preamp and loop from an unbalanced to
> balanced design really cut down the power line hash and
> going from JFETs (J310s)  to MOSFETs (3N200s) with
> appropriate changes in biasing on the inputs pretty much
> cured the intermod problems and gives a much wider gain
> control. The BF199 bipolars are the same in the output
> stage. 10mA quiescent collector current gives best results.
> 
> Air core and spiral windings seem more immune to the common
> mode noise from the power lines than a solenoid and with a
> tighter null. The lower common mode noise was counter
> intuitive to me but I think the lower distributed
> capacitance. It seems that in high ambient environments
> ferrite rods have their own quirks that I plan on
> investigating later.
> 
> Right now I have 2 loops on the same wooden frame. 14 turns
> CT covers the MW band, 4 turns CT covers from 3.5MHz to a
> bit over 10MHz. 4 MVAM109s in series/parallel for remote
> tuning, no pickup loop the signal is taken off the tuned
> loop directly through the very high Z inputs of the preamp.
> It's hung on a covered porch when in use with power, tuning
> and gain controls running through Cat. 6 cable.
> 
> Still working on the phased loop array. Better than 20 dB
> front/back ratio so far at 1000 KHz.
> 
>  No formal logs kept so far but I'm having more fun
> building than listening. Catch a station, go upstairs, turn
> the loop, is it better or worse? I need to get a
> rotator....
> 
> When I get something workable by the average homebrewer
> I'll post schematics and pics. When I work out the details
> of the preamp if there's enough interest I'll make kits
> available at cost/actual shipping.
> 
> Now, about that twin coax the previous owners had hooked to
> that dish....
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