Re: [IRCA] Working on the problem

[Russ Edmunds <wb2bjh@xxxxxxxxx>]

If the "textbook" number of turns on a given size frame is x, and you use a two turn link/pickup coil ( which is the usual number ) you will now have "x + 2", and may need to reduce the number of turns needed in order to reduce the "L". That will be pretty obvious as the loop won't tune the whole band. If x = 10, then using a link/pickup coil, you will likely need 8. 

One of mine is amplified with a dual-balanced FET amp ( 2N4416's IIRC ), and it is directly coupled. When I used it unamplified, I added a two-turn link coil, and had to reduce the main/tank coil accordingly. I never tried using a link coil with an amplifier.

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: Re: [IRCA] Working on the problem
> To: "Mailing list for the International Radio Club of America" <irca@xxxxxxxxxxxxxxxx>
> Date: Sunday, April 10, 2011, 1:45 PM
> Thanks Russ.
> 
> The  mixed loop is more for fine tuning the preamp
> than any permanent solution, leftover 1x2 from another
> project and notched for the wires with a miter saw. Quick
> and dirty. Since the varactors are switched between the 2
> loops the smaller loop doesn't seem to interfere with the
> larger one though below about 5MHz there doesn't seem to be
> a null on the smaller one. I have some Litz coming and plan
> on doing a 3' MW loop separate from any other antennas.
> 
> Null is sharp on MW and I can detect a station at 1120 with
> very little of 1140 blasting in here so the Q isn't that bad
> either. I think replacing the 26 gauge vinyl covered wire
> taken out of some old Cat 5 with Litz and getting rid of the
> inner loop would be a big improvement on it's own.
> 
> The Preamp is sensitive enough that I get decent reception
> by hooking 5' of wire to each side through a 33pF cap on HF
> feeding my modded S350DLX. Hmmm, 10' length of leftover
> Copper pipe.. I think a stealthy vertical dipole is in mu
> future :D
> 
> I have a roaring sinus headache but my next experiment is
> to use the inner 4 turn CT winding as the pickup for the MW
> loop. I'll try that this evening if this headache goes
> away..
> 
> Tim
> 
> On 4/10/2011 8:48, Russ Edmunds wrote:
> > 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
> > 
> > 
> 
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