The ALA100 was originally designed for the NDB listener. The recommend loop circumference of 20m was to provide an approx. loop reactance of 50 Ohm at 500kHz , this being a reasonable match to the ALA100 input z. Hence at > 1MHz to the loop reactance is higher than the ALA100 input z. Whilst this may look like a mis-match, the loops radiation resistance is lower with a rise in frequency, hence this gives a constant output verses field strength. One benefit of having a higher loop reactance compared to the amp. input z is that the loop doesn't shunt the amplifiers' feedback as much as a lower inductance would. Therefore, there is less degradation in the amplifier noise figure. However, this would normally not be an issue with ALA100 because the overall s/n would be set by the loop. Whereas, this starts to be an issue with 1m dia. loops.
Therefore, making the loop larger shouldn't cause a problem. But it may not be necessary with the new ALA100LN. The new ALA100LN serial Nos. 200 onwards are probably over engineered in terms of noise figure. This being approx. 0.33dB at 1MHz with a equivalent inductance of a 20m loop. However, this does mean that the new amp. will work well even with an 8m circumference loop. Also the new ALA100LN has a 23dB gain verses 17dB with the old ALA100s The ALA1530LN/P head amps. are basically the same as the new ALA100LN but with a higher gain of 26dB and a lower input z to match the 1m dia. loop. The loop/amp. noise figure above 2MHz is approx. 0.2dB or put it another way the noise floor is 12dB lower compared to the thermal noise of a resistor. 73 Andrew Ikin Wellbrook -----Original Message----- From: Volodya S Sent: Monday, August 27, 2018 5:55 AM To: Mailing list for the International Radio Club of America Subject: Re: [IRCA] Loop comparisons / suggestions Valid point from Chuck. I've never had an overload problem with any of my ALA. The FLG 100, yes. It needs the 10 dB attenuation, but the ALA 100 works fine, even with my 10 kW CFAX 1070 within 1 to 2 km from my QTH. Never any overload. 73, Walt On Mon, Aug 27, 2018 at 4:51 AM Chuck Hutton <[email protected]> wrote: > I'm not convinced that the impedance mismatch would change enough to make > a loop bigger than 20m be less effective than a 25m loop. > > I wonder whether Andy factored in overload and was saying "bigger might > cause urban overload problems". > > But this is speculation as Wellbrook doesn't really explain the 20m > limit.. > > > Chuck > > > ________________________________ > From: IRCA <[email protected]> on behalf of Nicholas > Hall-Patch <[email protected]> > Sent: Sunday, August 26, 2018 9:13 PM > To: Mailing list for the International Radio Club of America > Subject: Re: [IRCA] Loop comparisons / suggestions > > Wellbrook's documentation for the ALA100LN says "The antenna uses a 20m > circumference thin wire loop to provide optimum s/n. " Apparently, > larger > loops provide more of a mismatch to the input impedance of the amplifier, > so one doesn't get the expected additional gain from a still larger loop. > But they still work well with a variety of loop dimensions as various > posts > attest. > > best wishes, > > Nick > > On Mon, Aug 27, 2018 at 2:41 AM, R. Colin Newell <[email protected]> > wrote: > > > Andy Ikin would’ve told you that a standard ALA100 is probably at its > best > > at a loop of wire 20-30 feet long. > > > > Bigger is not always better with these units. > > > > Colin Newell - Victoria - B.C. CANADA - > > > > > On Aug 26, 2018, at 6:40 PM, Paul B. Walker, Jr. < > > [email protected]> wrote: > > > > > > I could’ve made it even larger but I wanted a cross between large size > > and > > > manageable I could’ve done 40-50 feet long. Who knows what I’ll > decide > > > to do when I end up somewhere else > > > > > > Paul > > > > > >> On Sun, Aug 26, 2018 at 9:39 PM Volodya S <[email protected]> wrote: > > >> > > >> Excellent dimensions, Paul. The larger the loop, the more gain you > will > > >> have. Mine are always as large as I can make it! ....Walt > > >> > > >> On Sun, Aug 26, 2018 at 11:44 PM Paul B. Walker, Jr. < > > >> [email protected]> wrote: > > >> > > >>> When I land somewhere again where I have a bit of yard space (i dont > > have > > >>> hear, but did at my last place) Im reconstructing my Wellbrook > ALA100LN > > >> 25 > > >>> foot long by 10 foot tall valleyball net loop antenna that worked so > > well > > >>> for me. > > >>> > > >>> > > >>> > > >>> On Sun, Aug 26, 2018 at 7:42 PM R. Colin Newell < > > [email protected]> > > >>> wrote: > > >>> > > >>>> Correction: The Wellbrook ALA series is optimized for 100khz to 30 > > >>> MHz..... > > >>>> not really 10 KHz - although you will hear lots of stuff < 100 KHz > on > > >> it. > > >>>> > > >>>> 100% satisfied Wellbrook user. > > >>>> > > >>>> Colin Newell - Victoria - B.C. CANADA - > > >>>> > > >>>>> On Aug 26, 2018, at 7:36 AM, Russ Johnson <[email protected]> > > >> wrote: > > >>>>> > > >>>>> > > >>>>> Good Morning, > > >>>>> > > >>>>> I will likely be purchasing a magnetic loop this fall. I wasn’t > able > > >>> to > > >>>> find much on the web in terms of direct comparisons between the > > >> Wellbook > > >>>> ALA1530LP, W6LVP loop and DX Engineering RF-PRO-1B. > > >>>>> > > >>>>> Ability to withstand the weather is of prime importance. While > cost > > >> is > > >>>> always a consideration, of equal importance are performance (of > > >> course), > > >>>> durability, product support, ease of installation and use. > > >>>>> > > >>>>> I’d love to hear any thoughts, experiences and suggestions. > > >>>>> > > >>>>> Thank you , > > >>>>> > > >>>>> Russ Johnson > > >>>>> Lexington NC > > >>>>> > > >>>>> > > >>>>> Sent from my iPad > > >>>>> _______________________________________________ > > >>>>> IRCA mailing list > > >>>>> [email protected] > > >>>>> http://montreal.kotalampi.com/mailman/listinfo/irca > IRCA Info Page - Kotalampi< > http://montreal.kotalampi.com/mailman/listinfo/irca> > montreal.kotalampi.com > Your email address: Your name (optional): You may enter a privacy password > below. 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