Send me an SASE, and I'll send you one, Chuck. Then you can measure it for
yourself.
73, Mike
www.w0btu.com
On Mon, Jul 16, 2018 at 5:50 PM, Chuck Hutton <charlesh3@msn.com> wrote:
> Tim -
>
>
> What spec on 73 material are you referring to? I have never seen a
> published Al value for the 287300292 (BN73-202). Here's the Fair-Rite page
> with the 287300292:
>
> https://www.fair-rite.com/product-category/suppression-compo
> nents/multi-aperture-cores/
>
> And here's the Amidon page for the BN73-202:
>
> http://www.amidoncorp.com/bn-73-202/
>
>
> The BN73-202 has been discussed before here and Al of 8500 was quoted.
> However, way back upon prodict release someone posted an Al od 2500. Kits
> and Parts quote an Al of 12000. My rqo caores have an average Al of
> 13,333. I;ve seen no manufacturer Al data.
>
>
> But bottom line I think we borh believe the true Al is higher than might
> be believed and therefore better low end response.
>
>
> Note these turns versus frequency curves:
>
> http://www.qsl.net/in3otd/ham_radio/160m_transformers/160m_trafos.html
>
>
> The 3rd chart down is the heart of the issue.
>
>
> Two turns is of the edge of the cliff. Better to use 3 turns I believe.
>
>
> Chuck.
>
>
>
>
> ________________________________
> From: Tim Shoppa <tshoppa@gmail.com>
> Sent: Monday, July 16, 2018 5:07 AM
> To: Chuck Hutton
> Cc: kd9sv; topband@contesting.com
> Subject: Re: Topband: Beverage transformers tht work down to 630 m
>
> I think the spec on 73 material permeability is also conservative. Few EMI
> suppressing customers suffer if the impedance is higher than guaranteed.
> The Fair-Rite 73 curves also show permeability peaking up even higher in
> the 500 kHz region.
>
> W8JI has in the past made some remarks about stray winding capacitance
> which would get worse with more turns. I believe his drawing shows some
> “dummy turns” put in on the far side of ground, to cancel the stray
> capacitance?
>
> An important advantage of fewer turns, is that you can use ordinary
> plastic insulated hookup wire or kynar wire wrap wire to put the small
> number of turns through the holes. If I use enamel magnet wire with these
> cores to get more turns I end up nicking the enamel insulation on the core
> corners.
>
> Tim N3QE
>
> > On Jul 15, 2018, at 8:49 PM, Chuck Hutton <charlesh3@msn.com> wrote:
> >
> > Yes, I think we all agree on the meaning of the 4X rule and the other
> basics.
> >
> > The mystery to me remains that a 1 turn transformer was good to 270 kHz
> in the Clifton data. I calculate at 500 kHz:
> >
> > 1 turn on a BN73-202 with Al = 8500 gives 9 uH
> >
> > 9 uH is only 28 Ohms
> >
> > For reference, 2 turns = 34 uH and 107 Ohms. 3 turns is 77 uH and 242
> Ohms.
> >
> >
> > So theory seems to tell me I need 3 turns.
> >
> >
> > Chuck
> >
> >
> >
> > ________________________________
> > From: kd9sv <kd9sv@comcast.net>
> > Sent: Sunday, July 15, 2018 4:43 PM
> > To: 'Chuck Hutton'
> > Subject: RE: Topband: Beverage transformers tht work down to 630 m
> >
> > Guys, the 4x rule is to my understanding that the measured impedance at
> the
> > lowest frequency to be used at should be at least 4 times the operating
> > impedance. In other words a 50 ohm system would require 200 ohms open
> > circuit impedance measured at the primary winding of the xfmr. If 2
> turns
> > only measures about 100 ohms then 3 turns would likely be close enough
> and 4
> > turns would also work and would measure 400 ohms which is 8 times the
> > operating impedance of the antenna system. My test equipment can only
> > measure down to about 450khz so below that I cannot give an opinion.
> >
> > 73, de gary...ps: the BN202-73 will likely work well with two/6 turns and
> > 3/9 for a 9:1 system for 50 ohms
> > -----Original Message-----
> > From: Topband [mailto:topband-bounces@contesting.com] On Behalf Of Chuck
> > Hutton
> > Sent: Sunday, July 15, 2018 7:26 PM
> > To: Tim Shoppa
> > Cc: topband@contesting.com
> > Subject: Re: Topband: Beverage transformers tht work down to 630 m
> >
> > Tim:
> >
> >
> > Thanks for digging that out. It makes me worry much less about using
> > BN73-303's with 2 or 3 turns in the primary at 630m.
> >
> >
> > My only problem is that I don't understand why the low end is so good for
> > the 1 turn primary. Using the "4x" rule for the transformer, 4 turns
> should
> > be needed.
> >
> > Since I don't understand the response and I don't care about the high end
> > response, I'm still tempted to use 4 turns and be sure.
> >
> >
> > Perhaps part of the answer is that reality and theory do not coincide.
> > According to the published Al, 2.7 turns is need at 500 kHz. to have 64
> uH
> > and satisfy the 4X rule. Yet my 3 turn windings measure 108 uH and 120
> uH.
> > That explains a good bit of the low end response.
> >
> >
> > Chuck
> >
> >
> >
> > ________________________________
> > From: Tim Shoppa <tshoppa@gmail.com>
> > Sent: Sunday, July 15, 2018 3:50 PM
> > To: Chuck Hutton
> > Cc: topband@contesting.com
> > Subject: Re: Topband: Beverage transformers tht work down to 630 m
> >
> > I agree the usual rule of thumb (Transformer winding Z should be several
> > times larger than nominal line impedance) would cause you to think you
> > should have more turns.
> >
> > The old Clifton Labs website is no more. But an archived page of
> > measurements of transformers shows that the frequency response extends
> well
> > below what you might think, from the rule of thumb. Archived page:
> > https://groups.io/g/BITX20/attachment/27529/0/clifton%20Labs
> %20IMD%20in%20Br
> > oadband%20Transformers.pdf
> > Clifton Laboratories 7236 Clifton Road Clifton VA 20124
> > ...<https://groups.io/g/BITX20/attachment/27529/0/clifton%
> 20Labs%20IMD%20in%
> > 20Broadband%20Transformers.pdf>
> > groups.io
> > Clifton Laboratories 7236 Clifton Road Clifton VA 20124 tel: (703) 830
> 0368
> > fax: (703) 830 0711 E-mail: Jack.Smith@cliftonlaboratories.com
> >
> >
> >
> > He finds that BN73-202 transformers wound with a single turn winding,
> have a
> > -3dB point at 270kHz.. A two turn winding would be good 4 times as low.
> So
> > the rule of thumb seems very conservative.
> >
> > I have made step-up power converters using these cores and have been
> super
> > impressed how well they work at frequencies well below the rule of
> thumb. I
> > have run 30+ watts through these dinky cores with them just barely
> getting
> > warm.
> >
> > Tim N3QE
> >
> > On Sun, Jul 15, 2018 at 6:29 PM, Chuck Hutton
> > <charlesh3@msn.com<mailto:charlesh3@msn.com>> wrote:
> > The commercially available Beverage transformers I have seen are like the
> > W8JI model: 2 primary turns on a BN73-202 core.
> >
> > My calculations say 4 turns are needed at 630 m.
> >
> >
> > Does anyone know of commercially available transformers with isolated
> > windings that operates well down to 630m?
> >
> >
> > Chuck
> >
> >
> > _________________
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> >
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> >
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