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 <charle...@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 <tsho...@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 <charle...@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 <kd...@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-boun...@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 <tsho...@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.sm...@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 > > <charle...@msn.com<mailto:charle...@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 > > > > > > _________________ > > Topband Reflector Archives - http://www.contesting.com/_topband > > > > _________________ > > Topband Reflector Archives - http://www.contesting.com/_topband > > > > > > --- > > This email has been checked for viruses by AVG. > > https://www.avg.com > > > > _________________ > > Topband Reflector Archives - http://www.contesting.com/_topband > _________________ > Topband Reflector Archives - http://www.contesting.com/_topband > _________________ Topband Reflector Archives - http://www.contesting.com/_topband