On 08/05/2019 12:15 am, John Larkin wrote:> On Tue, 7 May 2019 21:55:54 -0000 (UTC), Cursitor Doom > <curd@notformail.com> wrote: > >> On Tue, 07 May 2019 15:28:27 -0400, Phil Hobbs wrote: >> >>> On the 2 pF scale, once it's warmed up and zeroed it'll sit there >>> reading 0.000 pF all afternoon. Wave your hand nearby and it'll read a >>> few femtofarads and then back to zero. Really a good gizmo. >> >> What methodology are they using to measure these very low capacitances? > > There are manuals online, with schematics. > > Basically they apply a 1 MHz sine (sometimes other freqs on different > models) to one end of the cap and measure the current on the other > end, with RF circuits and amps and a phase-sensitive detector. Lots of > RF gain gives sensitivity. > > > >The Boonton 72 measures the capacitance between the two test terminals while rejecting stray capacitance to ground which is neat. I only need to use it once or twice a year but it is unbeatable. piglet
Tuned Circuit Selectivity
Started by ●May 5, 2019
Reply by ●May 9, 20192019-05-09
Reply by ●May 9, 20192019-05-09
On Thu, 9 May 2019 09:23:14 +0100, piglet <erichpwagner@hotmail.com> wrote:>On 08/05/2019 12:15 am, John Larkin wrote: >> On Tue, 7 May 2019 21:55:54 -0000 (UTC), Cursitor Doom >> <curd@notformail.com> wrote: >> >>> On Tue, 07 May 2019 15:28:27 -0400, Phil Hobbs wrote: >>> >>>> On the 2 pF scale, once it's warmed up and zeroed it'll sit there >>>> reading 0.000 pF all afternoon. Wave your hand nearby and it'll read a >>>> few femtofarads and then back to zero. Really a good gizmo. >>> >>> What methodology are they using to measure these very low capacitances? >> >> There are manuals online, with schematics. >> >> Basically they apply a 1 MHz sine (sometimes other freqs on different >> models) to one end of the cap and measure the current on the other >> end, with RF circuits and amps and a phase-sensitive detector. Lots of >> RF gain gives sensitivity. >> >> >> >> > >The Boonton 72 measures the capacitance between the two test terminals >while rejecting stray capacitance to ground which is neat. > >I only need to use it once or twice a year but it is unbeatable. > >pigletIt's great for semiconductor C-V curves. -- John Larkin Highland Technology, Inc lunatic fringe electronics
Reply by ●May 9, 20192019-05-09
On 5/8/19 8:40 PM, Dave Platt wrote:> In article <qavo1n$f13$1@dont-email.me>, John S <Sophi.2@invalid.org> wrote: > >>>> https://blog.aa6e.net/2009/10/my-new-boonton-model-59-gdo.html >>> >>> Well, *if* that isn't the one I have it's identical in appearance at >>> least. I'll have to get it out properly for comparison purposes and have >>> a play with it this weekend coming. >>> >>> Thanks, Phil. >> >> >> DON'T throw it away! I'll buy it for a reasonable price. > > Darned right. > > A few years ago I did a bake-off between several dipmeter I own or > could borrow: my Model 59, a B&W 600 (tube), a Heathkit solid state > (the 1250 I think) and their HM-10 tunnel-diode dipper, and the "dip > meter" plug-in coils for an MFJ 1259. The "test subject" was a > section of Airdux inductor, wired to an air-variable > capacitor... should be a nice high-Q resonator. > > The goal was to see how far away from the test coil I could hold the > dipmeter probe-coil, and still get a readable "dip" at the resonant > frequency. The further away, the less coupling and "pulling". > > The MJF coils were essentially useless... couldn't get a meaningful > dip unless the coil was touching the test coil, or nearly so, and it > wasn't particularly stable or easy to read. > > The HM-10 was almost as bad. > > The Heathkit 1250 could get a dip from an inch or two away. > > The B&W did a bit better than the 1250. > > The Model 59 was getting a detectable dip from 4-5" away. Very, very > good sensitivity. > > I'd love to test one of the Millen GDOs but the only times I've seen > one in decent condition, for sale with its various coils, the price > being asked has made me back away slowly. > > > > >I have one of those too, but I've never turned it on. I'll give it a try when I have a chance. Cheers Phil Hobbs -- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC / Hobbs ElectroOptics Optics, Electro-optics, Photonics, Analog Electronics Briarcliff Manor NY 10510 http://electrooptical.net http://hobbs-eo.com
Reply by ●May 9, 20192019-05-09
On 5/9/19 4:19 AM, piglet wrote:> On 09/05/2019 12:17 am, John S wrote: >> On 5/7/2019 5:06 PM, Cursitor Doom wrote: >>> On Tue, 07 May 2019 15:30:20 -0400, Phil Hobbs wrote: >>> >>>> If it's a Model 59, it's a beautiful thing. >>>> >>>> https://blog.aa6e.net/2009/10/my-new-boonton-model-59-gdo.html >>> >>> Well, *if* that isn't the one I have it's identical in appearance at >>> least. I'll have to get it out properly for comparison purposes and have >>> a play with it this weekend coming. >>> >>> Thanks, Phil. >> >> >> DON'T throw it away! I'll buy it for a reasonable price. >> > > Would $3,900 be reasonable? An Ebay seller is offering a set with the LF > and MF heads as well as the more common HF/VHF head. > > pigletI paid $135 for one of the HF/VHF and $120 for the UHF one. They work perfectly. Cheers Phil -- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC / Hobbs ElectroOptics Optics, Electro-optics, Photonics, Analog Electronics Briarcliff Manor NY 10510 http://electrooptical.net http://hobbs-eo.com
Reply by ●May 9, 20192019-05-09
On 5/9/19 12:30 PM, Phil Hobbs wrote:> On 5/8/19 8:40 PM, Dave Platt wrote: >> In article <qavo1n$f13$1@dont-email.me>, John S <Sophi.2@invalid.org> >> wrote: >> >>>>> https://blog.aa6e.net/2009/10/my-new-boonton-model-59-gdo.html >>>> >>>> Well, *if* that isn't the one I have it's identical in appearance at >>>> least. I'll have to get it out properly for comparison purposes and >>>> have >>>> a play with it this weekend coming. >>>> >>>> Thanks, Phil. >>> >>> >>> DON'T throw it away! I'll buy it for a reasonable price. >> >> Darned right. >> >> A few years ago I did a bake-off between several dipmeter I own or >> could borrow: my Model 59, a B&W 600 (tube), a Heathkit solid state >> (the 1250 I think) and their HM-10 tunnel-diode dipper, and the "dip >> meter" plug-in coils for an MFJ 1259. The "test subject" was a >> section of Airdux inductor, wired to an air-variable >> capacitor... should be a nice high-Q resonator. >> >> The goal was to see how far away from the test coil I could hold the >> dipmeter probe-coil, and still get a readable "dip" at the resonant >> frequency. The further away, the less coupling and "pulling". >> >> The MJF coils were essentially useless... couldn't get a meaningful >> dip unless the coil was touching the test coil, or nearly so, and it >> wasn't particularly stable or easy to read. >> >> The HM-10 was almost as bad. >> >> The Heathkit 1250 could get a dip from an inch or two away. >> >> The B&W did a bit better than the 1250. >> >> The Model 59 was getting a detectable dip from 4-5" away. Very, very >> good sensitivity. >> >> I'd love to test one of the Millen GDOs but the only times I've seen >> one in decent condition, for sale with its various coils, the price >> being asked has made me back away slowly. >> >> >> >> >> > I have one of those too, but I've never turned it on. I'll give it a > try when I have a chance. >I paid $81 for it with a complete set of coils. Cheers Phil Hobbs -- Dr Philip C D Hobbs Principal Consultant ElectroOptical Innovations LLC / Hobbs ElectroOptics Optics, Electro-optics, Photonics, Analog Electronics Briarcliff Manor NY 10510 http://electrooptical.net http://hobbs-eo.com
Reply by ●May 9, 20192019-05-09
On Wed, 08 May 2019 18:17:22 -0500, John S wrote:> DON'T throw it away! I'll buy it for a reasonable price.What on earth makes you think I'd throw it away?? I've had a chance to examine it further today and it's the same as Phil posted about, Model 59 with the pluggable coil set, mint condition, amazingly. No plans to sell it for the foreseeable future. Don't need the money. Got money, want time. -- This message may be freely reproduced without limit or charge only via the Usenet protocol. Reproduction in whole or part through other protocols, whether for profit or not, is conditional upon a charge of GBP10.00 per reproduction. Publication in this manner via non-Usenet protocols constitutes acceptance of this condition.
Reply by ●May 9, 20192019-05-09
On Thu, 09 May 2019 09:19:10 +0100, piglet wrote:> Would $3,900 be reasonable? An Ebay seller is offering a set with the LF > and MF heads as well as the more common HF/VHF head. > > pigletSeems a fair price to me. If we were living in 2040, that is. Some people are just plain greedy. -- This message may be freely reproduced without limit or charge only via the Usenet protocol. Reproduction in whole or part through other protocols, whether for profit or not, is conditional upon a charge of GBP10.00 per reproduction. Publication in this manner via non-Usenet protocols constitutes acceptance of this condition.
