Re: [time-nuts] Function of cap to GND in isolation transformer circuit
The way these caps are wired does not isolate DC from the transformer. The purpose is obviously a different one. Two reasons spring to mind: 1. If the caps are wired close to the connector, and Ground means the metal enclosure, then the caps provide RF continuity between cable shield and enclosure. That keeps RF interference out of the circuit. 2. They reduce the common mode signal coupled into the circuit via the parasitic capacitance between the transformer windings. This should help isolation. Cheers Stefan -Ursprüngliche Nachricht- Von: time-nuts-boun...@febo.com [mailto:time-nuts-boun...@febo.com] Im Auftrag von Geoffrey Smith Gesendet: Donnerstag, 22. Juli 2010 06:13 An: Discussion of precise time and frequency measurement; Geoffrey Smith Betreff: Re: [time-nuts] Function of cap to GND in isolation transformer circuit Joop, The cap is isolate any DC from the transformer, The manual for TADD-1 has this iformation at the TAPR site has this manual http://www.tapr.org/~n8ur/TADD-1_Manual.pdf. On Wed, Jul 21st, 2010 at 9:46 PM, Joop l...@xs4all.nl wrote: Hi, I noticed in several circuits that the 10MHz isolation transformer in input and output circuits have a 6.8nF or 10nF capacitor to GND. How necessary is this for suppression of unwanted signals? Is the transformer itself not sufficient? I would expect common mode issues to be a bit worse with the cap in place. The circuit I refer to can be seen here: http://www.uploadarchief.net/files/download/cap2gnd.png The first one is an output as described in the Efratom FRK manual, the second one the input in the TADD-2 manual. Cheers, Joop ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Function of cap to GND in isolation transformer circuit
Hi The cap likely improves the VHF stability of the circuit. Bob On Jul 21, 2010, at 7:46 AM, Joop wrote: Hi, I noticed in several circuits that the 10MHz isolation transformer in input and output circuits have a 6.8nF or 10nF capacitor to GND. How necessary is this for suppression of unwanted signals? Is the transformer itself not sufficient? I would expect common mode issues to be a bit worse with the cap in place. The circuit I refer to can be seen here: http://www.uploadarchief.net/files/download/cap2gnd.png The first one is an output as described in the Efratom FRK manual, the second one the input in the TADD-2 manual. Cheers, Joop ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Function of cap to GND in isolation transformer circuit
Its to prevent 'earth loops' and avoid issues with DC and low frequency AC on the coax screen - usually its found only on tx or rx end- not both- depends on the installation which practice is followed. Telcos tend to solid ground at the send end and cap ground at the rx end. And yes- it can make things worse-again depending on the installation. If you have the option of hard ground or cap ground at both ends you can select which combination gives the best result. This is usually only an issue with long runs of coax cable. DaveB, NZ - Original Message - From: Joop l...@xs4all.nl To: Joop l...@xs4all.nl Cc: time-nuts@febo.com Sent: Wednesday, July 21, 2010 11:46 PM Subject: [time-nuts] Function of cap to GND in isolation transformer circuit Hi, I noticed in several circuits that the 10MHz isolation transformer in input and output circuits have a 6.8nF or 10nF capacitor to GND. How necessary is this for suppression of unwanted signals? Is the transformer itself not sufficient? I would expect common mode issues to be a bit worse with the cap in place. The circuit I refer to can be seen here: http://www.uploadarchief.net/files/download/cap2gnd.png The first one is an output as described in the Efratom FRK manual, the second one the input in the TADD-2 manual. Cheers, Joop ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Function of cap to GND in isolation transformer circuit
Joop, The cap is isolate any DC from the transformer, The manual for TADD-1 has this iformation at the TAPR site has this manual http://www.tapr.org/~n8ur/TADD-1_Manual.pdf. On Wed, Jul 21st, 2010 at 9:46 PM, Joop l...@xs4all.nl wrote: Hi, I noticed in several circuits that the 10MHz isolation transformer in input and output circuits have a 6.8nF or 10nF capacitor to GND. How necessary is this for suppression of unwanted signals? Is the transformer itself not sufficient? I would expect common mode issues to be a bit worse with the cap in place. The circuit I refer to can be seen here: http://www.uploadarchief.net/files/download/cap2gnd.png The first one is an output as described in the Efratom FRK manual, the second one the input in the TADD-2 manual. Cheers, Joop ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
