Hi If you are really going to get everything “tight” at RF, solid grounds (properly done) and good shielding (well thought out) are going to do more for you than a lot of messing with circuits. Common mode chokes (outside cores) are way more likely to help than transformers.
That assumes you are after RF. If you have a 60Hz problem (due to the mega power AC welder) you may need to approach things a bit differently. Bob > On Nov 27, 2014, at 4:20 PM, Mark Spencer <[email protected]> wrote: > > Yep. I found a lot of RF related issues appeared to go away when I switched > to double shielded cables, stopped using T connectors for distributing > signals, purchased and used HP distribution amps, terminated un used ports > with 50 ohm loads etc. > > I also found ferrite cores applied on the outside of longer cables to be > helpful as well. (I found it was useful to measure the actual currents > flowing in the cable shields before and after adding the ferrite cores.) > > I still have a couple of issues that occur when I occasionally transmit at > the 300 watt level on VHF but the day to day issues where by WWV on 5 and 10 > Mhz was hard to hear at times due to signal leakage and many low power > transmissions could be counted on to influence a time lab frequency plot are > gone now. > > I expect issues are still there but they are below the detection threshold > for me. My time nuts gear and radio gear are separate but still in the same > house. > > Mark Spencer > > On 2014-11-27, at 1:47 PM, Bob Camp <[email protected]> wrote: > >> Hi >> >> You can also discover interesting things about the transformer it’s self in >> some circuits. They do what they do, but they also bring along a new set of >> issues. Sometimes simpler is better. If you don’t *need* what the >> transformer does, why add more complications ? >> >> If you don’t lift the ground, the transformer isn’t doing much for you >> isolation wise. >> >> If you do lift the ground, you need a lot more than just the transformer to >> make it all work and isolate properly. Once you add all that “stuff” you >> don’t have a simple circuit anymore. >> >> —————— >> >> One example: >> >> The most likely “threat” to your distribution system is a cell or portable >> phone. The beast fires up at random times and spews RF around everywhere. >> That’s the signal you want to isolate and shield against. It’s at some >> frequency between 40 MHz and 6 GHz depending on what it is. What ever you do >> needs to work over that range for isolation / shielding. It also needs to >> pass 10 MHz. Don’t have a phone in sight? How about WiFi, Bluetooth, and RF >> based remote controls …. >> >> Why is it a threat? The RF comes back into your amp and changes bias levels >> / inter modulates with the 10 MHz. Either way, your 10 MHz moves around a >> bit. Is this purely theoretical? Nope, it happens far more often than you’d >> think. I’ve seen it a number of times. >> >> A simple transformer at 10 MHz is not going to retain balance and isolation >> over 40MHz to 6 GHz. Even if it could the coax connector will imbalance it >> pretty badly. No balance = no isolation. >> >> --------------- >> >> Good cables and a passive splitter have their issues, so do logic gates. >> Both have their advantages. More complicated is not always better. >> >> 23 dBm out of a KS box going down to +7 out gives you 16 db of room for >> attenuation. At 3 db for each 2:1 split, that’s 2^5 splits. It’s rare to >> find a need for 32 outputs. You can get 8 outputs at +13 dbm. That’s pretty >> hot for a distribution amp output. >> >> Bob >> >> >>> On Nov 27, 2014, at 2:02 PM, John Miles <[email protected]> wrote: >>> >>> For the most part, you don't want transformer isolation unless you plan on >>> using balanced lines. There are worse things than ground loops out there, >>> and lifting a coax shield away from ground is a great way to find all of >>> them. >>> >>> You definitely don't want 10.7 MHz IF transformers, unless you are just >>> trying to build a thermometer. >>> >>> -- john, KE5FX >>> Miles Design LLC >>> >>>> -----Original Message----- >>>> From: time-nuts [mailto:[email protected]] On Behalf Of Perry >>>> Sandeen via time-nuts >>>> Sent: Wednesday, November 26, 2014 8:08 PM >>>> To: time-nuts >>>> Subject: [time-nuts] 10 MHz Filters >>>> >>>> List, >>>> >>>> >>>> >>>> I have seen on the net a 10 MHz filter using 10.7 IFtransformers but have >>>> no >>>> idea how well they would work for isolation with thenew style Lucent boxes. >>> >>> _______________________________________________ >>> time-nuts mailing list -- [email protected] >>> To unsubscribe, go to >>> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >>> and follow the instructions there. >> >> _______________________________________________ >> time-nuts mailing list -- [email protected] >> To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >> and follow the instructions there. >> > _______________________________________________ > time-nuts mailing list -- [email protected] > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
