Hi DF96,
I do use RCA plugs for audio interconnection and nothing else.
-Chris
I see RCA connectors inside consumer equipment, like old TVs for the UHF tuner signal output. They are often soldered to the UHF tuner chassis. That is an application where the impedance is supposed to be 75R.
I do use RCA plugs for audio interconnection and nothing else.
Then you must know what connector it is, and the operating impedance at RF frequencies.
Okay, so then what is it? You are disputing my claim that some RCA connectors are 75R, I would expect you to have some reference to go by. My life's work points to RCA being used in 75R environments, and that satisfies the "some" part of my statement. I would be correct in that case. I did state that I don't know if there is any application other than 75R. Of course low frequencies don't count as the systems are highly variable in operating impedance levels. The wavelength is so long that it doesn't matter.
-Chris
No. I have no objections against RG-174. RG-179 might have lower capacitance, but I have not checked this.
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Beautiful work Damir! I see you used isolated RCAs? I'm glad for you that you live in an environment where you can get away with doing that!
In my experience which is largely audio production, isolated RCA inputs can cut down crosstalk, but in a high RF environment they can allow trash into the box. Indeed in an industrial setting I found it highly advantageous to use transformers at inputs to truly balance the transmission line to let it do it's common-mode cancellation thing, it is a magic fix! In other units I found it worked well to employ 600 ohm terminations to lower the impedance which greatly reduced the RF amplitude. I often still had to bypass XLR pins 2 & 3 to the chassis right at the connector with 0.001uF micas to truly control RF input, especially when high power RF fields are encountered as when a dielectric sealer (20KW@27MHz) is in operation. Most likely this just showed the degree of imbalance in those systems. If your system is working well in your environment, then kudos! The fewer the devices in the path the better.
Many recording facilities are located by necessity in urban areas with high RF fields. One RF survey I had done recently at a proposed site showed there was over 2V/M (>126 dBuV) peak RF from 50 MHz to 6 GHz! I have modified my approach to RF control these days where customer's budgets can take it: I advocate for Faraday shielding of audio facilities with multi-stage main panel AC power filtering; the combination has proven highly effective at cleaning up recording environments. This allows musicians to use all of their poorly designed toys with impunity, like the poorly shielded high impedance single-coil guitar pickups which have plagued recordings with noise since the dawn of recording. There are so many other musical instrument setups which have really poor RF immunity, but have a specific characteristic that a musician will not trade, not to mention processing equipment of questionable lineage, some of which have unbalanced inputs or outputs...yet use XLRs to look professional.
I need to get back building. I wish I had one of the many devices I built at AMI to embarrass myself here with...I was specifically proud of the monitoring units I built for the QC and transfer rooms with Shallco stepped attenuators so operators could give us in engineering an accurate dB measurement of gain issues in production. It had a remote which allowed the operator to sit in the sweet spot of the near-field monitors and switch between source and transfer for confidence... Although I must admit it was all XLR balanced ins and outs and full of 5534s and some Jensen transformers, not balanced FET topology as the geniuses here like you do so well...
Sorry to blather on, back to you.
Cheers!
Howie
Is that different from the BNC case? Combining a 75R BNC plug with a 50R BNC socket results in .......
As i´ve never seen a real standard for "RCA" i´d say that a socket that is compatible with every RCA plug can be called a "RCA socket" and otoh a plug that is compatible with every RCA socket can be called a "RCA plug".
Both in the sense that a stable signal transmission is possible.
The nextgen design actually does give a 75 ohm connector through impedance. It does so by design of the shield path. So, no it is not a 30'ish connector with a matching network, but a true match. Unfortunately, using a standard female ruins the through impedance.
As a side note, by splitting the shield path as they did, they produce an entry path for rf. It's better to change the dielectric material to one with the correct blend of permittivity and permeability, permeability done without dissipation and linear within the range of fields. Like what they did with microwave lenses back 50 years or so.
It's that, or get some dielectric with relative permittivity below 1.
jn
Thanks Howie,
RCA are isolated but the ground is connected to the chassis via XLR connectors, pin 1 grounded. Is it this good approach?
BR Damir
What Pavel said. Worst case is bringing all input grounds to the PCB, then to a remote chassis ground. XLR pin 1 must be grounded at the chassis where it is mounted and RCAs should be directly grounded to the chassis. In the past I have put a piece of PCB inside the chassis that the RCAs ground to and which serves as the reference ground for the unit. In a high RF environment where bypassing is also indicated the capacitors are tied directly from the connector to this ground plane. In cases where the RCAs come already isolated from the chassis I have also modified equipment to have their isolated jack shells bypassed to the chassis with a small capacitance to kill the RF intrusion on the ground lead.
Any true broadcast product is designed to operate properly in an environment with high RF levels and will have measures like these designed in. When one is building components for home use requirements for RF control are less stringent. However, as we are finding out in the studio business, between cell phones, Bluetooth and WiFi devices, local RF near equipment can be quite high in the 600MHz-5GHz spectrum. We have had to fix multiple cases of random "clicks and buzzes" which turned out to be due to these sources coupled with poorly designed pro or semi-pro studio equipment.
Cheers,
Howie
Hi 20to20,
I mentioned that major manufacturers had used RCA connectors in UHF applications. It wasn't me, I only reported on the sightings. Also, what in the world would an F-type RCA connector be? The F connector threads onto the female whereas the RCA connector is a friction fit connector. Two completely different types of connectors.
This isn't your first "off" post. Try to be more considerate to your fellow members here. I'm reasonably certain that most have a great deal more experience than you do judging from your comments.
I was wondering if the characteristic impedance of your garden variety RCA connector wasn't close to 75R. The old ones, not the very inexpensive types that flood the market today.
I recently bought a pile of RCA plugs from a major US manufacturer. The reason I did this was because I knew the dimensions will be correct, and they are very robust. They cost a lot more than the Ebay types you can buy. A basic plug, no gold, no colour keying and no fancy features. Just a good plug. No F plug characteristics at all.
-Chris
Ahhh, no. Give your head a shake before responding to posts and try to think first.
I mentioned that major manufacturers had used RCA connectors in UHF applications. It wasn't me, I only reported on the sightings. Also, what in the world would an F-type RCA connector be? The F connector threads onto the female whereas the RCA connector is a friction fit connector. Two completely different types of connectors.
This isn't your first "off" post. Try to be more considerate to your fellow members here. I'm reasonably certain that most have a great deal more experience than you do judging from your comments.
I was wondering if the characteristic impedance of your garden variety RCA connector wasn't close to 75R. The old ones, not the very inexpensive types that flood the market today.
I recently bought a pile of RCA plugs from a major US manufacturer. The reason I did this was because I knew the dimensions will be correct, and they are very robust. They cost a lot more than the Ebay types you can buy. A basic plug, no gold, no colour keying and no fancy features. Just a good plug. No F plug characteristics at all.
-Chris
Actually, you make an interesting point, 20to20. I have always been confused with the 'smooth' F connector and an RCA. I guess it is just the 'male' that is really similar, but it is confusing. I would have to look carefully as to how they achieve 75 ohms, where no NORMAL RCA connector will.
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That was my point, a 75 ohm F connector for typical VHF coax antenna input isn't called an RCA jack. In your earlier post you seem to be confusing UHF impedance matching with VHF impedance matching with RCA connector impedance matching. Your reference to UHF tuner output via RCA plug connectors as being 75R, doesn't take into consideration that the tuner has done the demodulation and is outputing composite signal that can be carried OK with standard cable with an RCA plug and jack. The connector itself is not the determinant of the impedance rating of the circuit, the input to the following amps is. You can put an RCA connector on a 75R coax cable but its not the connector that makes it 75R. So there really is no 75R RCA to ponder.
Yes, it's the cable rating (what impedance) and what its purpose is (feeds what impedance?) that is important. I have used adapters to connect 75R F-connector terminated coax to RCA jacks to make long low loss audio cables but that didn't convert the impedances in or out. No matching transformers necessary for that application.
Yes, with that modulator in a device generating the video the other end of that RCA plug on a 75R cable would likely have a female F-connector on the other end for an output connection for a coax to TV channel 3-4 VHF input. And everyone's happy. The technician doesn't have to solder/unsolder the cable to swap out a failed unit.
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Those are designed for 75R coax termination. Is that what the discussion was about, do RCA phono connectors for coax cable exist? ?? .....yes.
As stated in my first post on this topic i´ve mentioned that other manufacturers are labeling their RCA´s as 75R connectors, but that i had my doubts when looking at the pictures.
It seems that it indeed is more a terminology to point to compatibility to 75R coax cables considering diameters and crimping style not to the actual characteristic impedance of the connector itsself.
But, the mentioned WBT RCA combo does realize a 75R characteristic impedance, but - as jneutron already pointed out - compromises the shield effiency to reach their goal.
@ anatech,
last time i calculated (long time ago) it the impedance was more in the 30R to 40R region, depending on the specific diameters and dielectrica used in the various RCA types.
I suppose the whole Nextgen thing was triggered by the success of the "Eichmann" plugs and therefore had to be mainly constructed by using "less metal" .Looking at the construction and the number of different parts coming together i´d think that the tooling costs were quite high and manufacturing is imo still done in germany, but of course the consumer price surely includes sort of "high end audio" luxury mark-up.
What a pity....
Considering the sale figure, i obviously don´t know, but looking at the catalog of Canare and the mentioned Pasternack, and their quite large number of variants that their must be much higher demand than i´d have expected.
Could be that there is even more interest if it is a true 75R connection.
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