BNC Coax Cable Length Signal Degradation 3ft. vs 5/6 ft.

[Ikaruga11]

So I'm going to order some BNC Cables from RetroAccess today and was wondering if there is any difference in image/audio quality between 3 foot and 5/6 foot cables. 3 feet being the minimum distance I need and 5/6 feet being the maximum distance I need.

[azmun]

I would like to know the answer to this as well. In addition, I'd also like to know if there are there any differences between the SCART coax and BNC coax in terms of quality.

[matt]

You won't notice a difference with cables that short, unless you're using poor quality materials. The main reason is this case would be cable management.

[Sirotaca]

So I'm going to order some BNC Cables from RetroAccess today and was wondering if there is any difference in image/audio quality between 3 foot and 5/6 foot cables. 3 feet being the minimum distance I need and 5/6 feet being the maximum distance I need.

Zero difference. You don't even really need the 75 ohm coax at those lengths.

I would like to know the answer to this as well. In addition, I'd also like to know if there are there any differences between the SCART coax and BNC coax in terms of quality.

Not really. The main advantage of BNC and DE-15 is that they're locking connectors. The reason I switched to DE-15 is that my heavy 75 ohm coax SCART cables had a tendency to work themselves loose from my OSSC's SCART socket and I got tired of dealing with it.

[Ikaruga11]

You won't notice a difference with cables that short, unless you're using poor quality materials. The main reason is this case would be cable management.

Zero difference. You don't even really need the 75 ohm coax at those lengths.

Thanks. When you say cable management, do you mean tucking the cables along edges to hide the cables and make everything look cleaner? That's what I want to do, but it'll mean I need longer cables to do that. Would 7/9/12 ft. cables have any signal degradation?

[maxtherabbit]

No. Using coax you really don't even need to *consider* cable loss until 25' and up

[Dochartaigh]

No. Using coax you really don't even need to *consider* cable loss until 25' and up

And only after 75' I believe if using something like an Extron Switcher (always with quality cable of course .

[NewSchoolBoxer]

Advice is all good but I wanted to be scientific here since asking if 12 ft matters when 3-6 ft does not is a very fair question if you haven't studied transmission line theory. I also want to hit on azmun's question.

Overview

Let's assume vendor uses legit brand Belden cables since Belden has nice datasheets. Let's further assume vendor is using coax that you want and not unshielded garbage to save 10 cents on a 6 ft / 1.8 meter cable. You have DC losses and AC losses to consider that increase linearly with length, meaning losses at 3 ft are double at 6 ft and 10x more at 30 ft. AC loss further increases by the square root of the frequency.

In the NTSC and PAL video signals we care about, the luma (brightness) is amplitude modulated and part of the chroma is too. Meaning more losses will lower the amplitude of the signal and make the video look worse. We can draw two broad conclusions:

-A cable made for 5-6 MHz 480/576i can get away with cheaper materials than 480/576p that has (basically) double the frequency.
-A composite video cable can get away with cheaper materials than, say, RGB since the maximum possible quality is much lower to begin with. Can call this the signal to noise ratio (SNR) and measure in dB.

What matters with high quality cables

DC losses, I'd care about 1 ohm maybe, which takes a cable of 24.1 feet (7.3 meters) to achieve on a datasheet figure of 41.5 ohm/1000 ft and nicely coincides with maxtherabbit's 25 feet. You should consider total cable length, meaning a convoluted device chain using four 6 ft cables is equivalent to 24 feet for 1 ohm of total loss.

The 41.5 figure comes from Belden RGB Video that is 26 AWG stranded copper. AWG is US measure of thickness, with smaller being thicker like piercings.

Its AC loss at 5 MHz we can use for 480/576i video is 1.3 dB/100 ft. Note the 100 feet vs 1000. I care about 0.2 dB when 30 SNR is RGB level and 26 SNR is blurry composite video. So we need a cable length of 15.4 feet (4.7 meters) to hit 0.2 dB loss and the increase from 3 to 6 ft is just 0.039 dB. At 480/576p the loss jumps to about 1.8 dB/100f, dropping the 0.2 dB point to 11.1 ft (3.4 m).

Chain two 6 ft cables together and see if you can notice a drop in video quality. Each cable connection adds further (small) loss from two pins linking. I think you can't tell a difference in quality but at four x 6 ft (1.8 m), I suspect you could. Naturally the quality of the television / monitor matters too, as well as any video processing or filtering it does.

The thing is, SNR is diminishing returns. It's a logarithmic scale. A 27-ish s-video SNR looks much, much better than 26 SNR composite and jumping to 30-ish RGB and Component is not 3x the quality. I say 0.2 dB matters but is somewhat arbitrary and could argue for a slightly different value.

I would like to know the answer to this as well. In addition, I'd also like to know if there are there any differences between the SCART coax and BNC coax in terms of quality.

-Yes, running audio alongside video in SCART gives chance for 50/60 Hz audio buzz by audio crosstalking on video line. Won't happen on high quality cable but then you run into which cable maker has actual high quality and when/if they switched the materials without telling you. What SCART doesn't have is a brand like StarTech or Extron mass producing VGA and BNC cables where quality control is going to be superior.

-The problem with SCART / JP-21 / VGA vs BNC is you're limited in how thick the conductor and shielding can be for each R, G, B and sync line versus running them all separately in BNC. I see 26 AWG as standard in VGA, whereas I expect thicker 20 AWG in BNC. Thicker cables have much lower DC and AC losses, although we're saying that doesn't matter at short distance. Other concern is crosstalk on sync or one video line to another that won't happen in separated BNC. BNC has the highest quality potential but, sure, 26 AWG non-pure copper would be worse.

So what about low quality or paper-thin or non-coax cable?

Thin 28.5 AWG on otherwise fine Belden copper cable has 70.5 ohm DC and 1.85 dB AC losses at 5 MHz, compared to 26 AWG's 41.5 ohm and 1.3 dB above. Cheap steel cladded with copper cable has several times more DC loss than pure copper equivalent so that 24.1 feet (7.3 meters) cutoff can drop to 6 ft (1.8 m).

Paper-thin (cheaper) 30 AWG coax cable using (cheaper) aluminum or cladded steel? You're losing quality at any length. I don't think manufacturers of cables that bad are going to give you a datasheet to prove how bad their cables are though.

Non-coax is going to be very susceptible to electromagnetic interference including crosstalk.

Safe 12-24 ft (3.7-7.6 m) total cable length is only with high quality 26 AWG or thicker copper cables and Dochartaigh makes good point that a low quality switcher can degrade signal too. (Audio cables can be thinner)

[kitty666cats]

If you read the manuals/specs/etc of things like Extron RGB interfaces, their potentiometers for gain/skew/sharpness etc all mention that they are intended for *long* cable runs - fact of the matter is, a lot of the excessive gear we all buy for our ancient low-resolution hardware is intended for locations like stadiums/auditoriums/large outdoor events et al. Unless you live in a (maniac) mansion, probably aren’t going to have to worry about your cabling contained within 1 room unless you actively seek out the absolute cheapest & most iffy-looking shit possible.

All that being said - sometimes the more cost-efficient cables can end up being superior to other more expensive brands. I once tested some cheap CMPLE component cables versus some Monster & Tributaries component cables and the generic-looking CMPLE ones ended up being the best of the bunch. However, Belden being mentioned is relevant. Belden is always a safe bet - super nice cabling & can be found for reasonable prices on eBay if you take a little time. Canare is another “can’t go wrong” as well.

Probably wanna double check and be sure the cables are specified as 75ohm & RG-59… but if your cable run is super-short then even RG-58, 50ohm etc aren’t really a big deal.

https://www.ebay.com/itm/HI-RES-Belden- ... 3074465727

BTW anyone looking for a super nice VGA to BNC should peep this seller’s store - they have a lot of these/pretty reasonable price. Been on my watch list for a hot minute, lol

[azmun]

Yes, running audio alongside video in SCART gives chance for 50/60 Hz audio buzz by audio crosstalking on video line. Won't happen on high quality cable but then you run into which cable maker has actual high quality and when/if they switched the materials without telling you. What SCART doesn't have is a brand like StarTech or Extron mass producing VGA and BNC cables where quality control is going to be superior.

-The problem with SCART / JP-21 / VGA vs BNC is you're limited in how thick the conductor and shielding can be for each R, G, B and sync line versus running them all separately in BNC. I see 26 AWG as standard in VGA, whereas I expect thicker 20 AWG in BNC. Thicker cables have much lower DC and AC losses, although we're saying that doesn't matter at short distance. Other concern is crosstalk on sync or one video line to another that won't happen in separated BNC. BNC has the highest quality potential but, sure, 26 AWG non-pure copper would be worse.

So assuming both are using high quality coax, BNC is still basically the superior terminal. This is in theory but in practice, is there really (high) risk of interference or crosstalk at the end of SCART plug? Also, consider that many of us will still require and use a SCART to BNC breakout cable for inputs to PVMs, does a pure BNC cable still have an edge or make any sense?

Regarding quality VGA cables, should we be skeptical of them? It seems Retro-Access does not believe it is possible given certain limitations. From their blog, "For vga type cabling: This [75 ohm coax] is available, but tends to be a bit of a scam, we’ve found cabling labelled as 75 ohms that can’t possibly be given the physical properties of the cable."

[Ikaruga11]

Definitely interesting stuff. On a somewhat related note, can audio lines cause interference to video quality in cables? I know the reverse can happen with video lines causing interference to audio quality, which manifests as the common analog buzz or humming during silence.

The reason I ask is because I just ordered RGBS CSync coax BNC cables with Phoenix audio lines from Retro Access today, not realizing that every console I bought the cables for would have digital audio output via HDMI thanks to mods, rendering the analog audio pointless. I don't want the audio lines impacting the video quality.

Oh, and I decided to go with 6ft. cables for my consoles for more versatility in my setup and easier cable management (no wires hanging in plain sight like a spider web. neatly tucked and hidden along edges instead). After being fed into an Extron Crosspoint (which helps preserve signal integreity), they're going to be fed into a 9ft. RGBS CSync BNC coax cable with no audio lines.

[NewSchoolBoxer]

Definitely interesting stuff. On a somewhat related note, can audio lines cause interference to video quality in cables? I know the reverse can happen with video lines causing interference to audio quality, which manifests as the common analog buzz or humming during silence.

The reason I ask is because I just ordered RGBS CSync coax BNC cables with Phoenix audio lines from Retro Access today, not realizing that every console I bought the cables for would have digital audio output via HDMI thanks to mods, rendering the analog audio pointless. I don't want the audio lines impacting the video quality.

Oh, and I decided to go with 6ft. cables for my consoles for more versatility in my setup and easier cable management (no wires hanging in plain sight like a spider web. neatly tucked and hidden along edges instead). After being fed into an Extron Crosspoint (which helps preserve signal integreity), they're going to be fed into a 9ft. RGBS CSync BNC coax cable with no audio lines.

Thank you, I want to think I'm not writing to myself. Your setup sounds good and the Extron Crosspoint is an active switcher that helps preserve signal integrity like you're saying. The signal repair can be said to mean you're running effectively 9ft and not 15ft.

Yes, audio can interfere but it's so low frequency that it doesn't mess with video. As in, encoding mono (left + right channels) at horizontal sync ~15 kHz and stereo at double ~31 kHz would give interference at 15, 30 kHz and 45, 60, 75, 90, etc. kHz harmonics. Luma clusters around 1 MHz and higher and isn't going anywhere near 100 kHz. Chroma is all above 3 MHz. Therefore, audio crosstalking on video is invisible from video's point of view. Still invisible if on NTSC and PAL subcarrier due to being above the video bandwidth.

Audio can mess with sync due to sharing the bandwidth but sync is effectively a digital signal and therefore resistant to electromagnetic interference. Sync crosstalking on audio can be a real problem, both from horizontal sync and the famous 50 or 60 Hz vertical sync, not to mention audio cable being thin as a rule. Audio is low power and low frequency so thin cable is justified, unless you're running the same frequencies right next to it.

Voltage regulators in consoles have 50 or 60 Hz hum but the filtering capacitors are supposed to reduce the ripple too much to matter. Aged or dead power filter capacitor then is another possible source of audio buzz and obviously any power cable sitting next to audio.

[NewSchoolBoxer]

So assuming both are using high quality coax, BNC is still basically the superior terminal. This is in theory but in practice, is there really (high) risk of interference or crosstalk at the end of SCART plug? Also, consider that many of us will still require and use a SCART to BNC breakout cable for inputs to PVMs, does a pure BNC cable still have an edge or make any sense?

You bring up a point no one talks about but we should: the end of SCART / JP-21 and any VGA not from a major manufacturer. To add the connector to the cable wiring, you have to strip off all the wire shielding to solder to the the joint and the solder is mostly tin which has 15% the conductivity of copper. BNC can avoid soldering with crimp or compression tool and preserve the braiding. No other wire is directly next to it.

I think the small area exposed is okay at 480/576p and below. Let's say exposed wire length is 2-3% of a 6ft (1.8m) cable. You know what an antenna is? It's a long conductor with no outer shielding that is good at radiating energy (losing voltage) and receiving energy in the form of electromagnetic waves (noise). I think a 2in (5cm) is too short to matter in either case due to low-ish frequencies involved.

The two classic soldering mistakes are cold solder joint and solder bridge. If people test their cables or are pros at making them then I don't think is big deal. If we say cable on multiout to SCART connector has 1 side of solder joints, I wouldn't measure the impact until you get to 4 sides of solder joints in the same chain.

Theoretical

One more reason why BNC is in theory the best: Parasitic capacitance. What does a pair of conductors of changing voltages with a small a gap between them sound like? A capacitor, a paratactic capacitor in parallel. How many pairs? Let's go with RGBS: R-B, R-G, R-S, G-B, G-S, B-S - 6 and parallel capacitance adds. Fortunately, a small capacitance in parallel is a low pass filter and we're in safe low MHz range. The filtering may be irrelevant but there is still power loss and interference.

If you already bought SCART, may as well keep using. I go console -> VGA BNC breakout since two members here sell VGA female multiouts. Issue is finding or making compatible mulitouts unless you're set on Extron BNC matrix. NES just needs adapter since it has female composite out.

Regarding quality VGA cables, should we be skeptical of them? It seems Retro-Access does not believe it is possible given certain limitations. From their blog, "For vga type cabling: This [75 ohm coax] is available, but tends to be a bit of a scam, we’ve found cabling labelled as 75 ohms that can’t possibly be given the physical properties of the cable."

I read the blog. What they say is reasonable but if I buy StarTech, Extron, Monoprice, Belden, other notable brands that advertise as 75 ohm 26 AWG copper coax then I believe that's exactly what I'm getting. I do agree that cable fraud is a thing and I'd be suspicious of a no name seller or a small diameter of a VGA cabling really containing 4x coax lines, especially if they're undercutting on price.

Coax is thicker than normal cable since it has the inner conductor to carry the signal and the outer conductor to carry the current back. The reasoning is the outer conductor's electromagnetic field will mostly cancel out with the inner's and prevent antenna behavior. Thicker cable is less flexible and coax costs more to make since it also needs a dielectric between the conductors and high quality control to be the right characteristic impedance.

Let's price this out. Can find 30 AWG coax cable on Newark I've never ordered from. Scroll down for Belden's 4x conductor each at 30 AWG pure copper - great for RGBS - at effective $18 for 6 ft (1.8m). Add 2-6 connectors + audio and good luck selling for $60 + shipping. The cable has external diameter of 7.874 mm (0.3 inches) and minimum bend radium of 3 inches. Maybe people complain it isn't flexible enough and return?

Let's race to the bottom! Can find Belden non-coax 4x conductor 22 AWG copper for 25 CENTS a foot at $1.50 for 6 ft (1.8 m). The cable has external diameter of 3.683mm (0.145 inches) and minimum bend radius of 1.375 inches, sweet. No AC losses given but can sell SCART for $20 to undercut everyone outside of China.

IRL

Most of my cables with the "Cheapest JP-21" $12 from China carrying RGB, composite video as sync + audio:

Spoiler

Fitting 6 wires in that, paper thin is the only option and no way is coax but wasn't advertised as such to be fair.
Sony wires thinner than I thought and I can't unscrew Nintendo. Retro-Access says not coax. Very possible to make a superior cable.
I need better PS Component to do real BNC vs VGA and JP-21 subbing as SCART testing.