0
\$\begingroup\$

If a directional coupler is labeled 5-1002 Mhz, what happens to frequencies above that? Is that just the rated frequencies but above that may work fine, or does that mean it blocks everything above that, or what?

Is there any disadvantage to using a directional coupler with a wider frequency range than I need? So if I need 1.8Ghz today, any reason not to install one rated to 3Ghz so I don't have to replace them again?

Why is it so hard to find vertical F-connector directional couplers above 1.2Ghz?

I'm trying to run some signals through my coax cable above 1002 Mhz, but I have a bunch of directional couplers labeled 5-1002 Mhz and I don't know enough about directional couplers to know if I may or will have to replace them, and what to best replace them with.

MoCA D band adapters use 1125-1675 Mhz. DOCSIS 3.1 & 4.0 go up to 1794 Mhz.

Picture a 100' run of RG6 with a directional coupler every 10', each with a different value. I would like to find identical replacements, just with a higher frequency range. Picture of one of them:

BDC1112V

It looks like Amphenol makes these now: https://www.amphenolbroadband.com/product-category/directional-couplers/ and I found a datasheet, but it doesn't say anything about higher frequencies: https://1ti6799dxp3ds3.bam.zone/public/0daf7f61bac1841a9b83d01fa1e45447

\$\endgroup\$
5
  • 1
    \$\begingroup\$ As with any device, the data sheet is the best source of information about its performance. Undoubtedly, your couplers will work above their rated frequency but performance will suffer. Only you can determine whether that performance is sufficient. \$\endgroup\$
    – Barry
    Aug 26, 2023 at 21:35
  • \$\begingroup\$ Pascal, devices are specified within a range. You'll have to live with a device not being designed for a frequency range not having specification of what it does there. \$\endgroup\$ Aug 26, 2023 at 21:57
  • \$\begingroup\$ If you really want to use a device outside the performance specified in it's data sheet, you can 1) create a source control drawing (SCD) that specifies the performance you need and that the vendor is willing to sign up for (expensive), or 2) test the device over the frequency range you need. \$\endgroup\$
    – SteveSh
    Aug 26, 2023 at 23:49
  • \$\begingroup\$ What would I use to test it? \$\endgroup\$
    – Pascal
    Aug 27, 2023 at 23:35
  • \$\begingroup\$ We would use a network analyzer of some sort, as we have many of them on site. Or a signal generator and 'scope or spectrum analyzer. \$\endgroup\$
    – SteveSh
    Aug 28, 2023 at 0:20

2 Answers 2

1
\$\begingroup\$

Is that just the rated frequencies but above that may work fine, or does that mean it blocks everything above that, or what?

Or what. Anything might happen; directivity/isolation might (will, probably) suffer, so will insertion loss and reflections.

That's the case for any operational specs: once you leave the specified operational range, the device makes no guarantees anymore.

Is there any disadvantage to using a directional coupler with a wider frequency range than I need?
So if I need 1.8Ghz today, any reason not to install one rated to 3Ghz so I don't have to replace them again?

As long as your other needs (price, isolation, loss) are still met: no

Why is it so hard to find vertical F-connector directional couplers above 1.2Ghz?

Because F-Connector is something that's indicative of low-tech building installation for TV purposes, not for higher microwave frequencies. It's usually used with RG-59 cabling (which at 1 GHz commonly already has ~ 25 dB attenuation over 100 m, and rarely is specified for frequencies above 1.5 GHz at all) or RG-6 (which is a bit better, at least being often specified to 2.3 GHz, but there with losses above 30 dB / 100 m). The connector is an inaccurate mess and will leave you with multiple digits of attenuations at 3 GHz – so nobody sensible would produce a product for these frequencies and equip it with an F-Connector.

DOCSIS 3.1 & 4.0 go up to 1794 MHz.

That's true, but don't expect the higher end of that band to have the same SNR at the CPE as the lower end; also, the upling only goes up to (if my memory serves me right) 208 MHz, so the directivity needs for higher frequencies are asymmetrically "sharp"; the upstream simply doesn't care about crosstalk above 208 MHz.

Also, I'm still pretty bitter that F Connector was the coaxial connector that would inherit the role of Belling-Lee in Europe; what an annoying choice. But what is customer satisfaction when you can save 10 ct per connector compared to say TNC or BNC? That would have solved the bandwidth problem for much longer than introducing F connectors when cable TV became a thing in Europe.

\$\endgroup\$
2
  • \$\begingroup\$ In addition to cost, the key benefit of F series is how easy they are to fit. I use SMA and BNC a lot, with N, TNC, and MCX for specials, but for quick wiring of TVs, F is hard to beat. \$\endgroup\$
    – colintd
    Aug 26, 2023 at 22:59
  • 1
    \$\begingroup\$ Agreed, but my guess is that the number of new residential installations that get pure one-way TV and aren't expected to, somewhen in the next two decades, want internet at fight frequencies, isn't that large \$\endgroup\$ Aug 26, 2023 at 23:16
0
\$\begingroup\$

If a directional coupler is labeled 5-1002 Mhz, what happens to frequencies above that? Is that just the rated frequencies but above that may work fine

It may work fine, but I doubt it. If the coupler worked fine at higher or lower frequencies, the manufacturer would advertise that.

does that mean it blocks everything above that, or what?

A directional coupler has no active components, and to prevent unnecessary losses, contains no intentional resistances other than the 4th port termination. It is therefore unlikely that one would suddenly get no output. More likely the amplitude at the output(s) would decrease if used as a splitter, or there would be coupling between the inputs if used to combine inputs.

Picture a 100' run of RG6 with a directional coupler every 10'

Your signal will be horribly attenuated at the end of this 100' run.

I don't know enough about directional couplers to know if I may or will have to replace them, and what to best replace them with.

If you are coupling or splitting signals, then if you replace them, you will need to replace them with other directional couplers.

However, it may be that the directional couplers were merely used originally for convenience, to connect smaller lengths of cable. If that is their sole purpose, then they should definitely be replaced with simple female-to-female straight through connectors. Directional couplers should only be used where needed, to avoid unnecessary signal attenuation.

enter image description here

www.showmecables.com

\$\endgroup\$
2
  • \$\begingroup\$ A directional coupler every 10-20' along a coax run inside buildings is common around here. Each tap goes to a different hotel room/apartment/classroom/office/whatever. Outdoors the directional couplers may be 50-100' apart, with the taps going to different houses. The former is often called SMATV, the latter CATV. The point of a directional coupler instead of a splitter is to prevent the signal on the trunk from degrading too much. \$\endgroup\$
    – Pascal
    Aug 26, 2023 at 22:39
  • \$\begingroup\$ @Pascal Since the couplers are actually used for splitting the signal, they cannot be avoided. But this surely means that the signal must be significantly amplified before being routed through the cable system. \$\endgroup\$ Aug 26, 2023 at 22:42

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.