Odd adaptor. What is it?

[ppppenguin]

I found this odd adaptor in a box of stuff. Phono male, F female. About 90mm long.

Measurements:
Phono pin to case: 760R
F pin to case: 82R
Phono pin to F pin: 680R

Nothing obviously L or C as a video signal wasn't distorted when passing through it.

Any ideas?

[Refugee]

It just looks home made to me.

[ppppenguin]

That may be the photo. Definitely a commercial product. There was once a label stuck round it. You can see the remains of the glue.

[Mike Watterson]

Some TV tuners and cable modem tuners inside gear used phono/RCA connector. USA TV and almost all cable TV (maybe not in UK, but Ireland & Continental Europe) uses F-connectors. Obviously an attenuator, though the phono end termination suggests phono socket is about 390 Ohms, which is odd, or the 760R was lower originally.

Certainly straight F to RCA adaptors are still available, though the resistances on that one are odd. I also have RCA-BNC, F-Belling Lee, F-BNC and two sizes of connect adaptors like F but smaller (I think one is 50 Ohm for mobile phone systems).

There are plenty of badly made adaptors, like Y splitter/combiner for Belling Lee TV plugs that have no hybrid, the two sockets and the plug simply wired direct, so it could simply be a badly designed F-RCA attenuator where they only cared about the cable being approximately correctly terminated. The longer than normal thread on the F end suggests it was panel mounted.

[ppppenguin]

Whoever decided to use phono plugs for video should be taken out and shot. It's a mediocre connector for any purpose but its use for video should be banned on pain of death by a thousand pixels. Fortunately I have plenty of phono-BNC adaptors. Both directions. The F connector is a lot better than it looks. A decent, reliable and low-cost connector for aerials. A lot better than the Belling-Lee that's standard in the UK.

My little device is certainly an attenuator. Roughly 75R presented to the F end. A few hundred ohms at the phono end.

[PerdioPal]

The few hundred ohms on the RCA side wouldn't matter for the short distance to whatever it was plugged into, the 75 quite important for the cable, guessing it was used at the "box" end but just one more resistor to make it better? I agree that the RCA connector was/is the worst co-axial connector ever conceived, nearly as bad as the PL/SO239.

[ppppenguin]

The PL259 plug isn't too bad if you can get a decent crimp version. The BBC used a crimp adaptor for the braid that screwed into the back of the standard plug. They were rugged and well regarded in TV broadcasting, especially for OBs. The BNC was a bit vulnerable by comparison. The common variety with reducers were truly evil. Impossible to wire them well.

[Refugee]

The scraped off label made me think home made/modified.