RF signal transmission Q

According to seller, initial offering of this used standard WifI and suffered massively form drop-outs, so much so they ceased selling it.

They have redesigned these 'Ultra Wifi' units to provide much better range & reliability,

How they are achievng this I don't know ..... I can't get a Tech Sheet.

Anything which contains a radio transmitter must be documented. This is a legal requirement. Threaten them with trading standards.

John

Do you want to have a think about what you just said there, Mr. RF designer?

In my experience, cables tend towards a linear drop-off with frequency, as opposed to a 'flat to X, then 6dB/octave'. It makes cable compensators a pain, they have to be piecewise approximations.

Nope. That's how ADSL manages to do the distances it does. Of course its not a perfect transmission line, and there are dielectric losees thant don't help so ultimately there is HF attenuation , but way less than can be accounted fpor by RC losses

In my experience they dint do either. It all depends on the cable. You can smack a pulse down a 100 meters of coax and get a square wave out more or less. If its terminated correctly. If not then yes, it will look like a straight capacitor

It's all there in the theory of transmission lines. Not hard to find

No, it will still look like a transmission line, but there will be reflections. With a repetitive signal, the reflections will add or subtract and produce a standing wave on the line. See VSWR, which is a measure of termination accuracy, as is return loss in the video world.

Indeed.

You can put over 3Gb/s down the same coax, and not much will crawl out of the other end, but just enough. Most video coaxes will carry 3G-SDI for a hundred metres or so. It isn't flat to 3Gb/s, it just isn't so many dB/octave either. It cannot be completely modelled by small Ls and Cs, there is also series resistance which is small and tends to be ignored in a simplistic transmission line theory. For example, the signal wires in SMPTE hybrid cable (SMPTE 311M) have a fairly poorly defined impedance of about 120 Ohms but a series resistance of about 95 Ohms/km. Resistive leakage through the dielectric usually can be ignored.

It is. Some attempt has been made to manufacture them with a defined impedance, and RS-485 and its cousins and Ethernet use terminations, unlike the V24 standards. Certainly, gigabit Ethernet wouldn't work without good terminations and consistent cables.

I know. That's what I was getting at! IIRC, our "RF designer" friend here has frequently mentioned VSWR in various posts, too. No RF designer ever calls it that. The correct term is return loss. Mentioning VSWR marks a person out as a radio ham or a CBer; certainly not an RF guy.

A US company, they may not worry about UK trading standards, I have asked again.

I have never used either term dear boy

Back when I was doing that stuff, VSWR was the term in practice in Marconis.

But I guess designing military radar is as stupid as being a CBer

If it is US, it has a part number and an FCCID and will appear in a Google search on such terms as FCCID.

Paul

Not only that, but if the installer has imported the radio device they are legally responsible for ensuring compliance with UK or EU regulations as appropriate. Compliance requires markings on the device (or documentation if it is too small) to allow such compliance to be verified. A link to a website hosting a declaration of compliance is enough, but that declaration should provide the necessary information.

John

The nice thing about FCCID tracking, is the web site can have pictures of the circuit board. Then you have a chance to vet the product.

Paul