antenna cable attenuation measurement

[humbuk]

How can the attenuation on an antenna cable be measured? Thanks

[fieldsound]

A few options:

1) look at the chart for the specific antenna cable you are deploying, ie RG8x, LMR240 etc. Each of these cable manufacturers publish charts with precise attenuation specs for the given frequency you are working with.

 

2) Several websites exist with calculators for this purpose. Here is a handy one from Times Microwave.

https://timesmicrowave.com/calculator/

3) use a tool such as BSRF power meter for a quick readout of attenuation. 

https://www.bs-rf.com/en/products/rf-power-meter/

 

 

[Wyatt Tuzo]

Get yourself a Vector Network Analyzer (VNA). Not terribly expensive, and well worth having in the kit for testing purposes. 

[Derek H]

Yeah, I’d second Wyatt’s suggestion. It’s also useful for testing antenna setups. 
 

Wyatt, I assume you’re talking about the nanoVNA? That’s the one I have. It’s definitely not user friendly since it’s an actual scientific measurement tool but it’s cool what it can do. Also, it’s cheap. 
 

Also worth noting here the new Betso octopus RF distro has some kind of way to give you a loss measurement for testing your cables. 

[Constantin]

Depending on how precise you need it, knowing that’s very roughly 1dB loss for every 3 meters of cable length might be all you need

[Derek H]

Yes the normal way we’ve all been doing it is to just look up the loss/foot of your cable type and do the math. 
 

But I do like having the NanoVNA now to test cables and verify expected specs. 

[Wyatt Tuzo]

On 12/6/2024 at 7:21 PM, Derek H said:

Yeah, I’d second Wyatt’s suggestion. It’s also useful for testing antenna setups. 
 

Wyatt, I assume you’re talking about the nanoVNA? That’s the one I have. It’s definitely not user friendly since it’s an actual scientific measurement tool but it’s cool what it can do. Also, it’s cheap. 
 

Also worth noting here the new Betso octopus RF distro has some kind of way to give you a loss measurement for testing your cables. 

The Octopus looks super intriguing!

 

But yes, the NanoVNA will do nicely with very little investment. 
One benefit of going this route is you can easily measure end-to-end loss through devices, any interconnected cables, splitters, barrels, etc.

 

While it can get more complicated (measuring phase, etc), I usually just pay attention to the attenuation trace. 

[Derek H]

Yes, it can do much more than we would generally be interested in, Smith chart for example. You do have to be careful with the settings and calibration to be sure you’re getting good data but I love it. 
 

I’ve used it to measure SWR of my antennas to gauge that they’re working correctly. I confirmed a bad Comtek phaseright this way. Of course, you could also determine this the normal way by the fact that it’s working like shit but it’s nice to be able to dig a little deeper and check all the components. 
 

The other nice thing about measuring antenna cable loss with the nanoVNA is that it plots the data across a specified frequency range so you can easily see what the loss is for your target frequencies. For example, a cable that has 12dB of loss at 600MHz might only be about 6dB at 200MHz or on the other end maybe more like 16dB at 900MHz. 
 

The fact that you can do all this with reasonable accuracy on a <$100 device is amazing.

[Conor]

All you need for that is the calculator, or to look at the cable datasheet.

 

That being said, +1 for the nanoVNA. Being able to measure the effectiveness of your antennas over frequency is very useful.

[humbuk]

Thanks for the advice, I finally figured out a way to do it from things I already have :). I didn't measure the attenuation exactly, but I was more interested in comparing some cables with each other and whether there was a bad one... I used the RF explorer and a bodypack transmitter. I connected the measured cable to the RF explorer and connected the antenna output of the transmitter to its end and measured the cables with each other like this...

[Derek H]

Careful you don’t blow up your RF Explorer front end connecting it directly to a transmitter. Not sure what the max signal input is. May want to at least start with the lowest transmitter power. Good thinking though!

[henrimic]

https://www.betso.eu/rf-octopus

 

This appealing new product can also measure cable loss .... but not only.

[ivanovich]

tone generator & oscilloscope combo?

 

[humbuk]

On 12/13/2024 at 1:33 PM, henrimic said:

https://www.betso.eu/rf-octopus

 

This appealing new product can also measure cable loss .... but not only.

Yes, this product was actually the impetus for me to start looking for it. I thought to myself, if such a feature can be an add-on in such a small box, it must be easy and cheap :).

[Constantin]

On 12/15/2024 at 2:00 PM, humbuk said:

 in such a small box, it must be easy and cheap :).

Yeah, because small things are always easy and cheap…

[humbuk]

12 minutes ago, Constantin said:

Yeah, because small things are always easy and cheap…

joke - that's why there's the smiley face

[Neil Mc]

On 12/13/2024 at 9:03 AM, henrimic said:

https://www.betso.eu/rf-octopus

 

This appealing new product can also measure cable loss .... but not only.

This looks like a  beautiful little machine for the RF obsessed mind.