Coaxial cable for BT

[pkaras]

I want to test BT over long range (>1km). I am looking for a flexible 50 cm coax cable to connect transreceiver to antenna. RG316 seems to be the best fit. RG405 would be even better, but it is semi-rugged. Is there any flexible alternative to RG405 that is flexible, not very thick and has similar characteristics? If not, how would you rate RG316 cable - will it be good enough?

 

[Dan Mills]

That will depend on your link budget surely?

BT is 2.4Ghz, so just look up the attenuation for your particular RG316@2.4GHz (It does vary more then is good between the cheap stuff and the good stuff) and see if your link budget can live with it.

For example one version I found from a respectable manufacturer specified 2.4dB/m @ 2.4GHz, your link budget will decide if you can live with this (Don't forget to allow for connector losses as well).

RG142 gets you less then 0.8dB/m but is a rather thicker cable.

For lower loss you are into foam dielectrics which are not bad to handle but for which the specifications on minimum bend radius **MUST** be respected, such a cable is S04272B from H&S, 0.45dB/m @2.4GHz.

All of these numbers apply to HUBER SUHNER cables other manufacturers may differ.

Regards, Dan.

 

[pkaras]

I was expecting to get that cable assembled for under $100. Not sure if that is enough though.

I am facing two issues:
1. I cannot find RP-SMA right angle male solderable connector from well known company. It seems I can only get it from eBay/China, but quality of those is very questionable.
2. I cannot find cable that is at the same time flexible/thin and also has relatively low loss. For example, I am concerned that RG405 will not last long if I bend it many times. I think so because it has a solid center conductor (same applies to your suggested RG142). As a comparison, RG316's center conductor is stranded.

 

[Dan Mills]

Err, I think you misunderstand the term link budget......

A link budget is a calculation taking into account transmitter power, connector and cable losses, transmit aerial gain, space loss, receve aerial gain, cable and connector loss and finally recever sensitivity, it tells you what the link margin will be and is not hard to work out, do watch the difference between dBd and dBi however, quoting aerial gain with reference to dBi is a common marketing trick. I generally like to see at least a 10dB link margin, but I doubt you will manage that over a KM with BT.

Here **broken link removed** is an online RF stuff specialist who has good datasheets for the more interesting things (And has both a wide selection of cables and RP SMA connectors from someone sane).

In general you will find that low loss microwave cables are less flexable, it comes with the need to maintain an accurate geometry (RG223 might be a good compromise if you only need a few feet (0.8dB/m @2.4G).
Some of the lab cables are also not bad (succoflex for example), but I would suggest that the real answer is to mount the blue tooth module right on the aerial structure, you cannot get lower loss then having nearly no cable or a few inches of hardline or semi rigid.

73 de M0HCN.

 

[D.A.(Tony)Stewart]

Quality of cables generally is ranked 1) Rigid, 2) Semi-rigid, 3) Flex where larger diameter and high quality core can reduce loss.but also much more expensive, so look at larger diameter flex coax.

how would you rate RG316 cable? 50m @ 2.4GHz attenuation = 95dB Very Very Poor.

PE-C600 Low Loss Flexible Coax Cable 0.590" Diameter With Double Shielded PE Jacket $5.60/m
50m @ 2.4GHz attenuation = 7 dB Very Good

Best bet

LMR 400 DB is a flexible low loss direct burial coaxial cable, its loss is comparable to semi-rigid hard-line cables and has one of the lowest losses for flexible type RF cable. $1.14/ft or $3.8/m

50m @ 2.4GHz attenuation = 11 dB Good

 

[pkaras]

Dan Mills, yes, I have misread your question. Thanks for your advises, I will take them into account.

SunnySkyguy, I think you have calculated it wrongly. I was talking about 50 centimeters, not meters, that's in two orders of magnitude less.
I don't understand why do they call PE-C600 flexible? From its photo, I would say it is semi-rigid: https://www.pasternack.com/images/Product/large/PE-C600.jpg

I have not yet found a cable that has stranded center conductor and lower loss per meter compared to RG316.

 

[D.A.(Tony)Stewart]

sorry about misread on 50 cm.
https://www.pasternack.com/images/ProductPDF/PE-1-4SFHC.pdf

This cable is far superior for low loss 1/4" coax and super flex 25mm bend*radius or 12mm one time. 0.3dB/m at 2.5GHz

- super flex vs Flex and semi-rigid vs rigid are all determined by ratio of bend radius to cable diameter.

- where flex. vs rigid is determined by elasticity.

This solid core helix shield is super flex with a bend R/dia=6