Q on an RF attenuation problem

Two things: The Farrell item is 0.140' OD and the micro-coax is 0.250" OD Both of them are intolerant of tight bends, it distorts the internal ID/OD relationship similar to kinking.

pointed to,=20

Cool, let us know how it works out.

I have installed the RG402. Will do some tests over the next few days.

It was very easy to install; easy to form with gentle bends, nowhere near the minimum radius. Dead easy to strip, too. Dead easy to solder to the SMA connectors - far easier than terminating a braided coax. I don't know why it isn't widely used. Cost? The lack of radiation alone would be a huge advantage in many RF power applications.

I found a rather amusing problem though.

Because the outside copper is bare (no insulation) I put a heatshrunk sleeve over it. The heating caused the outside copper to expand more than the inner conductor (obviously) and when I terminated one of the end axial-type SMA connectors, while the outside was still warm, once the lot cooled down, the connector's centre pin retracted inside the PTFE insulator and more or less vanished :) :)

This kind of thing could play havoc with *right angle* SMA connectors, which have no "give" along the cable axis.

So, if doing any heatshrink operations on the outside, do the cable first, leaving the end 2" or so bare, let it cool right down, terminate the ends, and heatshrink the ends separately.

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Can you get SMAs for 0.25" OD coax?

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They were pretty easy to find for 0.250" semi-rigid and i did find a few for coax. UT-S(3)-250 is kind of an in between product. Due to connector availability it may be that 0.140" semi-rigid may be the better choice. Another thing i noticed is that properly torquing the connectors impacts performance significantly. Nor is SMA mating cycle life all that good. An adapter called a "connector saver" on the more frequently mated end may be a good idea, even though it will cost you

pointed to,=20

Interesting. Let us know about the RF performance.

"JosephKK" wrote

to,

Did a flight test today. No difference between the RG402 and RG400. The phone (Hughes 7100) shows just 2 (very occassionally 3) bars of signal strength. Nowhere can I find what these steps mean in terms of db but I have just bought a handful of SMA 3db attenuators on Ebay so will be able to find out that bit at least...

Next step is to replace the second section of RG400 with RG214. This bit is 1.8m long. (The previous bit is 1.5m). The difference between the two cable types is about 0.2db/m.

I find it hard to believe this is going to make any difference, because I would have thought that the phone's signal strength bars must be something like 3-6db per step i.e. way more than any cable loss.

The poor antenna gain must be the biggest factor by far.

I have torqued the SMA connectors with a spanner.

(snip details)

Having watched this thread since it started, I am still having difficulty accepting the basic premise. You have losses adding to a small dB figure and describe the results as marginal. Even removing those lossy elements entirely isn't going to lift the QoS by enough to call it a good/reliable service.

rebel wrote

I agree, but the basic problem is that I don't know what db steps are represented by the phone's signal strength indicator.

If they are 0.5db steps then improving the cable attenuation would help. And there are some really crappy cables around, routinely used for this purpose, which could easily lose 3-5db on the ~ 3.3m run I have.

If the phone's signal indicator steps are say 10db each then I agree with you completely; improving the cabling is like pissing in the ocean.

The other thing is that it is only by replacing a cable totally that one can be sure it isn't a dodgy connector, etc.