Attn: Jeff Lieberman - Network Analyzer Info

DanS hath wroth:

Neato. Much thanks.

I did some image processing and resizing for easier viewing. |

I think it's spelled "kludge".

My guess(tm) is that the frequency response is more a problem with the BNC connectors used. They just don't make a good fit. The N and TNC are much better. Also, dissimilar metals (cadmium, silver, gold, nickel) plating might cause a slight increase in loss.

Using your results at 2.4GHz, that's: 2.1dB / 23 connector junctions = 0.09dB per connector pair.

Looking at the photo, my guess is about 18" of connectors. LMR-240 is good for 12.9dB/100ft. 18" would have a loss of 0.194dB. Even RG-174 would be only about 0.9dB loss. So much for my statement that it's the same loss as an equivalent piece of coax cable. The connector string are worse.

Thanks again.

On Wed, 12 Jul 2006 09:01:32 -0700, Jeff Liebermann wrote in :

Wouldn't (sm) would be more appropriate? ;)

John Navas hath wroth:

It's actually an inside joke. One of my former clients was looking for a suitable acronym for their for-pay support organization. I suggested GUESS (Global User Extended Services and Support). Although management failed to appreciate my suggestion, the acronym stuck and was commonly used until almost all support was outsourced to India. Since then, I've used the term to describe my highly intuitive and seat of the pants method of answering technical questions.

However, I think you're right. It really is a service mark, not a trademark. The problem is that most users wouldn't understand the (sm) tag. Methinks I'll continue to mislabel it as (tm) to avoid having to answer "what's the (sm) mean?".

Jeff Liebermann wrote in news: snipped-for-privacy@4ax.com:

I don't know if the BNC _design_ has anything to do with it. They are the same as TNC, except quick-release and not threaded. The chain had 2 BNC MALE barrels in it that are quite old silver plated ones.

I was actually a little suprised about the 2.4 gHz performance. I didn't think that there would be that much loss. (Although still far from the .25 dB I was taught.)

I'll try to see if I can dig up a bunch of 'N' only barrels and re-check it then with out the connector type change.

If I am able to, I'll be sure the pix are a little better. Those were just quicky, non-tripod shots. It would be a good idea to to the picture resolution back up and shoot from further back to minimize the CRT's apparent curvature, although I've gotten much better shots with the only difference being a tripod.

The final outcome though is really that connector connections do not introduce nearly as much loss as expected, and having an adapter or 2 in- line will most likely make no detectable difference. If it does, there has to be something electrically wrong with it, like an errant braiding hair or a bad crimp.

As a side-question, have you ever used Radio Mobile (a freeware prop study tool) ?

Regards,

DanS

Wouldn't the fair test be a single piece of coax at least many wavelengths long, with a single connector pair introduced into the middle of it? I'd think that the reason you can have all those connectors stuck together with so little loss is that they interfere with each other because they are so close. For instance, a capacitive section near an inductive section (if close enough together) might look less lossy than either of them individually.

True. However, the connector alignment is much better with a TNC than with a BNC. The BNC tends to wiggle quite a bit. If the center pin or shield fingers get misaligned, the loss and leakage goes up somewhat.

Agreed. 2.1dB is a little higher than I would have expected for 18" of connectors at 2.4Ghz. Possibly, one of the adapters has a bad dielectric. Any phenolic insulators mixed in there (I doubt it but I sometimes get a surprise). I have a few N connectors with mica filled phenolic I save to show the non-believers.

Sounds reasonable.

Yep. The number of the week is 0.1dB per connector pair.

Oh yes. I've been abusing it for years.

carry the California west coast SRTM data around with me on a DVD. Here's one I did of the local ham radio repeater: can post more if you're interested (after I clear out some diskspace so I don't go over my quota). I have a bunch I did at 2.4Ghz for various WISP's, but I can't post those. Suffice to say that theory and reality were fairly close agreement. I also like to do the stereoscopic views with the red and blue glasses. I've also been tinkering with using Google Earth for the map.

Hint: Use SRTM maps, not DTED or DEM.

The problem with Radio-Mobile is that the learning curve is a bit long and the order and sequence of operations is far from intuitive. Of course, like all good programs, the documentation sucks. See:

tutorials and support.

Jeff Liebermann wrote in news: snipped-for-privacy@4ax.com:

You are right ! A lot of the terminology is 'odd'. No offense intended, but I think it is because it was written by a ham guy !!

William P.N. Smith wrote in news: snipped-for-privacy@4ax.com:

I can do that, I'd like to see the results myself.

The supply of smaller length cables is limited though. We have little on- hand, only 8" RG58 w/BNC's, pre-assembled crimps. Other than that, I don't think I want to try the super-cheesy mini-RCA cables made of RG188 (?).

It will be next week. I did two half-days and am off tomorrow. (Sometimes life is nice....rarely....but sometimes.)

Regards,

DanS

You don't want little short lengths, you want long lengths to swamp out the impedance discontinuities. Take a 10-foot cable, measure it, cut it in half, and put a male and female BNC on either half...

Take your time, and remember how much you are getting paid for this.

8*)