Question on cable connectors

[fredg]

OK, a couple of weird questions.

1) What kind of problems would I run into if I connected my LMR400 cable to a BNC chassis mount? I would be soldering it on....

2) Still using the LMR400, say I made one of the homemade ground plane antennas out of a SO-259 chassis mount, could I directly connect (again with solder) the cable to the SO-259 connector?

I guess I am concerned with loss here...

Can any antenna/cable gurus tell me why I would not want to do this?

EDIT:
How about this... Say I had a short RG58 patch cord with a BNC connector on one end and nothing on the other, could I just solder the center wire of this to the center wire of my LMR400 and then solder the braided shields together. AND can the braided shields be bunched and twisted together like you would with 2 pieces of wire? And then lets say you enclosed this mess in one of those metal project boxes from Radio Shack and screwed it to the underside of a desk, LMR400 goes in, RG58 comes out...

I have spliced my cable TV coax this way, twisted the center wires then the braids together, no solder just some tape. Worked fine nice clear picture....

 

[Attackron]

there are different connectors for the different types of cable and bnc rg58 connector is small on the end like the cable is small a round, you need to get the connector for the lmr 400 type cable cost like 3 bucks then you can proceed

 

[GTR8000]

There are answers to your questions in the other thread you started, why not keep everything in one place instead of starting multiple threads for the same exact issue. Maybe you don't like the answers you're getting? Go with connectors, not hack job splices. You're going to introduce MORE loss that way, believe me, to say nothing of all the EMI/RFI you're inviting into the cable assembly.

http://www.radioreference.com/forums/showthread.php?t=94537

 

[n5usr]

2) Still using the LMR400, say I made one of the homemade ground plane antennas out of a SO-259 chassis mount, could I directly connect (again with solder) the cable to the SO-259 connector?

The solder end of the chassis mount is normally where you solder your vertical element. Then four radials off the four mounting holes. You aren't going to have a detectable amount of loss by putting the PL259 on the coax to screw to the other end of the mount.

I guess I am concerned with loss here...

Don't be. At least, not to the point you are (as evidenced by the other thread, too). By the time you get down to the level you're asking about, it's tenths of a dB - if even that much - that you are worrying about.

Can any antenna/cable gurus tell me why I would not want to do this?

Well, I have plenty of disposable income, but I don't like throwing it away on coax. I want to be able to reuse my runs of LMR-400 and other nice coax, and some troubleshooting methods require disconnecting the antenna. It's also a lot easier to move and install both the antenna and the coax if they aren't permanently attached.

And there's just not enough advantage to warrant doing it.

As for the coax splicing, as everyone else said - don't do it. I don't doubt you found the threads you mention on the newsgroup, but I'm almost positive you would find those guys were talking about HF - and quite possibly very low HF (160M or 80M) frequencies. That sort of splicing wouldn't be nearly as big of a problem down there. (I remember seeing those same instructions in the ARRL handbook somewhere as well.)

But by the time you get to VHF and higher (the higher you go, the worse the effect) it doesn't take much of an impedance bump to add loss. Which is why "UHF" connectors are frowned upon - they aren't constant impedance like N, BNC, and other newer connectors. Your splice is definitely not going to be constant-impedance, odds are it'll be an even bigger bump than putting a UHF barrel in. Both pieces of coax being 50 ohm doesn't matter.

 

[zz0468]

You've never really said what frequency your micky-mouse cable splice would be working at. As previously posted it's not a huge deal at HF, below 30 MHz. Frankly, down there it wouldn't make a damned bit of difference. But if you're talking about UHF/800, it's a whole different story.

It has a great deal to do with the wavelength at the frequency of operation. In LMR-400, and at 850 MHz, a 1/4 wave is about 3 inches. How long is your splice? an inch? an inch and a half? 3/4 inch? Those lengths of mismatch in the coax are enough to cause some weird frequency response problems in your coax. How about a 20 db loss in the middle of the 800 MHz band that doesn't show up at all on vhf or uhf? Or maybe it's even worse there. That's the sort of problem you're asking for. If it worked on your tv, it's only because you had enough signal margin to start with that you didn't notice it.

Either get the right connectors, or do whatever the heck you want and stop asking us here. You got your answers. Posting another thread isn't going to make it work better.

 

[fredg]

Either get the right connectors, or do whatever the heck you want and stop asking us here. You got your answers. Posting another thread isn't going to make it work better.

geezz, ya don't have to get angry about it! I posted the other thread as I thought about it more, my thought in this thread was the whole BNC chassis mount thing, then as I thought about it more I came on the splice idea. I started the other thread to better nail down my question as I do not think you can edit the thread title.

Sorry if I runied anybodys day with the two similliar threads and even worse the audacity to even mention cable splicing! Forgive me for having to learn something and not just knowing it already.

Oh and thanks to everyone that answered in this thread and the other, it is pretty clear that I do not want to splice, and yes, I woud bet the info I found on the news groups was in refference to HF. I guess I was unaware of the issues regarding HF being more forgiving.