How to Better Wire the BNC Connector and GHz issue.

[Mechatrommer]

great! cant wait for that!
ps: wondering... whats the difference it will make if that SMA-SMA cable is tested winded like in the picture, compare to if its run straight... hmmm 

[jahonen]

And here are the results, first one is with RG-174 + SMA PCB connectors, and second is for RG-174 coax + proper coax connectors. FYI, the cable length is about 1 meter.

It seems that PCB connectors connected this way, can be used to about 2 GHz before loss happens, maybe more. I'm not still sure about reflections, the VNA is not currently around so I can't verify that.

And for your question about how the coax is installed, it does not matter if the cable is coiled or straight, as long as the geometry inside the cable is not distorted. This is because there is no field outside the cable.

Regards,
Janne

[Mechatrommer]

thanx alot janne. its worth a thousand words. you basically concluded the original thread topic, empirically. thanx alot and i mean it.

[saturation]

I second mecha's thanks, jahonen.  The series of photos just nails how good the proper cabling can be.

Reading on SMA connectors, wikipedia says they have a rated life of about 500 actuations, do you think this is true and connect-disconnect cycles wears the connectors enough to be practically noticeable? [ not so much mechanically, but enough to affect its GHz response].

[Mechatrommer]

looking around http://www.amphenolconnex.com/SearchResults.asp?ProductID=189 ordering is a bit confusing. and they seem ship to US and Canada only. so i'm not in the list

[saturation]

Yes, mecha, its only good in North America.  Its probably just a distributor relationship.  Search google for Amphenol or a similar well known competitor for connectors, Asia or Malaysia.

http://www.interfacebus.com/connectors_coax.html

When I'm not sure about components, I just buy one or two pieces and test it myself.  When I'm satisfied with the quality then I buy again.  That's why its good to have a lab with a capability to push your working tools to its highest limits.   At work, we buy only through distributor channels and all the parts are premium price, but 99% they work very well.

looking around http://www.amphenolconnex.com/SearchResults.asp?ProductID=189 ordering is a bit confusing. and they seem ship to US and Canada only. so i'm not in the list

[Mechatrommer]

so i got my lego set from chinarf ebay seller. among most important item are crc9 connector for my broadband usb modem, bnc plug, rg174 cable, and 50ohm termination (which is sux... below) and other needed adapters + sma's. early conclusion i think that the chinarf is know shit about rf, or dont know what he's selling, either way he knows shit about what he did to me.

annoying thing... i ordered 2x 50ohm termination. what i got is one 75ohm and one is 0ohm termination (yes zero ohm!), as arrowed in the 1st pic. other stuff seem fine. except i'm start to question the spec reliability since the terminator is not a good news. if you spot anything peculiar in the pictures pls warn me.

second thing is, i thought the bnc plug crimp is with detached centre pin to be crimped to center wire, but what i got is the center pin is sticked to the plug with only with protruding copper (conn.jpg) not sure whether to crimp the cable to it or solder. that was not so obvious in the ebay listing picture, but i guess my mistake for not checking carefully. and rechecking, he inded doesnt sell any such detached center pin for rg174 cable, only for rg58.

last picture is dds signal with diy 50ohm termination with original dds 50ohm cable (ch1) (3.5Vpp from dds signal) and chinarf's 75 ohm (75.74 to be Uni-T's exact) with diy 75ohm cable ch2 (synch out). look jaggy, not sure why, maybe dds instability. any explanation?

ok most important question, pls help:
1) having read how to connect cable and connector together from earlier link, i think the idea is to shield centre wire as much as possible with metal shield (ferrule?). and for stronger connection, can i solder the arrowed in conn.jpg? can i solder the centre wire to the centre pin?
2) any possibility repairing the 0ohm terminator? seem hard to pull out, it is a solid metal.

i hope to hear some advice before i put these legos together.

here again saturation's link for my reference...
http://www.dxing.info/equipment/rg_174_coax_bryant.dx

[Mechatrommer]

so this is how it looks like inside the RG174 cable. the centre wire is many small copper wires twisted together, not one single solid copper like my earlier 75ohm white cable. and its diameter is a bit smaller compared to rigol probe wire (2.77mm vs 3.01mm)

[nyo]

The bnc with 2 screw terminal you got is a balum, it has an internal resistance already.

[Mechatrommer]

The bnc with 2 screw terminal you got is a balum, it has an internal resistance already.

i measured it has no resistance. just a plain BNC to "2 wires" adapter.
here is another pictures the chinarf asked for verification. she seem not to understand the problem. "she" stated she will forward it to "her" store dept.

[joelby]

The 0R terminator might not be a broken 50/75R terminator - sometimes you do actually want a short circuit (e.g. for calibrating a network analyser).

It does seem like they've mixed up their parts though Can you buy them locally and test them in store? Jaycar sell 50R terminators here - they're not too uncommon.

[Mechatrommer]

The 0R terminator might not be a broken 50/75R terminator - sometimes you do actually want a short circuit (e.g. for calibrating a network analyser).

thanx. good to know there is 0R stuff, but still, that is not what i want. i dont want 0, i dont want 75, i want 50 ohms. i dont have vna, so 0 ohm terminator is useless to me

It does seem like they've mixed up their parts though Can you buy them locally and test them in store? Jaycar sell 50R terminators here - they're not too uncommon.

our local store only sell what most people need here, ie 75ohm cable for tv. even the bnc connector they dont have. list all the 50ohm coax cable in wiki, not a single one they have. do they care a single hobbiest like me? i think not

the seller replied back saying to resend the terminator with normal shipping, they cannot afford express like i paid before, so hope it gets here, and another two weeks to wait, sux! they have excel and fast comm/support though and i deal directly to them, not through ebay since they need immediate payment once "buy it now" button is clicked, which is also sux, so i comm direct to them, seems they are honest seller. but as you said, maybe they got mixed up, so i forwarded any good advice here to them, ie separating 50 & 75ohm parts. hope they listen, for their own good.

[Mechatrommer]

completed my 1st BNC-BNC 50ohm coax. let me go back to previous test... hantek cable (top), diy 75ohm (bottom) ...


and compare with the same 10MHz signal, latest test for comparison pictured below.