Terminators for switches

[lme]

From Arlog:
"Somewhere I did remember somebody mentioning something about terminating unused ports. I happen to have a bunch of them.
When adding them to the unused ports, switching is almost immediate. Before it would be like 7-10 seconds before signal popped up on the screen and a picture showed."
I did install terminators on my Chieta svitch, and the switching is faster, but the switch got so hot that almost burn my hand. And 1 of the terminators got melted !!!!


Any opinions ?

 

[el bandido]

Some of this stuff is like putting a band aid on a bullet wound.

When you have power running through one of those terminators, it will appear to be a dead short as shown in your picture. I have also had that happen by following the suggestion to terminate open ports on switches.

Most of the time, my switch ports and unused lnb ports are left open which in itself is not a good idea. I think it is best to have a cap and nothing more than that installed on unused ports.

Slow switching time, when the time it takes to make the switch is counted in seconds usually points to a bigger problem than the switch. Slow switch times are usually cause by poor coax or connectors. A piece of coax is ran from the house to the switch and people think the coax can last indefinitely. In reality, coax is made from materials that change slightly when it is hot or cold. Coax breaks down over time. If you have slow switch times, the coax and all of the associated connectors should be checked first.

 

[ArloG]

Just a statement. Now that everything is hooked up and working. Damned well if I may say so. Maybe removing the terminators and comparing before/now switching speed to satisfy the masses would be a cool thing.
Have you slapped an ohm meter on an lnb? Band aids are okay to get things working or getting you out of a pinch. Did that for years. But unlike my counterparts practices. I always went back through triage and made things correct and pretty. Because where I worked at I was "It". With 30+ people in my location depending on me so they could get home for a hot meal and Married with Children reruns. with me staying late fixing things properly sometimes way past quitting time. One time I even came to work with the usual "Can you take a look at my machine?"
A cute little Colombian hottie was there first and looked at another girl about to open her mouth. She looked at her and said "Take the number, bitch". We all got along together. Mostly, usually.

So if I came here and mentioned an anomaly with slow switching speed of a switch that I never used before. But had used a diseqc 1.1 8X1 that switched immediately. Not knowing the new one was a 1.0 switch. I punched in some numbers and got a suggestion (and a question) from a cool guy in Florida. "Are the unused ports terminated?" Me: "Ummm, do they need to be?" Him: "Try it".
And why did one switch come with terminators already on it? 'Splain me that, Roosey.
Okay, fine. It worked. NO, IT'S NOT A DEAD SHORT, ya' yaznooks!
CMOS states that all unused terminals need either a pullup or pulldown resistor. No floating pins. Or you get erratic operation.
Well low and behold. One of the schematics with actual controller IC part numbers. Looking up the datasheet. CMOS Technology. Ding!!!
The Geosatpro 8X1 on my bench under the microscope (trying to get better educated on PIN diodes). The controller is the typical etched variety. No part number to be found.

So. Imma' gonna' undo them there terminators and see what happens. My coax is impeccable. My crimps are fantastic. Who cares about shield foldover over the jacket so you don't end up cramming it down inside inside when you insert the connector? Okay I confess. I don't have a torque wrench for coax fittings. But I surely can bolt down the heads on a 440 or 426 like a boss. 440, 17 bolts/side in 3 steps. Yeah. Haha.


Simmer down there Seth. Take a breath.
Is 107W still alive with an active transponder? Because 105W is blaring so much that my Mio's signal meter is floored for many tp's that used to have 13-14 dB. And I'm "shooting" thru treetops that you'd never get a decent signal before. And my "too much" stuff is in a nice NEMA box. Maybe not bonded to NEC specs. But should be adequate.
And after almost a year of being parked on one satellite. I'm back in the saddle again. Blew in my satellite locations wireless using Virtual Here server on my router and FTDI cable from it to the dish mover. And the client on my lappy to make a virtual serial port. That's my band aid, fellers.
Appreciate all of the tips, comments, criticism. Ah'll be bock.

 

[el bandido]

Grab a-hold of one of those terminators with bare fingers after it has had voltage applied to it for some time. then tell me it is not a dead short while the burn blisters are forming on the ends of your fingers. You won't do it but once and will well remember it. Perhaps not the exact definition of a dead short per-se, but it won't matter as the finger blisters form.

Use the least amount of parts in an antenna installation. You won't go on a mountaintop where the professional transmitters are and see parts installed that are not needed unless the tech was incompetent. Adding extra parts diminishes both performance and reliability.

Bends in coax cables change the impedance of the cable and diminish performance. Bends in coax cables causes premature cable failure. What you have should run a long time, but it would probably run longer and be more efficient with less parts doing the same job. For sure, you would have less coax bends if less parts were used.

A 12 foot satellite dish for C band is roughly the equivalent of a 1.2 meter dish for ku band. The proper size for a C band dish that will eliminate most signals from a satellite 2 degrees away is 4.5 meters for C band. TNAP 5.1 images generate scan reports that show signal strength for each transponder as it is scanned. These reports help in understanding what is happening on a dish system and WHY. An example is shown here:


Bends in coax should be avoided when possible. 90 or 45 Degree connectors are usually a better choice.
What happens to coax when bent video:

 

[ArloG]

Assumptions. Remember the guy who suggested if a certain person were to obtain a said enclosure, to get a good one?
Well to size up one. He took a slab of plywood and laid everything on the carpet right in front of the satellite receiver. Then, because he has a good buddy who works for the local CATV/ISP provider.
Fashioned up a mess of jumpers with no kinks, sharp bends. With a short chunk of coax to the receiver. Short meaning, oh, a foot and a half, two feet. Rated to three of them-there giga-hurts.

And then after figuring out an unlabeled switch of sorts without the diseqc logo. Turns out to be of the 1.0 protocol variety.

"Why in the heck is it not switching?". Me thinks. Grab a multimeter. Shove a probe. Okay...gently insert the correct size positive probe pin. Into the F connector port. Ground the negative probe.
Start twiddling tuner settings until figuring out that the switch ports are labeled 1,2,etc. But the receiver setting (for diseqc 1.0) port assignments are A,B,C.....
You know the delay sometimes when you're trying to figure out things? Well crap. That didn't work. I'll try this.

Consistently, after trying out the options and "Hell, it's a durned dy-sek one-dot-oh switch". And port A in the receiver tuner setting is port one on the switch, port B is port 2.
Screwing one lnb coax fitting on the switch port 1 in to one Norsat. Port 2 to the other one. Through the power inserter. Because power inserters are cool.
Delay. Like seconds of delay. "0 dB? What the hell....it was just working". And then ba-da-bing. Signal on signal finder.
Do it again and again. De-lay.
I rest my case.

One step ahead of you. Initially both switches were relatively cool to the touch. Added the polymorphic hemimetal devices. Knowing damned well that 75 Ohms is going to pull X mA at X volts.
I done did the calculations because, well I'm lazy and used an online Ohms Law calculator.
Before dark. Walked out to the dish. Felt the switches. Felt the terminators. Cool as a cucumber. Ah swear fo' God. Can I git a witniss!
Switching faster than fast now.

One schematic indicated an NXP MCU. Multipurpose. Programmed to be a switch and peripheral components added to make it one.
"I/O ports are protected against short circuit and transient voltages". "Current limited at......". In a supplemental designers document.
Next witness, your honor.

Your diagram above. It shows a sharp kink. And yeah. Engineer's are always the first ones to inform you that they are. So are those guy's famous for diamond cutting in NYC. Know wam-sayin' bro? Oy!
I believe it's 5 inch radius for RG coax used in these installations. If I have 14.3 dB and I push it and close the radius to 3 inches and signal remains the same. Without kinking. Cool.
That's how impedance of coaxial cable is designed. Distance from O.D. of the center conductor to the outer shield. With insulation and conductor characteristics factored in. And the foil covering on the polyetheylene/Teflon center maintains it if the braided shield should creep. Learned that eons ago when I strung CATV hardline for some bucks out of high school. Don't kink it!. "Why does that dude have a pulley sheave roped to his toolbag?". Long, long time ago.
Screw it. Lets go get a frikkin' beer. I'll even buy. And have a pissin' contest off the bridge when we finally stagger home. You post bail though. Deal?
I might even hang a mirror ball and toss in a few beer tab curtains and a Farrah Fawcett mini-poster inside the box. That'll really gitcha' going! Oh, better yet...Taylor Swift.

 

[Terryl]

You need to know that a 75 ohm coax is not a 75 ohm DC resistance, but a 75 ohm impedance, if you where to short one end of lets say a 1000 foot piece of RG-6 75 ohm coax and use an ohm meter you would get around 10 ohms or less.(depending on the coax manufacture)

Most of the 75 ohm terminators you see out there are just a 75 ohm resistor in a 75 ohm connector shell, and most are only rated at 1/4 watt, if you take the highest DC voltage on a satellite system (18 volts) and put that into a 75 ohm DC load you will get a 4.32 watt load on this resistor, this will definitely burn up a coax terminator rated at a 1/4 watt.

If you need to use a terminator for some reason in your system then make sure there is no DC voltage output on the item than you need to terminate.

You could just use them as a dust cap, just break off the center pin.

 

[el bandido]

Solid Copper 75 Ohm RG 179 is found in a lot of commercial transmitters, receivers, and antenna installs. It is great for enclosed places and heck of a lots easier than working with RG 6 in tight places such as enclosures. A variety of pre-made lengths with connectors are available.

(The Good Ones have gold plated connectors.)

 

[ArloG]

For EB. Thanks for the tip. Already have a plethora of different cable types. Since, yeah, it's a little tight and there's a bag of F crimps waiting. Perhaps a few new jumpers will be in order very soon. Maybe later. It was mocked on a 10 X 10" chunk of plywood. The box was an afterthought. So the jupmpers were reused. The box has more room than expected.

The ever-present Terryl. Faithful lurker from way back! No "need to know". Already do. Like you in the list of forums we frequent, and in person. I get things like "why are my speakers rated at 8 ohms, but they measure 6.3 with my multimeter?". Impedance, dude. AC current in a conductor with the polarity flying back and forth can't flow out both ends immediately. It is impeded by various factors. Yaaaaaa. We know this. My test equipment can measure it. And impedance bridge waiting for when it's needed.
The RR guys. The scanner guys. Over and over touting that they use 75 ohm coax. And others fortifying it.
It it right? Nah. Does it work? Yeah. Makes me cringe inside. Working and correct are different things. Just buy the right cable for chrissakes. And yes. There ARE 50 ohm F connectors.
No need for a tutorial or refresher. I fix "stuff". All kinds of stuff. These days usually under a microscope with hot air station and hot tweezers and a bath of Amtech flux.
A folded dipole antenna is a short. But it's not a short. Why doesn't the final of an RF amp simply fry when a folded dipole is used? It's a short, right? ( already know why....IF the impedance is matched, swr is matched).
Not like the CB dude next to me with a truck stop linear who hashed my TV and stereo every single night. I asked nicely. I asked not so nice. I got replies in my face that I needed to get filters. CB. 5 watts. Of clean power. Not X watts of junk many times over the limit with a POS linear.
Know what? I enjoyed a late night walk at times. One of those nights found me rummaging thru my girlfriend's sewing kit. And in my hands a stout sewing needle found its way.
A little shortcut and it meandered itself smack dab through the center of that truckstop linear coax. I guess sewing needles are tempered steel. Because it went *SNAP* flush with the coax jacket.
I heard the next morning coffee and jibber jabber was accompanied with smoke and stench. Go figure.

It'll settle me, it'll settle you. In the search of a decent 4X1 diseqc 1.1 switch to do away with what wasn't needed with the geosatpro 8X1.