Oh well, I wanted a new LNB anyway...

[pestie]

Well, today I learned the hard way why we don't torque the bejesus out of our F connectors with wrenches and the like. I had used a wrench to gently tighten a cable onto my LNB. Well, today I wanted to remove that connection and couldn't do it with my fingers, so I got my trusty Leatherman tool and proceeded to twist - the wrong direction. Before I knew it, the nut at the top of the connector, the one that's on the LNB itself, started turning and I knew I'd hosed it. Sure enough, I hooked it back up and got nothing at all. I did, however, take my LNB apart and take a few pictures.

In the first picture you can see that I've managed to tear the solder pad right off the circuit board altogether. I must have twisted the thing 360 degrees before I noticed what I'd done. What looks like a scratch on the stripline traces in the background is actually a circuit board trace sticking out of that big solder blob straight up into the air.

The second picture gives another view of the situation. Look closely and you can see that I've torn some of the stripline circuitry right off. I'm pretty handy with a soldering iron and ordinarily I'd just try to repair this, but that torn stripline makes me think I shouldn't even bother. Everything's so damned critical at these frequencies. It might work or it might not - at least this is damaged at the low-frequency end of the signal path, so I might stand a chance.

The final picture is what I saw when I pulled the cap off the feedhorn. This is a "Besat" 0.3 dB LNB - the cheap ones you can find for next to nothing on eBay. It seemed to work well enough, but I can't help wonder if that huge glob of silicone sealant wasn't absorbing some signal. Maybe silicone is transparent at 12 GHz, but regardless, this is certainly a sign of shoddy manufacturing. Still, I knew what I was getting into when I bought it. I just wanted a cheap LNB to get started in FTA.

So now I'm stuck with an old DirecTV LNB on my dish, picking up a bunch of free radio stations and some ExpressVu barker channels on Nimiq 1/3. My girlfriend's Canadian and is visiting for the holidays so I figured I'd give her some Canadian radio to make her feel at home. Heh... There really isn't jack out there as far as FTA when you're stuck with a circular-polarization LNB.

I guess it's time to order that quad Invacom I've been eyeing...

 

[dirtyshame]

Pestie,
I think I would buy a new one too. Then I would try to fix the old one. If you use wire of about 22 gauge and follow the same path as the circuitry that was pulled loose it should work.

I think I would remove the silicon :>)

Old John

 

[123tim]

I used to work for a company tuning and repairing the other end of satellite communications - the transmission amplifiers. You wouldn't believe some of the things that I saw go out the door. Sealant would be a minor problem. Companies push for more and more output and less quality. It's amazing how good an amplifier can look once the final housing is put on. You never would know what's inside...

Solder spikes (a legitimate tuning technique) at various angles and sizes are actually used to tune the input and output impedance of KU band RF equipment. Judging from the looks of your LNB it looks like no tuning was used at all. Probably a 40 dollar piece just gets wave soldered, cleaned and shipped. Changing the solder might change the VSWR, but probably not by much. You might even make it better than it was in the beginning! Then again, think of what is said about powering up your receiver without the LNB hooked up. I assume that this is a VSWR warning.

Sort of off topic...I once got an amplifier back from the Mid West that had a dead lizard inside. I also worked for a cable amplifier company that had a whole collection of lizards, spiders and other creatures from around the country and world. All from returns. We'd send out amplifiers with loose screws rattling around inside and get back snakes and lizards....

Well, this is pretty boring and off topic...Thanks for taking me back!

Edit - If it were mine, I'd try to fix it too.

Edit 2 - We used circular pieces of metal to tune the waveguides of our amplifiers. We'd use RTV adhesive to hold them on. I'd check the feed horn to make certain that there isn't some type of tuning under all of that goop before I removed it.

 

[Katrinasucks]

123tim...

You only have SWRs on transmission equipment.

 

[123tim]

123tim...
You only have SWRs on transmission equipment.

Katrinasucks,
Thanks,
I'm certainly not an expert by any means, but I believe that an LNB is a transmission device. I never knew anything about LNB's before two months ago, so forgive me if any of this is wrong....A LNB (Low Noise Block converter) converts the microwave transmission to a lower frequency that can be effectively transmitted over cable. I'd like to (respectfully) say then that an LNB is a transmitter. LNBS do have VSWR ratings as well. Check out the ratings on this FTA LNB:
http://www.dvbhardware.com/product_info.php?cPath=17&products_id=58
Input and output return loss was always a critical part of any amplifier (transmitter) that I've worked on. I'm going to go out on a limb and say that it would be the same here. I hope that I don't sound to bold in saying this.
This being said, I know that production and real life are two different things. I agree with Dirtyshame, and would probably try to repair it - just to know for certain.
I only wonder about the warnings that came with my receiver about disconnection the LNB...
You could probably ohm out the output with a meter to see what the internal resistance was. Just worried because I'm talking about someone else's receiver (Pestie's) which I'm sure that he loves.
Take anything that I say with a grain of salt. I really don't know much. I'm certain that a lot of HAMs are involved in this hobby. They certainly could shed a lot more light on this. Please correct me if any of this is wrong. I got involved in this hobby to learn (ok, mostly to have fun ), and appreciate your comments. I don't claim to know what I'm talking about.

Regards,
Tim

Note- I hope that I'm adding to this post, and not dragging it down.

 

[Katrinasucks]

no you're right... I just jotted off the reply before I thought it thru.

 

[123tim]

no you're right... I just jotted off the reply before I thought it thru.

Katrinasucks,

I'm glad that you did It made me think, and do some research to make certain that I was saying the right thing. I learned a good bit from it. Might not be the best thing for me to be commenting on things that I really have no experience with (and have to research after the fact, to verify that what I said was true.)

Feel free to question me at any time. I make a lot of mystakes.

This research has raised a question (Most likely a stupid one) which I am going to post in a new thread Called "LNB's and LNBF's"

Thanks again. I always appreciate your comments.

Regards,
Tim

Good luck with your new LNB Pestie!

 

[Katrinasucks]

About 100 years ago I was a technician at a CB radio shop... Well Ok, not 100 years ago, but long enough that there WERE still CB radio shops.

We (near daily) had customers ask about SWR's on scanners. It became reflexize to tell them that they had nothing to worry about.

Fast forward 100 years and said the same of LNBs not thinking it thru. I answered your PM... Didn't mean anything by the comment, don't take it personal, no need.

 

[pestie]

I'm a ham (N1IHL) and while I'm not an RF engineer, I think it's safe to say that amplifier self-destruction due to VSWR isn't an issue at these power levels. The RF coming out of an LNB is almost microscopic, so its output transistors aren't going to be damaged, even if there was some way to power the LNB without having it connected to something. I suppose it's possible that there's a high VSWR present if you connect a self-powered sat finder to an LNB without connecting a receiver, but even so, the overall signal level is far below the threshold necessary to cause damage.

From the receiver side, the receiver emits no RF, so VSWR isn't an issue. What is an issue, and what I believe is the basis for those warnings about connecting/disconnecting LNB's while the receiver is on, is the 13V/18V DC present on the coax. It's easy to accidentally short the center conductor and outer conductor of your cable while plugging or unplugging it and some receivers don't have overcurrent protection. In that case, such a slip can mean frying the receiver, or at least the circuit that supplies the DC voltage to the LNB. I'm not sure if my Fortec Lifetime Classic is well-protected or not, but I'm certainly very careful not to short the cable if I'm messing with LNB's or sat finders with the receiver on. Yeah, I know, I'm living on the edge, but what fun is a hobby if you don't occasionally get to break something?

For what it's worth, I probably will try repairing that LNB at some point. It shouldn't be all that difficult and it will probably work fine. Even if I get a nice Invacom quad LNB I'm still going to want the wider bandwidth of the universal LNB. I'm in Florida and I can receive some Central/South American beams that use the European frequencies (the South American beam of AMC4, for example). But it's not a priority, just something that's nice to have on occasion.

 

[123tim]

Good to know. I'm not quite living on the edge with my Fortec Classic yet. It's not even a month old and I'm still afriaid of scratching it.