C/Ku band retrofit to 12' BUD

[ayelvington]

I'm working on retrofitting a 12' BUD to support digital services (FTA) on C and Ku band.

The receiver and dish controller retrofit have gond very well, but I'm perplexed by the poor performance of the former and replacement C band LNBF (BSC621C).

Both have C-band IF levels significantly below the Ku band. I regret that I have a lot of factors working against me:

The powers that be had me move the receiver 100' further from the dish, so I now have a run over 200' long. I put in two seperate runs (one for Ku and one for C) with independent amplifiers about 100' from the receiver. The DiSEqC switch is 3' from the receiver. I used a switch at the receiver instead of the integrated switch to reduce the voltage drop at the LNBF. I'm using 13/18 H/V switching, so the combined load would brown out the H/V switch.

The dish is an out of support Channel Master in very good condition. It moves very well, and is dead on the Clarke belt from horizon to horizon. I plan to take measurements this week to calculate the focal point to ensure that the LNBF assembly was installed in the right place the first time.

Other than moving the LNBF (phase and minor tweaks were checked with a spectrum analyzer), I am at a loss since I really can't "see" what's going on. I've read earlier post that the BSC621 feeds have performance issues.

Any pointers would be appreciated since this physically is a very difficult installation to work on. I've connected a simplified line drawing to share the vision better.

Two things: I'd really rather not move the receiver. It's in a dedicated A/V space, and the only other option is in the phone closet 100' feet away with the amplifiers... Also, I'm measuring the IF level using the IF Output of the receiver into a spectrum analyzer. There are still analog services we need, but the level is too low for a lock using our commercial analog receiver.

Al

[N9WOS]

I have been running a 7 foot and then a 10foot dish for years with a California amplifier LNB, and then the BSC621 LNB feeding over 200Feet of belden RG6U without any problems on analog or digital. I haven’t had any need for inline amps myself.

The BSC621 seems to have enough gain to drive that length of coax without any problems for my old 4DTV receiver and the new DVB receiver. Pretty much all of the channels that I could get with the receiver at the dish could be watched at the other end of the cable.

Are you checking signal strength at the dish or at the house?

One basic suggestion I have, having dealt with the 200F run between the dish and the receiver. (my setup) Is…. Get a long extension cord, and move the receiver and a small portable TV to the dish. Go point blank. Nothing like ground truth. Figure out what is going on at the dish.

When everything works, put the receiver at the house. If you still have problems, then it’s the cabling.

Run over the basics for good measure!!!!!!!!!!!!!!

If the signals in the 3.7G range are far weaker than the ones in the 4.2Ghz range, then the cabling is soaking up the signal. Try a better quality cable.

LO is above the desired frequency so the IF frequency goes up as the received frequency goes down.

For KU it will be the opposite. If the 12.2Ghz signals are weaker than the 11.7Ghz signals then the cable is soaking it up.

I have had some junky cable that I have run across on directv setups. The low transponders were solid, but the higher ones slowly faded out the higher you went. Above TP22, it couldn’t get a thing. That is with 30Feet of cable between the LNB and the receiver.

All it takes is one bad piece of coax to kill the system, so take known tested good ones and switch out different sections to see if it makes any difference.

Some low quality cables may work fine at short lengths but will fail miserably at long distances. And keep your eyes out for a bad batch of cable. Cable that is from a good manufacture but is damaged or just sucks. It can have horrible attenuation across the band even with no outside signs of damage. Every manufacture turns out a dud once in a while. Impurities in the insulation will make it worthless.

If it is weak across the band, then (excluding bad cable) the LNB mounting may be out of adjustment, or the dish is out of round. Bring along a known good LNB for reference. Test the signal levels at the dish with the reference LNB and the 621. If the signal is still down with the reference then the dish needs adjusted.

With a 12Foot dish, you should have no lack of signal.

[Vitruvius]

Hi Al, I wonder if you had the switch closer to the dish and ran only one main cable that would work... Have you tried it without the amplifiers?

My run is about 150 feet to a 6 ft dish with the switch at the dish pole, and I have two small fixed dishes tied into the switch. I did put an inline amplifier after the switch on the cable to the house, but I really didn't see any improvement.

Yeah, I like solid copper core cable... (Belden makes some good stuff - It doesn't even need to be quad shielded). I have a few strands of steel with copper cladding, and I think it is lowering the signal.

[ayelvington]

I have tried it with and without the amplifiers. The difference was minimal, but I elected to keep the amps in since any margin in my favor was a margin I'm in favor of.

I didn't consider putting the switch in the middle. I'm trying to keep the loads as close to the receiver as possible to reduce the I*R voltage drop that will make thing bad out at the dish.

I am going to bring the receiver out to the dish next weekend (wx permitting) and see how things look right at the source.

The #1 hassle is that I have to rent a VERY large ladder for this job. And I'm tired of having to pick it up and return it a ways out of town. Vitruvius loves DC traffic as much as I do!

Thanks all...

Al

[N9WOS]

I think you are worrying about the IR^2 loss a little too much. RG6U should have a DC resistance less than 15 ohm per 1000 foot.

The internal lnb switch in the 621 only powers one of the two LNB’s at a time. Power draw is only 125ma in C band mode, and 100ma in ku mode.

Since only one lnb is powered at a time, you are gaining no IR^2 loss reductions by running a coax to each lnb. You will still have one 200F piece of coax running one LNB at any one time.

The only problem you would have with voltage drop to the LNB is the 18V of the 13/18 won’t be high enough to switch it into the other polarity. (ie) it will be stuck in the 13V polarity. That will happen if your 18V level drops to 14V to 15V (the switchover point) or lower at the LNB.

The length of coax you would have to have to cause that problem with RG6U coax would be..
Around 2000Feet of coax.

Don’t worry about voltage drop with 200F of coax.

If you are getting enough voltage drop with only 200F of coax, that the LNB isn’t doing the 13/18 switching properly, then you do got coax issues.

[lumpkin666]

200ft shouldn't require an amp as long as you have good cable, good fittings, and no splices. Everytime I've tried an amp, it may increase signal strength, but it introduces just as many problems as it helps - you're amping the crap along with the good stuff, and that tends to make matters worse.

Regardless of the amp, I think you'll find that the BSC621 is your real issue here. Between the fact that it doesn't sit in the feedhorn very well (thus making it hard to get 100% centered), and the well documented fact that it is a low performer as an lnb, you're not going to have terrific success. Sure, you can probably make it work, but when you're fighting 200ft, you don't need a crappy performing lnb dragging you down too.

Albeit, you've gotta deal with what parts you have at the moment. So make sure your dish is tuned well, and that you've got that lnb perfectly centered (maybe use a rod or laser pointer to verify). Test things at the dish, and tune it as good as you can before introducing the 200ft cable.

I'd be on the lookout for a reasonably cheap dual c/ku orthomode feedhorn assembly so that you can do both polarities with some GOOD LNBs!