Hey guys I have a problem. I noticed it for awhile but just getting around to asking. I have a openbox s9 and a dmx741u lnbf. At night my vertical channels don't come in unless I switch to a ku band sat then go right back to the vertical channel. Switching to horozontal and then vertical it doesn't work again. Now in the morning it is fine again til the sun sets. What could be causing this moisture inside the feedhorn?
Vertical disappears at night
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I've seen Horizontal go out due to cold (here in MN I had one blow out lie that) but never the other way around
I like puzzles. It sounds like your Vertical works fine. It is the switching from Horizontal to Vertical that only works in the day and not at night and the problem only exists while viewing C-band channels. I will also assume that you have already verified that the horizontal signals you receive are indeed horizontal signal listed in Lyngsat such that your LNB is not 90 degree out. As written above, the problem is normally switching from Vertical to Horizontal that causes headaches.
How far is the Dish from your receiver? What is between the lnb and your receiver in terms of inline devices?
Any chance that you have a back-up receiver to test so we can eliminate your Openbox as part of the problem?
It appears that you can connect your coax directly to the C-band portion of the lnb and eliminate the ku part. That might be a good test.
How far is the Dish from your receiver? What is between the lnb and your receiver in terms of inline devices?
Any chance that you have a back-up receiver to test so we can eliminate your Openbox as part of the problem?
It appears that you can connect your coax directly to the C-band portion of the lnb and eliminate the ku part. That might be a good test.
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It is only on the cband side. I tried the ku side and it's switching from h to v normally. So it can't be the cold theory. It has been puzzling me awhile and it's just one coax no splitters are connected. I think I'm gonna try and get me a good lnb in a couple months.
Can you measure the LNBF voltage for both V & H out at the dish?
You'd need to do it with the 741u attached.
I'd say your V voltage is a little higher than the 741u likes to see.
I recall one member running into a similar problem (don't recall if it was V or H), and he came up with a solution.
He put a silicon rectifier in a little box and bypassed it with a high frequency capacitor. 0.001uf?
(literally wire the diode between two coax center pins, and put the cap across the diode)
The cathode (banded end) would be toward the LNBF, I believe.
That would provide a 0.7 volt drop to the LNBF, but the capacitor would still pass the RF.
Oh, and you might also need another parallel capacitor to pass the 22khz, not sure, haven't done it.
Well, search for the thread where it was discussed - might have more info.
Pretty sure it was this year.
You'd need to do it with the 741u attached.
I'd say your V voltage is a little higher than the 741u likes to see.
I recall one member running into a similar problem (don't recall if it was V or H), and he came up with a solution.
He put a silicon rectifier in a little box and bypassed it with a high frequency capacitor. 0.001uf?
(literally wire the diode between two coax center pins, and put the cap across the diode)
The cathode (banded end) would be toward the LNBF, I believe.
That would provide a 0.7 volt drop to the LNBF, but the capacitor would still pass the RF.
Oh, and you might also need another parallel capacitor to pass the 22khz, not sure, haven't done it.
Well, search for the thread where it was discussed - might have more info.
Pretty sure it was this year.
I didn't need a cap at all and didn't notice any Q loss and my diseqc and 22khz switchs worked just fine. [but I put a 100pf in just for comparison. None noted.] It's a cheap simple test. I did this first with my Pansat 9200. All my Ku lnbf's switched polarity, the C band (DMS241) would get stuck on H. V voltage slightly above 14v. diode dropped it to 13 to 14v. Polarity switched good then. The Openbox also requires the diode inline.[?]
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I spent a lot of time trying to get a buggy dmx741 to not get stuck on H polarity on the cband side only (ku worked fine). Bought another dmx741 a year ago and have not had the problem since. It was a bad unit.
no capacitors?
Those 1N4000-series rectifiers are for low frequency, so they have a lot of self-capacitance.
As for the 22khz, that's probably more like a fluctuation in the DC for the purposes of discussion, so I can see that working without a capacitor, too.
If I had a "bad" LNBF, and no spares, I'd certainly use the diode trick.
It's trivial to accomplish, maybe even some heatshrink with the diode inline on a short piece of coax.
If you kept it in the house, right at the rear of the receiver (or switch), it'd never be subject to weather nor flexing.
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I don't have a 741 any more, so I can't look.
Ya think maybe one could lift the C-band side cover and put the rectifier right in there?
Also, I wonder if the problem was limited to early production 741-U models?
I don't off hand recall anyone having trouble with the non-U's.
Those 1N4000-series rectifiers are for low frequency, so they have a lot of self-capacitance.
As for the 22khz, that's probably more like a fluctuation in the DC for the purposes of discussion, so I can see that working without a capacitor, too.
If I had a "bad" LNBF, and no spares, I'd certainly use the diode trick.
It's trivial to accomplish, maybe even some heatshrink with the diode inline on a short piece of coax.
If you kept it in the house, right at the rear of the receiver (or switch), it'd never be subject to weather nor flexing.
edit:
I don't have a 741 any more, so I can't look.
Ya think maybe one could lift the C-band side cover and put the rectifier right in there?
Also, I wonder if the problem was limited to early production 741-U models?
I don't off hand recall anyone having trouble with the non-U's.
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I was going to suggest a new DMX-741S instead of a U as the Ku side of the U LNBFs is kinda funky at best and it's good to have "spares" around for testing purposes. I bought one of those U models by mistake when I got my first one then got the S models after that and never looked back. Have two of the S LNBFs on my systems now and have no problems with either that I know of. Now I only use the U one when I need a test piece.
I did think of this, and did remove the cover to look. Would require diligence in neatness to accomplish as there's little room between the F connector and board. I've covered my LNBF with a cut off plastic gallon jug because I'm not sure of the integrity of my cover re-seal job.
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