werdnah
New Member
- Joined
- Mar 11, 2016
- Messages
- 4
- Reaction score
- 8
- Points
- 3
- Age
- 40
- My Satellite Setup
- Multiple c and ku dishes, full RF matrix switch, various commercial receivers and PCI tuner cards. More HD space than I care to admit to
- My Location
- US
I don't think I've ever posted on this forum before, but seeing as this is where the majority of Ka info seems to be, I thought some people here might find this useful.
I recently picked up a surplus 1M (actually 0.98M) Prodelin dish, former HughesNet. I was hoping it was a 1.2M, but the whole thing, including NPRM dish, and Hughes Ku feed was only $30, so hard to go wrong even though it was smaller than I wanted. When I did a little looking into it, I realized this was a "Ka compatible" dish, and even though it came with a Hughes Ku LNB and BUC, the dish itself is Ka rated, and Hughes had a feed swap you could do to transition to Ka. I'd never looked into the Ka band, and over here in North America, there doesn't seem to be any interest in it really in the hobby community, at least none that I've found. In true DX fashion, perfect opportunity to to have a look around!
I picked up a couple Hughes Ka feed sets (circular depolarizer / OMT / TX filter / LNB / "turtle" BUC) from ebay, one with a feedhorn, and one without. The feedhorn isn't the one that's matched to the Prodelin dish, but I figured I'd pick it up anyways and see how it performs. I also maybe have a line on some of the matching Prodelin feeds, so it'll be interesting to see what difference that makes if I do end up getting my hands on some of those.
I setup the dish with a Ku single polarity feed, got out the spectrum analyzer, and pointed it at something. Then I swapped the feed over to the new Ka feed (using a couple pieces of PVC pipe split in half, a 1/2" piece, and a 3/4" piece on top as spacers to mount the tiny Ka feedhorn into the Ku feed clamp), and kept watching the spectrum analyzer. Wasn't long before I found a bunch of uniform signals on a couple of sats in Ka band. Switching the voltage and adding or removing 22kHz tone going to the LNB sadly did not switch the polarity as I expected it would. A little googling and I found some info on uhf-satcom.com that it takes 27MHz to switch polarities on the hughes ka lnb, not the usual voltage or tone, or diseqc. A little more googling, and I found the Ka B/C overlap thread here where Vipersan came up with the resistor divider trick to use 13v/18v to switch polarities.
When I opened my LNB to do that mod, I noticed that there's a completely separate RF path duplicated for V and H right up to the PIN rf switch which chooses which polarity goes to the connector. In my setup, switching 13v/18v would actually be tricky, and having both outputs at the same time would be advantageous (I have OMTs on basically every dish I have, and dedicated V/H LNBs on everything).
Looking closer, I see the 2 outputs of the comparitor from pins 1 and 7, which are active LOW, do 2 things when one or the other polarity is selected:
1) It turns on a MMIC amplifier (marked C4t - actual part number is BGM1013 from NXP) using the PNP transistor marked t2A, and
2) Forward biases a PIN diode switch (marked 6FW - wasn't able to find that exact part, but a 6Fp is a BAP1321-04 also from NXP, 6FW will be fairly similar), selecting that RF chain to make it to the output.
I wondered if both polarities could be output at the same time on 2 connectors by
1) Connect both control signals to ground permanently so both MMIC amplifiers are on all the time (remove the 0-ohm jumpers close to the comparitor and tie both signals to ground), and
2) Remove the second PIN switch, and just take that RF directly to a second connector.
I found an old (from the 1980's) Ku LNB that had a really nice panel mount F connector on it, and removed it. Drilled a new hole in the side of the Hughes LNB (and the 4 smaller holes for the mounting screws). Then I carefully removed the 2 0-ohm jumpers on the control signals, and tied both of them to ground. Then I removed the lower PIN diode RF switch, the reverse polarity protection diode (right above the PIN switch), and the bias diode, which originally turns on the PIN diode when that polarity is selected, and soldered a small jumper between the left contact of the removed PIN switch footprint and my new second F connector.
Swapped the newly modified LNB onto the feedhorn, hooked up 2 cables, and IT WORKS! On the original cable, which supplies DC, I get one polarity, and on the other cable, the other polarity.
Even though these signals are strong, I can't lock any of them. They don't seem to be DVB-S2 or DVB-S2X. We have similar signals on Ku in NA that show the same constellation patterns in crazyscan, but can't lock, so this is no surprise. Time to check out some other satellites now I guess. I don't even know what satellite this is - I'd have to swap a Ku feed/lnb back on to see where it's currently pointing.
Now I wonder if almost any LNB can be easily modified for both polarity output simultaneously. I'm guessing enabling an MMIC amplifier for one RF path or the other, and switching one path to the output connector using PIN switches is probably how basically all LNBs work!
Next I need to make a polar mount for this dish (hopefully can build that next weekend), and work on getting some LNBs for other Ka bands!
Couple pictures of the dish and the feed:
I recently picked up a surplus 1M (actually 0.98M) Prodelin dish, former HughesNet. I was hoping it was a 1.2M, but the whole thing, including NPRM dish, and Hughes Ku feed was only $30, so hard to go wrong even though it was smaller than I wanted. When I did a little looking into it, I realized this was a "Ka compatible" dish, and even though it came with a Hughes Ku LNB and BUC, the dish itself is Ka rated, and Hughes had a feed swap you could do to transition to Ka. I'd never looked into the Ka band, and over here in North America, there doesn't seem to be any interest in it really in the hobby community, at least none that I've found. In true DX fashion, perfect opportunity to to have a look around!
I picked up a couple Hughes Ka feed sets (circular depolarizer / OMT / TX filter / LNB / "turtle" BUC) from ebay, one with a feedhorn, and one without. The feedhorn isn't the one that's matched to the Prodelin dish, but I figured I'd pick it up anyways and see how it performs. I also maybe have a line on some of the matching Prodelin feeds, so it'll be interesting to see what difference that makes if I do end up getting my hands on some of those.
I setup the dish with a Ku single polarity feed, got out the spectrum analyzer, and pointed it at something. Then I swapped the feed over to the new Ka feed (using a couple pieces of PVC pipe split in half, a 1/2" piece, and a 3/4" piece on top as spacers to mount the tiny Ka feedhorn into the Ku feed clamp), and kept watching the spectrum analyzer. Wasn't long before I found a bunch of uniform signals on a couple of sats in Ka band. Switching the voltage and adding or removing 22kHz tone going to the LNB sadly did not switch the polarity as I expected it would. A little googling and I found some info on uhf-satcom.com that it takes 27MHz to switch polarities on the hughes ka lnb, not the usual voltage or tone, or diseqc. A little more googling, and I found the Ka B/C overlap thread here where Vipersan came up with the resistor divider trick to use 13v/18v to switch polarities.
When I opened my LNB to do that mod, I noticed that there's a completely separate RF path duplicated for V and H right up to the PIN rf switch which chooses which polarity goes to the connector. In my setup, switching 13v/18v would actually be tricky, and having both outputs at the same time would be advantageous (I have OMTs on basically every dish I have, and dedicated V/H LNBs on everything).
Looking closer, I see the 2 outputs of the comparitor from pins 1 and 7, which are active LOW, do 2 things when one or the other polarity is selected:
1) It turns on a MMIC amplifier (marked C4t - actual part number is BGM1013 from NXP) using the PNP transistor marked t2A, and
2) Forward biases a PIN diode switch (marked 6FW - wasn't able to find that exact part, but a 6Fp is a BAP1321-04 also from NXP, 6FW will be fairly similar), selecting that RF chain to make it to the output.
I wondered if both polarities could be output at the same time on 2 connectors by
1) Connect both control signals to ground permanently so both MMIC amplifiers are on all the time (remove the 0-ohm jumpers close to the comparitor and tie both signals to ground), and
2) Remove the second PIN switch, and just take that RF directly to a second connector.
I found an old (from the 1980's) Ku LNB that had a really nice panel mount F connector on it, and removed it. Drilled a new hole in the side of the Hughes LNB (and the 4 smaller holes for the mounting screws). Then I carefully removed the 2 0-ohm jumpers on the control signals, and tied both of them to ground. Then I removed the lower PIN diode RF switch, the reverse polarity protection diode (right above the PIN switch), and the bias diode, which originally turns on the PIN diode when that polarity is selected, and soldered a small jumper between the left contact of the removed PIN switch footprint and my new second F connector.
Swapped the newly modified LNB onto the feedhorn, hooked up 2 cables, and IT WORKS! On the original cable, which supplies DC, I get one polarity, and on the other cable, the other polarity.
Even though these signals are strong, I can't lock any of them. They don't seem to be DVB-S2 or DVB-S2X. We have similar signals on Ku in NA that show the same constellation patterns in crazyscan, but can't lock, so this is no surprise. Time to check out some other satellites now I guess. I don't even know what satellite this is - I'd have to swap a Ku feed/lnb back on to see where it's currently pointing.
Now I wonder if almost any LNB can be easily modified for both polarity output simultaneously. I'm guessing enabling an MMIC amplifier for one RF path or the other, and switching one path to the output connector using PIN switches is probably how basically all LNBs work!
Next I need to make a polar mount for this dish (hopefully can build that next weekend), and work on getting some LNBs for other Ka bands!
Couple pictures of the dish and the feed:
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