Naughty Mods II: 4x8 Switch with All 18V outputs

[pendragon]

Almost all of my current LNBs are single polarity because I prefer orthomode feeds that allow me to select any polarization from any of the eight receivers connected to my FTA switch matrix. Up until now I have used power inserters on 4x8 powered switches to make sure all of my LNBs get the full 18V they deserve. I found this generated extra wiring and took a lot of unnecessary components, because the powered switches should be capable of feeding 18V out of each port. When I decided to put up a couple of dozen bandstacked LNBs on toroids, I decided enough was enough.

The first step was to find a powered 4x8 switch that could pass 950-2150 MHz for the bandstacked LNBs. Many can't. On a hunch I tested a few WNC SWA-48 switches and they didn't roll off significantly. In fact they seem to pass below 950 MHz just fine, too. The other nice thing about the WNC switches is they have removable top and bottom plates held on with screws. That may reduce their water-tightness, but I was planning to install them inside my attic anyway.

I popped one open and found separate LM317 regulators providing the voltage for each LNB line. That's perfect because LM317s can be adjusted over a wide range. As stock, two of these are set to 18V and two are set to 13V. A quick calculation found I merely had to tie about 560 ohms across pins 2 & 3 of the '13V' regulators to make them output 18V. Here's how:

1. Take the back plate off the WNC switch.

2. Locate the normally '13V' regulators in the attached photo. Solder on 560 ohm resistors (I had some 1% 562 ohm resistors lying around) to pins 2 & 3 as shown.

3. Power the switch up and verify all LNB connections are outputting 18V.

If you want different voltages, the same approach can be used with other resistor values. This mod saves the trouble of wiring up the extra power inserters and having supplies to feed them.

 

[Anole]

oh, yea!

Fred did the same sort of mod to some powered 2x4's a while back.
I'm a proponent of self-powered multiswitches, and also 100% in favor of your voltage mod! - :up
Keep up the good work!

 

[Cadsulfide]

Nice work Pendragon!

Having your lnb's always powered up makes for excellent stability.

 

[pendragon]

Model update:

I've been picking up WNC SWA-48 4x8 switches on eBay because they work well, are easy to modify and often go for just a few bucks. I received a batch today, but the seller substituted what likely is the WNC replacement model: MS4x8WB-WNC. As far as I can tell the only differences are torx screws instead of philips, and F-connector seals instead of caps. The modification works the same and the units still pass 950-2150 MHz.

 

[Anole]

thanks:

As a result of your comments, I tracked down one of these switches.
Found 'em on Amazon for $12.50 , shipped.
Hard to argue with that. - :up
The eBay deal I saw was $10 plus $12-something shipping.

 

[pendragon]

As a result of your comments, I tracked down one of these switches.

Great! These used to be worth a lot more, but as I understand they were spec'ed by D* to work with pre-WB technology (950-1450 MHz). However I discovered some people were using them successfully with WB systems, which meant they were passing at least 950-2150 MHz, and probably down to 250 MHz. Given these units don't support six inputs from an AT9 dish, a lot of places are dumping them. My last purchase was for six of these switches at $30, shipped. No one else bid.

If only I could get my USB box to tune below 950 MHz, my spectrum analyzer says I could use my existing Invacom QPH-031 as a universal Ku LNB.

 

[Smith P.]

Perhaps a DPDT switch could be installed inside of the box, then you could return to 13V any time.

About low freq range - BBC convertor doing swap 250...750 MHz to 2150...1650 MHz . Unfortunately 750...950 MHz range will be lost.

 

[Anole]

oh, yea !

I'm with Smith on the switch mod. Might even do it with a DPST. -
Wonder if you could preserve the water tight feature by using internal reed switches and external magnets.?.
Naw, now we're just getting silly -

Was ordering some Western Digital Caviar Black series 750gb hard drives on Amazon, yesterday.
(apparently the price went up since I placed that order!)
Happened to take a look for this switch, again.
Found -one- used in excellent shape for $3.99... and since my order was already over $25, it came with free shipping.
S C O R E - :up

 

[guapoharry]

...Up until now I have used power inserters on 4x8 powered switches to make sure all of my LNBs get the full 18V they deserve...

They won't work with 13V?

I have some stacked LNBs that came from superdishes. Do they need 18V?

 

[Smith P.]

Yes, bandstacking Dish FSS LNBF usually works with 19-20V DC

 

[Anole]

Gettin' way off topic, here:

I see where you're going. Let me cut you off at the pass -
A 4x8 multiswitch has four inputs, but they are for two LNBs, not four LNBs.

Some time back, JerryT down in Florida, described a big array of bandstacked LNBs on a T-90, and he used the four inputs for four LNBs.
As I recall, he was also using a PCI receiver card, where he had complete control over the switch settings.
In a modern STB, you don't really have the flexibility to do the same, so such a hookup would be unwise.

Likewise, the use of DishNetwork Dish Pro switches (bandstacked) is possible for FTA, but somewhat limiting.
You really shouldn't mix non-bandstacked LNBs, and you are limited to only a few inputs.
I beleive we discussed this all in another thread, 6 or 12 months back.
The DPP-44 (four in, four out) with power inserter, is quite expensive.
The more familiar DP-34 (three in, four out) is common as dirt.
I seem to recall coming up with a way to make a 6x3 or 6x4 array, but that was the end of the line.

But, this thread is for mods to 4x8 multiswitches, and they have considerable value in the FTA world.
Plus, they are a good basic component in a highly expandable switch array! (example: 8 LNBs, 4 receivers )

 

[pendragon]

They won't work with 13V? I have some stacked LNBs that came from superdishes. Do they need 18V?

I employ both bolt-on LNBs for orthomode feeds and bandstacked LNBs from Superdishes. I have no useful performance specs for the bandstacked LNBs, but I've seen sheets for bolt-ons that show lower performance at lower voltages. When I set up my first FTA dish I did some quick tests that confirmed I was getting better SQ with all 18V. As quick as the mods are to make, I simply standardized on this for all of my dishes. No reason for DPDT switches for me.

My only exception is an Invacom quad LNBF that requires different voltages to select polarity. I'll probably change this some time to a quatro version with fixed outputs.

I'm sure Dish bandstacked LNBs will work at 13V, because Dish wants to support very long cable runs (with the attendant voltage drops) and states this in their installer documentation. That doesn't mean they work as well as at 18V, though.

 

[pendragon]

A 4x8 multiswitch has four inputs, but they are for two LNBs, not four LNBs.

Some time back, JerryT down in Florida, described a big array of bandstacked LNBs on a T-90, and he used the four inputs for four LNBs.
As I recall, he was also using a PCI receiver card, where he had complete control over the switch settings.
In a modern STB, you don't really have the flexibility to do the same, so such a hookup would be unwise.

I have to disagree. One of the nicest benefits of the 4x8 switches is dealing with lots of bandstacked LNBs on a T90 or some other multisatellite setup. While most of my use is with computer-controlled receivers like Anole describes, it's just as important that the system work with my STB(s). My Pansat 9200HD has no problem controlling my switch matrix with committed and uncommitted DiSEqC switches plus a bunch of 4x8s. In my current configuration the Pansat is limited to directly selecting one of 44 LNBs, whereas the computer receivers could handle 128 LNBs, but 44 is good enough for me for the time being.

 

[Proximal]

Almost all of my current LNBs are single polarity because I prefer orthomode feeds that allow me to select any polarization from any of the eight receivers connected to my FTA switch matrix. Up until now I have used power inserters on 4x8 powered switches to make sure all of my LNBs get the full 18V they deserve. I found this generated extra wiring and took a lot of unnecessary components, because the powered switches should be capable of feeding 18V out of each port. When I decided to put up a couple of dozen bandstacked LNBs on toroids, I decided enough was enough.

The first step was to find a powered 4x8 switch that could pass 950-2150 MHz for the bandstacked LNBs. Many can't. On a hunch I tested a few WNC SWA-48 switches and they didn't roll off significantly. In fact they seem to pass below 950 MHz just fine, too. The other nice thing about the WNC switches is they have removable top and bottom plates held on with screws. That may reduce their water-tightness, but I was planning to install them inside my attic anyway.

I popped one open and found separate LM317 regulators providing the voltage for each LNB line. That's perfect because LM317s can be adjusted over a wide range. As stock, two of these are set to 18V and two are set to 13V. A quick calculation found I merely had to tie about 560 ohms across pins 2 & 3 of the '13V' regulators to make them output 18V. Here's how:

1. Take the back plate off the WNC switch.

2. Locate the normally '13V' regulators in the attached photo. Solder on 560 ohm resistors (I had some 1% 562 ohm resistors lying around) to pins 2 & 3 as shown.

3. Power the switch up and verify all LNB connections are outputting 18V.

If you want different voltages, the same approach can be used with other resistor values. This mod saves the trouble of wiring up the extra power inserters and having supplies to feed them.

Pendragon which resistor do you use for this mod 1/2watt 1/4, 1w ???

 

[brex2001]

I just did a mod of an SWA48 multiswitch. Used a 1/2 W, 560 ohm, 5% tol from Radio Shack: #271-1116, IIRC $1.29/5 pcs.
Worked out just fine.

 

[Magic Static]

I also used a 1/2watt resistor. It looks like Pendragon used 1/4 watt resistors.

 

[cracklincrotch]

That's all I used, 1/4 watt. Works fine.

 

[Proximal]

thanks guys, I'm no electrical engineer but thought I would take a shot at it and it seems fairly straightforward

 

[danristheman]

I use a zinwell 4x4 switch on DN superdish lnbs you have to use splitter one for even and odd but it does work.

Dan Rose

 

[thedishking]

Thank you for providing this.