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70MHz / L-band Combiner

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Aug 7th, 2009 at 6:37pm  
Does anyone know of a combiner capable of passing 50MHz - 1450MHz ?  I want to combine an L-band and 70 MHz signal to be viewed at an analyzer input so I don't have to move cables or buy a switch.  This would be monitor only - not production.  Thanks in advance for the help!
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Eric Johnston
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Reply #1 - Aug 18th, 2009 at 9:16am  
Try three very small 50 ohm resistors in a triangle where the three cables merge.  Bind the three cables very securely side by side and wind copper wire around the braids to bond them together.  Solder the resistors across the ends of the cables, using shortest possible lead lengths.   Wrap the resistors in insulation.   Put foil over the insulation and bond to the braiding.  Wrap insulation overall.

Or, buy Minicircuits ZFRSC-2050, flat from DC to 2000 MHz.  http://datasheet.digchip.com/302/302-00707-0-PRSC-2050.pdf

Either way, very poor isolation (6dB), so check that leakage of 70 MHz into the L band and vice versa will not cause interference in your transmit/receive system.
...

The above is intended for merging two 50 ohm cables into the input of a spectrum analyser. It is not suitable for connecting satellite TV receivers to an LNB, where a DC power path is required.

Best regards, Eric.
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« Last Edit: Sep 23rd, 2011 at 9:49am by Eric Johnston »  
 
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Reply #2 - Sep 23rd, 2011 at 12:03am  
Similar question: I want to split the 950-2150 MHz signal from my DirecTV dish to a 2nd std definition receiver in my garage lab.  I know there's some 22 kHz or DiSEqC signals between the existing std def receiver and the LNB, but maybe I don't need to pass the low freq stuff between the 2nd rx and the LNB?  What do I need to split off part of the signal? I'm assuming that splitting 3 dB or so isn't going to have any effect on the picture & sound, since the LNB sets the fade margin, etc. of the system.  Thanks!
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Reply #3 - Sep 23rd, 2011 at 7:10am  
Quote:
Similar question: I want to split the 950-2150 MHz signal from my DirecTV dish to a 2nd std definition receiver in my garage lab.  I know there's some 22 kHz or DiSEqC signals between the existing std def receiver and the LNB, but maybe I don't need to pass the low freq stuff between the 2nd rx and the LNB?  What do I need to split off part of the signal? I'm assuming that splitting 3 dB or so isn't going to have any effect on the picture & sound, since the LNB sets the fade margin, etc. of the system.  Thanks!

I think this does the job.
...
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Eric Johnston
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Reply #4 - Sep 23rd, 2011 at 9:44am  
The 3 dB splitter shown above has DC power pass on both sides.  This means that either receiver can power the LNB and send 22kHz tone to the LNB.  This is ideal if only one receiver is switched on at any time. The single, powered on, receiver has full control of the LNB.

If you have both receivers switched on, then you need to decide which receiver will control the LNB. Then turn off the DC power and 22kHz tone option on the other receiver.
The frequency band selected (22 kHz tone on/off) and polarisation selected (DC volts +13V or +19V) will be set by the controlling receiver only.

Best regards, Eric.
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Reply #5 - Sep 23rd, 2011 at 6:39pm  
Sounds good!  Thanks!
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Eric Johnston
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Reply #6 - Sep 23rd, 2011 at 7:17pm  
Here is a reputable supplier:
http://sadoun.com/Sat/Order/Switches/Splitters.htm

If one receiver will always be ON and used to provide power (13V or 19V for polarisation) and control the LNB (22 kHz tone for frequency), then a splitter with DC pass on one side only would be appropriate.

Note that the polarisation and frequency band selected by the controlling receiver will control the range of possible programmes viewable on the other passive receiver.

An alternative strategy would be to replace your existing LNB with a two output version, with cables direct the two TV receivers. No external spltter would be needed as the LNB contains all the complexity - obviously it costs more!.  Ask about the options that might suit your requirements, making it quite clear what satellite you are pointed at and what programmes you want.
wxw
Best regards, Eric.
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