Just Sharing This In-line Sat amps - and where to put them

[jeallen01]

Can you take a picture or two of the flyleads used and the gubbins on the pattress box cover (or a make/model number)

I'm rather mystified about why you ask, but the front panel of the pattress box is simply for accomdating 4x blank plastic clip-on modules, similar to those used for RJ45 Ethernet sockets.. Those modules have holes drilled in them for standard back-to-back F-connector couplers (with securing nuts), and with the exterior cable runs are terminated by F-connectors to the inner ends of the couplers, and the room cable runs are connected in the same manner to the outer ends of the couplers, i.e. no different to simply joining the two sets of cables with couplers without the front panel in between (but the pattress box makes a tidier and more durable configuration - and covers the hole in the wall!)

Anyway, the tests were done on the X-275 setup downstairs - not the Vu+ Rx in the office.

 

[Channel Hopper]

Every coupler and connector makes a difference, Tesco has a similar tag-line.

I also mentioned radiusing earlier, does the cable come straight into the back box from the outside, or does it turn /twist inside to suit ?

 

[jeallen01]

Every coupler and connector makes a difference, Tesco has a similar tag-line.

I also mentioned radiusing earlier, does the cable come straight into the back box from the outside, or does it turn /twist inside to suit ?

Yes, I'm very aware of coupler-loss issues and I do try to minimise the numbers used, but that's the way it has to be here for a variety of reasons (garden & house layouts, existing hidden cable runs under the conservatory/lounge floors - no real chance of replacing those cables which were put in place before the latest floors were laid -, equipment to be connected and so on), and I do try to maximise the radii of all the bends (NO kinked cables here!).

On the office wall, the bunch of 4 cables come straight out of the wall, through the knockout hole in the back of the box, are then spread out slightly and connected to the couplers - no twists and turns.

 

[PaulR]

Early recommendations (and this was from the early 90's with analogue reception and non sloped amplification) was for about a third down the line from the LNB.

What was the rationale for fitting it there rather right up against the LNB?

 

[Channel Hopper]

What was the rationale for fitting it there rather right up against the LNB?

Many reasons. This is all pre 22kHz polarity switching by the way .

1) Amplifiers were only used in exceptional circumstance since they were noisy in their own right.
2) The LNB was designed to send a reasonable level of signal down a cable to this distance.
3) Below a certain distance one might need an attenuator, beyond this the signal would not be sufficient to drive the minimum requirement of the amplifier.
4) 1750 MHz was a maximum recommendation for cable specification in the industry at the time, but some dualband systems were testing at 2GHz or slightly above (MTI/Uniden).
5) The voltage losses on longer runs would prevent the 13/18V switching on many receiversonce an amplifier was installed at the far end.

 

[PaulR]

The only possible valid reason I can see in the list is no 5. The others don't make any sense or are actually contra to sense.

 

[jeallen01]

The only possible valid reason I can see in the list is no 5. The others don't make any sense or are actually contra to sense.

That seems true, nowadays at least, because modern equipment and cables are far better performers in issues Nos 1 to 4 (and probably 5 for that matter).

 

[Channel Hopper]

That seems true, nowadays at least, because modern equipment and cables are far better performers in issues Nos 1 to 4 (and probably 5 for that matter).

It all depends on where the cable has been sourced from, if it actually performs to the claims made by the seller, and how well the connectors are fitted at any point down the line.

 

[jeallen01]

Your nooelec device I think, is designed for a 50 ohm incoming connection, but -modern- satellite equipment is matched to 75 ohm, though I do have s band and weather satellite stuff in the shed rated at the earlier specification. Whilst you will see a greater gain with the amplifier installed, it is after all going to throw at least 12 dB more at the if band, this may not translate to an improvement at all frequencies owing to standing waves on the line.

You might find a balun or matching swr meter fixes many of the issues,I did give Evan a number of suggestions when he started in sdr but I can't find the specific thread at the moment.

Had a look for coax baluns, SWR meters & ATUs, but couldn't find much/anything that isn't going to cost a lot of cash - also, specifically, I couldn't find (quickly) any SWR meters /ATU's that appeared to be suitable for around 1GHz (most were for much lower frequency CB or Ham bands)

 

[Channel Hopper]

Sorry, can you clarify what is within the post I should be looking at?

 

[jeallen01]

Sorry, can you clarify what is within the post I should be looking at?

Taking your point about matching, I looked for coax baluns, and all I could find was this one which turns out to be a resistive (not inductive) matching device, with the losses inherent in that - anything else with coax connectors would cost a "bomb".
Edited: the only way I could do something similar would be to insert a series resistor into the centre core of the coax between the end of it and the SDR I/p socket - and I can't see an easy way to do that.

Also thought about matching swr meters & ATUs, but nothing affordable appeared to be specced to 1GHz.

 

[Channel Hopper]

I wish I could find the message to Evan. Ill have another look around now Im sitting down.

 

[Channel Hopper]

Ah, it wasn't on the open forum. I had mentioned j-stub / Zeppelin baluns and this link.

A long-wave SWR meter

And a two resistor version that works beyond 2000MHz

Options for matching 75 to 50Ohms on PCB

 

[jeallen01]

CH

Many thanks for the links and I took a good look at them yesterday - concluding that the resistive versions might be feasible if I (possibly doubtful because of the recommendations for surface mount resistors and so on), but anything inductive would probably be not. OTOH was still mulling over the possibilities of simply adding an attenuator (and in fact ordered a cheap 20dB-variable attenuator yesterday as well.

And then I forwarded the following question to Alex at NooElec:

"Still running after 30 hrs


BTW, some of us on that forum to which I linked (but not in that thread) are beginning to wonder if the impedance mismatch issue when connecting the 50 Ohm i/p impedance SDR unit to 75 Ohm cable AND WITH an amp at the far end could be part of the problem – in that the combo might inject higher levels of RF into the SDR input and cause that to fail (the last failure resulted in some aspect of the SDR unit connection still being seen by the PC, but not all of the expected)?


Been looking for a coaxial “balun” to match a 75 Ohm source to a 50 Ohm load as that might help because the performance gain with an amp is substantial – but can’t yet find anything that would work at 1.1GHz, and at a “reasonable” price.


Might have to settle for a simple coax attenuator, but wondering how much attenuation I might need."

His reply this morning was as followings

"It is quite unlikely to be an impedance mismatch issue in an RX scenario. We are still delving into the docs and will provide a response ASAP."

So, now waiting for further info from NooElec on the SDR device issues

MOD NOTE
Post tidied up a little.