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

[jeallen01]

Afternoon.

As some might remember, when I installed the various cables from the dishes at the end of the garden to the house mid 2016, I fitted Smart Priority Switches (SPS) about 1/2 way along the cables, and I also installed line amps (Axing SVS 2-01) on the input side of the switches to try to compensate for both switch and cable losses. I put the amps there because "received wisdom" from various sources indicated that this should be the best place - and not actually at the dish ends of the cables.

However, the experience with another line amp at the far end of the cable to the 1090MHz antenna for the SDR unit indicated that there was quite a lot of signal strength to be gained by doing that (not withstanding that I later had two SMArt SDR unit failures which might/might not have been caused by the DC power injection on the SDR end of the cable - that's still "work in progress" to find out what happened & why. Now got the 2nd replacement unit from NooElec and will run it without the amp/dc injection for the time being!)

Anyway, this morning, I removed the sat line amps from the SPS locations and remounted them immediately on the outputs of the Inverto Black Twin Ultra on the Triax dish, and then rechecked the Signal Strength & Quality and general reception on weaker sats like 31.5W & 7W (using ProgDVB V7.17.3 with the DVBS952 card in the X275 - now in the lounge) as compared with what I was getting a few days ago.

Can't give exact quantitative indications of the improvements, but the indicated Signal Strength required to open weak channels appears to have decreased, there are slight improvements in SQ, and stations that do open tend to do so more quickly and cleanly.

Anyone else have something to contribute on this subject?

 

[PaulR]

All I can say is that in theory the best result is obtained by putting the amp as close to the LNB as possible. This way you are amplifying the wanted signal when it is at its maximum signal to noise ratio. Anywhere else will also amplify the signal, there just won't be as much of it to amplify.

This is disputed by people who have put the amp in the middle of the cable run for reasons I don't exactly understand but I think may be something along the lines of halving the distance therefore halving the noise amplified. Why received wisdom should indicate this second point I don't know but I'm glad that you've found that the way things should work best theoretically is actually the way in practice.

 

[jeallen01]

Paul

I consider that you first para is correct, but I went with the "received wisdom" outlined in the second to begin with - and then my more recent experienced, as outlined, did tend to contradict it, as does what I found this morning. Thus it appears to be correct to put any such amp as near as possible to the LNB (in the same way that you would normally put a head amp as close as possible to a terrestrial DTV etc., antenna).

The only exception of which I can think would be where the received signals are very strong and might overload the amp and/or connected receiver and so cause distortion, harmonics, etc., - but then you would (or should) not need to use an amp in those circumstances anyway.

Nevertheless, I raised the point to find out what others might think or have found.

 

[PaulR]

The only exception of which I can think would be where the received signals are very strong and might overload the amp and/or connected receiver and so cause distortion, harmonics, etc., - but then you would (or should) not need to use an amp in those circumstances anyway.

Exactly.

 

[Channel Hopper]

What is the total length of cable from dish to tuner, and apart from the sps units, are there any other connections along the lines ?

What type of cable is installed ?

 

[jeallen01]

CH
Amps are hanging below the LNB.
Total cable length is probably around 30m (difficult to estimate accurately as it has a tortuous path). 85% of it is WF100, and the last few metres are air-spaced double-screened but can't see/remember exactly what it is.
Other connections - the SPS are in a waterproof box, with coax links to couplers on each side of the box; cables come through the house wall into a pattress box with couplers in the lid.

 

[Channel Hopper]

If it is quality cable, 30 metres should be no problem at all, though tight radiusing, or proximity to mains cable may affect specific frequencies.

I would remove the amplifiers completely and try scanning without them since they might be introducing noise of their own.

 

[Channel Hopper]

What's a pattress box ?

 

[jeallen01]

What's a pattress box ?

!!

 

[Channel Hopper]

Ah, ok. This might be the problem, that or the final flylead used.

Can you try pulling any more cable out from the floor, or through the wall and connecting directly to the receiver ?

 

[jeallen01]

If it is quality cable, 30 metres should be no problem at all, though tight radiusing, or proximity to mains cable may affect specific frequencies.

I would remove the amplifiers completely and try scanning without them since they might be introducing noise of their own.

I understand your point, but, like I said in the first post, an amp under the 1090MHz (which is not so different from Sat IF frequencies) collinear for VRS made a substantial difference to the strength of the signal levels at the NooElec SDR module (check that thread for the splatter diagrams before and after the amp was fitted) - and the SDR cable set-up is exactly the same type/length as the sat ones, except that no SPS was fitted in the line to the SDR unit.

Therefore, I think the amp does make a positive difference.

 

[Terryl]

I would not use any of the so called consumer grade satellite amps, in past tests all I saw on the spectrum analyzer after the amp was noise floor increase. (more junk for the trunk)

Better quality or a coax with a higher frequency response or less signal loss at the high end should be used.

Now a commercial grade amp with band pass and band reject filtering would work better, but they cost a bit.

On long runs up to 300 feet I use RG-11, longer then that I use LDF-500-75 heliax, anything over 500 feet and you can go with a fiber feed, but then your talking a new mortgage on the cottage.

 

[jeallen01]

Ah, ok. This might be the problem, that or the final flylead used.

Can you try pulling any more cable out from the floor, or through the wall and connecting directly to the receiver ?

No chance !
- the upstairs cables in the office are pretty much (give or take a foot) as tight and as short as they can be because there is only one usable place in the room for the sat receivers/SDR PC and so on, and, unfortunately that's on the opposite wall to the wall with the cable entry pattress box .
- the cables downstairs run from the SPS box, under the conservatory and lounge floors (very little slack) and up behind where the X275 is located; if anything they are shorter than those upstairs to the office.

Anyway, I don't think a foot or two either way would make much difference to the signal level over a distance of 30m~100 feet!
As for the final flylead setup (there are a couple, and again there's no alternative), they were exactly the same before and after I moved the amps in the lines to the dual tuner card - and there was noticeable signal/quality improvements afterwards.

 

[Channel Hopper]

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.

 

[PaulR]

My first advice about amplifiers is that it's probably best to do without them. BUT, the question is, if it has to be fitted, where should it go?

 

[jeallen01]

I would not use any of the so called consumer grade satellite amps, in past tests all I saw on the spectrum analyzer after the amp was noise floor increase. (more junk for the trunk)
Better quality or a coax with a higher frequency response or less signal loss at the high end should be used.
Now a commercial grade amp with band pass and band reject filtering would work better, but they cost a bit.
On long runs up to 300 feet I use RG-11, longer then that I use LDF-500-75 heliax, anything over 500 feet and you can go with a fiber feed, but then your talking a new mortgage on the cottage.

All very good ideas, if you have the space, money, cable ducting and so on.

I'm not going "mad" over all this because the sizes of the dishes I can have and the E-W angles of view are limited by where I live, and therefore the "cost benefit analysis", including that of commercial amps, for making a case to spend a lot just doesn't stack up - and the mortgage would have to be on a new property some way from here where I would have more "flexibility" (and getting another mortgage - paid the last one off 19 yrs ago - is the last thing I want or need at my age as I would still be paying it off when I die!).

The point of the thread was to try to get comparative experience and comments, and so far, no-one has come up with anything much that substantial.

PS: have used heliax in my time - something like an inch or more in diameter and an absolute pig to work with where I needed to use it to set up an EMI measurement site on the roof of the HP building where I then worked.

 

[jeallen01]

My first advice about amplifiers is that it's probably best to do without them. BUT, the question is, if it has to be fitted, where should it go?

Exactly

 

[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.

You certainly have a point w.r.t. the matching of the 50 Ohm nooelec device to the 75 ohm WF100, and I was a little concerned about that when I connected it all up but it did seem to work effectively.

That is, until the amp was added and the SRD modules started failing - as I said in the Trouble Shooting thread, there is a possibility that the SDR device RF input gets overloaded when the amp is added (and maybe a series attenuator would help - got a few small ones around somewhere), but that's not going to be a problem with the sat receivers.

 

[Channel Hopper]

Exactly

OK then. 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.

Even then it was recommended that if at all possible a larger diameter cable was used to lower the attenuation per ft, signals were only 950-1750 MHz and almost all clients of mine accepted going up a foot (or three) in dish size to compensate.

Nowadays the LNBs have a much higher output, they are far more stable - allegedly - and tuners can cope with quite a bit more than the 18/27MHz transponder / channel bandwidths of old.

 

[Channel Hopper]

Anyway, I don't think a foot or two either way would make much difference to the signal level over a distance of 30m~100 feet!
As for the final flylead setup (there are a couple, and again there's no alternative), they were exactly the same before and after I moved the amps in the lines to the dual tuner card - and there was noticeable signal/quality improvements afterwards.

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