Will A Pre-amp Improove My Range Alot?

[Johnn]

Hi There,
I have just seen other users screenshots with there before & after shots which looks impressive. Do any other users out there find a pre-amp is a big advantage?.
Thanks

Johnn-

[MikeC]

Personally, it added approx 15% more contacts.  A masthead preamp, AS-1090 with a GP-1090 external antenna and BT-12 Bias-T.

Not everyone finds the same results.

[CoastGuardJon]

Hi John, my personal view is that they're useful for overcoming the losses incurred by using long lengths co-ax downlead, but they do need to be as close to antenna as possible (ie mast-head preferred), for RB and SBS-1 (IMO) you need one designed and built for 1090MHz, not a JIM M-75 for example, which is better suited to wide band range use - eg scanner .   For my money, it would come down to the Elad or Kuhne (IMO the RR version!).    All a pre-amp does, is amplify the wanted signal (and also the unwanted noise).   A pre-amp will also input its own noise and losses.

If you've already got a really good signal, a pre-amp could overload or swamp the front-end of the RB/SBS and lose info..    Pre-amps only amplify what is already being received!

I nealy put a comment on Dean's post with his Polar Diagrams, if he's happy with the apparent increase of aircraft being received (although a 100% increase is very unlikely  IMO) then that's great, but the PDs need to be built up over days or weeks, not just a snapshot of a couple of hours, or a single day even, routing is affected by weather and other changing conditions, times of day and days of the week,and most of all the heights of the aircraft that were received.    On GlynH's AN supplied standard antenna, which I've weather-proofed and improved electrical connections, I am regularly seeing aircraft at 250nm if they're above FL330.     I hasten to add, I'm not criticising Dean's post in any way, but Im extremely sceptical about a 100% increase - it could be poor contact in a plug and socket has improved by disturbing the connection.    I think pre-amps are seen as a cure-all, but are more reliant on the placebo effect unless they're bsing used to counteract losses in the co-ax.

Placing a pre-amp at the RB/SBS end of the feeder is a total waste of time and money.

[Dean]

I guess the way to think about a pre amp is as follows.

Plane transmits signal - signal passes through the air - signal arrives at antenna - signal induces a voltage into the downlead - what signal gets to the other end at the Radarbox will hopefully be decoded and seen as a live flight.

Unless the weather is extremely poor then the main losses will occur between the antenna and Radarbox.

If you imagine a range of signals arriving at the antenna across a dynamic range of strength 1 to 100 then we consider what strength we need to get to the radarbox.

Co-ax will have an inherent loss and therefore is probably the biggest factor in the whole equation at the frequencies we are looking at. For instance 20 metres of RG58C will have a loss of 16db whereas RG213 will lose just short of 6db. (each 3 db is a halving of the signal). So if the Radarbox needs an arbitary value of 10 at its input the signal arriving at the antenna down 20 m of co-ax may well fall below that level and hence not get decoded. A mast head pre-amp will hopefully effectively overcome the cable losses.

My plot is ok and is based upon the actual performnce gain of the pre - amp. I've spent 30 happy years as a radio ham experimenting with antennas to recognise when I've actually not wasted my money.

In my view do the following in this order to try and eek out every last microvolt of signal.

Properly resonant antenna for 1090 Mhz installed in the clear outside.
Put it as high as possible but balance this against introducing cable losses if it's too far away from the Radarbox.
Use a quality co-ax with the least possible loss for 1090 Mhz.
Ensure you have made the connections properly.
No tight radiuses on the co-ax down lead.
Fit a decent pre-amp.

Once youv'e exhausted that list then it's a trip to the estate agents for a new QTH.

[CoastGuardJon]

Hi Dean, I agree 100%!!!    As long as you're happy with the results, that's all that matters - whether it's worth spending the thick end of £200 for a minor improvement, is totally up to the individual and their pocket, if there's no signal there to amplify.............     I'm very fortunate living on top of 200' cliffs with the next stop west being the US with the Atlantic underneath, but until I can get an antenna up externally and clear of our gable roof, my "view" east will be very poor.

PS.
I certainly wasn't intending to imply that you've wasted your money, but John asked the question and I'd hate him or anyone else spending out a lot of money on a pre-amp expecting a 100% increase in flights, and be very disappointed with the end result which could even be a decrease in reception.    As a 30yr ham, I'm sure you'd agree with me when I say that any additional connectors or circuitry introduced into a downlead, brings with it some loss and "noise", and whilst a pre-amp may amplify a signal to above a thresh-hold level unless it's got some very expensive filtering, it will also amplify unwanted noise and possibly spurious signals.

[Johnn]

Many Thanks Coastguardjon, Dean & Mike C for your replys, I think I will just stick with what I got at the mo then, as I am happy with the range I am getting and would not want to decrease it.
Thanks Again
John

[Mike_Tassy]

I personally would put any cash I was going to outlay on a preamp, and they arent cheap, I would buy the absolute best coax I could afford.  LDF50 / Heliax with quality N-connectors.  And no adaptors or joiners in between - each adaptor will lose around 1/2 to 1 db.  I have 10 mtrs of heliax connected to a 3 element home made Collinear and I can receive to the max limit 260 nm +
If you need  longer coax you need to use a higher gain antenna to make up for the loss
Mike

[Fenris]

Over the years I've measured hundreds of RF connector adapters. As long as you buy good quality (Greenpar, Huber & Suhner) then the loss at 1.1GHz will be tiny. Most of those I measure come in below 0.05dB insertion loss.

[radarspotter10]

Hi Dean, I agree 100%!!!    As long as you're happy with the results, that's all that matters - whether it's worth spending the thick end of £200 for a minor improvement, is totally up to the individual and their pocket, if there's no signal there to amplify.............     I'm very fortunate living on top of 200' cliffs with the next stop west being the US with the Atlantic underneath, but until I can get an antenna up externally and clear of our gable roof, my "view" east will be very poor.

PS.
I certainly wasn't intending to imply that you've wasted your money, but John asked the question and I'd hate him or anyone else spending out a lot of money on a pre-amp expecting a 100% increase in flights, and be very disappointed with the end result which could even be a decrease in reception.    As a 30yr ham, I'm sure you'd agree with me when I say that any additional connectors or circuitry introduced into a downlead, brings with it some loss and "noise", and whilst a pre-amp may amplify a signal to above a thresh-hold level unless it's got some very expensive filtering, it will also amplify unwanted noise and possibly spurious signals.

hi Coastguardjon
I agree with you,  i have had pre amps since 1960s on ham radio,   cb.  scanners,  and lots of times a wast of money,  i live in a built up area so not so good,  i sold many a  pre amps to say someone out in the country works perfect for them, so i think its down to your location/interference
from pat in happy land