Pre Amp = Reduced Range?

[Budgie]

Hi all,

I'm looking for some insight into a problem I seem to have with a Elad A12-1090 preamp that I got second hand off Ebay.
I got new connectors today and got them soldered on to the coax and connected the preamp and T but I'm now getting worse reception with the preamp fitted than I was without it.

The antenna is a Radar-Rama 1090 which on top of a 30-35m pole on the roof.
From that I have a 2m x 6mm coax patch lead with N-type connectors that I soldered myself and tested the end to end connection with a tester.
This goes into the A12-1090 preamp on the mast and is connected to the T by about 20m of Westflex 103.
The T is then connected to the ANRB by a 1m length of Westflex 103 with BNC & SMA connectors on the ends that are correct for that size of cable.

There is 12v from the power supply to the T and 12v coming out of the T towards the preamp, but I've not checked that the 12v is getting to the preamp yet.

Anyway, before fitting the preamp I was getting 170-200 miles range, with a 150 to the south. With the preamp running I'm just reaching 110 miles and there's no noticeable difference whether the 12v supply is plugged in or not.
So, to the questions:
1. Have I just got a duff preamp?
2. Is there any physical way to check that the preamp is working?
3. What would cause such a drop in range even if the preamp isn't working?

I do have the option of making a new patch lead using Westflex as I have enough spare and two new N-type connectors, so would that be worth a try?
I've added a before & after screenshots below, the before is taken over a week and the after is just from lunchtime today but I think you can see the difference.

Thanks for any info.

[tarbat]

3. What would cause such a drop in range even if the preamp isn't working?

A pre-amp without power is likely to reduce range.  So, maybe suspect power is not getting to the pre-amp.  Or maybe the polarity of the power supply is incorrect/reversed (+/-).

[Budgie]

I'll get up on the roof and check that power is getting to the preamp tomorrow but I've just checked the power supply again. It was a centre - supply and when I tested the output from the T it was -12.93 volts.
I've now connected a centre + supply so that the output from the T is +12 volts and will see what happens. 

[tarbat]

I use a similar ELAD pre-amp, and I've just checked, the power supply is centre +.

[Budgie]

Well that seems to have done the trick.
I've just lost one aircraft at 168 miles to the west and another at 189 mile to the NNE so it look like it may well have been the power supply that was causing it.
Now I'll need to find a new power supply for it as the one that's on there just now is from something else.
I wonder how long the previous owner was using the preamp with the wrong supply on it?

Thanks for the help Tarbet. ;)

[Budgie]

Just to confirm that the incorrect polarity on the power supply seems to have been problem here.
I let it run overnight and looking at the polar diagram this morning there, the max range has increased to 220 miles is some quadrants and is, at worst, 150 miles in the direction that I have the Harris Hills blocking to the Southwest.
So it's an overall improvement on what I had before and the preamp only cost £52. :D

[tarbat]

I wonder how long the previous owner was using the preamp with the wrong supply on it?

Maybe that's why he sold it on eBay, because it wasn't working with the power supply reversed!!

A good result for you though ;)

[Budgie]

Could be, he was also selling SAS-1e but for some reason he seems to have had the preamp connected direct the T with a double N-type connector at the box end of the cable run. Maybe it's been like that so long that he didn't notice.
It's not new kit, the front panel on both units are quite warn and you can't see the polarity diagram for the power on the T so maybe he got it second hand but without the power supply.

Still, it's mine now and it works. :)

[eyeinthesky]

Looking good Budgie, thought of getting one myself thanks for the review.

[Budgie]

Well, I thought I would close this one out with the results of running for a week with the Pre-Amp correctly set up and working. I think it's added about 40 miles to the average range on the set up and the max has been extended from around 190 to 260 miles.
The pre-amp is worth fitting but I'm glad I found a second hand one, even if I did have to buy the correct power supply as an extra.

Here's a screenshot of my current polar diagram: 

[tarbat]

Looks like you're getting great coverage now.  It makes me think about subscribing to the network again just to extend my western coverage ;)

[Budgie]

I don't upload to the network, just Flightradar24 as they let me use their interactive map on my website in return. ;-)

[Budgie]

Well, looks like the pre-amp is duff.
It was working fine yesterday but this morning I got up and found now targets on the map.
The blue light on the ANRB was flashing so there was a connection to the PC.
I then unplugged the power to the pre-amp and immediately the white light on the ANRB started flashing away again.
Plugged the supply back in and it stopped.
I even tried the original power supply that I got with the second hand pre-amp and that didn't make any difference, although it didn't stop the signals.
So, as plugging in the power supply stops the signs then I guess the switch in the pre-amp is working but does anyone have any ideas whether it could be the pre-amp or the bias tee that's at fault?

There was lightning around last night but there were no close strikes that my lightning detector picked up.

[CYFC]

make sure your DC power supply, can handle the amplifier load....from what you posted, it could be that the power supply is fading after it heats up...pre-amps draw a large amount of power, maybe in the range of 1 amp or more....GL

[Budgie]

I think the power supply is OK as it's been running 24/7 since September without a fault and I've also tried another PSU with the same results.
When I tried the other PSU I checked the voltage coming out of the bias tee and it's supplying a solid 12 volts so my thinking is that it's the pre-amp that's gone.