Antenna help please.

[bravo_echo]

I'm located about 40 miles East of London UK and a new Radar Box user .

I have been trying to install a better antenna for the Radar Box. But whatever I do the little antenna that came with the system gives better, though not good for my location, results.

I have the Watson Radar extender antenna from Waters and Stanton with a radar amp masthead pre amp.
I first mounted it on the chimney stack using RG58 cable, not the best cable but tried it for cost reasons as a fairly short run of 10 mtrs but that gave almost no reception.  Thinking there may be some interaction with other antennas on the stack (about 12-18 inches away) I moved it to a pole in the garden about 25 feet high and above roof height and no other obstructions. Some improvement but not much. Polar diagram showed roughly 15 mile radius at best and about max of 7 or so aircraft displayed. (bear in mind I'm on the Eastern approach to London Heathrow and Stanstead so lots of aircraft about and shown on the network) At times I can actually see more aircraft than show on the radarbox! (via my new antenna)

As RG58 is certainly not the best cable at that frequency I switched today to Ecoflex 10 low loss cable 20mtrs professionally made up and tested. (with N plugs and the pre amp)

I was dismayed to find no difference whatsoever with the low loss cable.  However if I hang the little antenna that comes with the Radar box out of the roof window which is lower than the new and higher gain antenna the polar diagram and number of aircraft rockets in comparison to the new setup. (in the direction not blocked by the house)

My location is not on low ground and there is a good line of site in most directions especially taking into account of the altitude readout from the aircraft.

Can anyone please suggest a reason for the very poor reception?  I am a licenced radio amateur but have never used these frequencies.

 At the moment the polar diagram shows a max distance 17 nm on just a couple of spikes which is unacceptable. (new setup)

Thanks

[Runway 31]

How is it without the pre-amp ?

Alan

[bravo_echo]

Hi Alan

That's one thing I have not tried although I have exchanged the amp in case of a fault but it made no difference.

I take it I should remove it from the system altogether not just switch it off?  Trouble is I would need some sort of cable connector conversion N to whatever is on the Radar box. Do you know the name of those little connectors on the RB?

Thanks

Brian

[Runway 31]

Brian,

Check the polarity on the pre-amp, the search facility though up that as a possible problem.

SMA connectors are what you are looking for

Alan

[bravo_echo]

Thanks Alan

Not quite sure how to check polarity though!

Cheers

[CYYZGUY]

As from personal experience...double and triple check all your connections.  Even a drop of water getting inside a connection can cause a massive loss. 

I first used electrical tape over my connectors, then used liquid electrical tape to make a waterproof seal. My antennas are probably higher then 99% of the people on this board and are exposed to all the rain/sleet and snow that can be thrown at them, and I have never had a problem since..Good range 300 Nm+

[bravo_echo]

Hi Thanks for the reply.

It's certainly not moisture at this stage as everything is brand new cables tested etc.

I have just read that it is possible to get signal loss at that freq if there is a sharp bend in the cable.

Does anyone know if that is correct?

[Lou]

I`m situated just east of the greenwich meridian in east London, my set-up is Watson R/E Kinetics pre-amp and Ecoflex cabling, maximum aerial height is fourteen metres above high tide ( i`m close to the river Thames ) without pre-amp when my Radarbox is working ok is around 150 nautical miles with amp switched in this goes up to about 200 nm for aircraft flying at 38000 ft. I have only taken normal amateur radio precautions with regard to water proofing, I would suggest that you may have a faulty pre-amp or reversed polarity on the power supply to the pre-amp, the RG58 cable should not matter when using the pre-amp as pre-amps are designed to overcome long/dodgy cable runs. By the way during the holiday season I often have more than 300 planes in myflights at peak hours. Regards Lou

[bravo_echo]

Thanks for that Lou

I have never had more than 15 aircraft max. I'm located Nr Southend about 43 mtr above sea level.
I have had two pre amps I doubt both would be faulty. I must admit that when the pre amps are turned on there is not much change in the reception.  This is a real mystery but there must be an answer.

How would I know if the polarity is correct?

Cheers

Brian

[neroon79]

Just a thought, what if the antenna itself is the problem. Maybe for some reason it is "deaf". It's a rare error but anything can happen.

Ingo

[Runway 31]

Does this look like your problem Brian http://www.airnavsystems.com/forum/index.php?topic=6414.0

Alan

[bratters]

i think I would be tempted to take box and supplied aerial for a ride in the car to a nearby hill or clear area. Alternatively maybe to a friend's house where you can do an independent test.

Once you are confident that your box and supplied aerial are working properly, you can start looking for the problem somewhere in your new set up.

[Runway 31]

I thought about that Bratters but as Brian stated in his thread opener "I was dismayed to find no difference whatsoever with the low loss cable.  However if I hang the little antenna that comes with the Radar box out of the roof window which is lower than the new and higher gain antenna the polar diagram and number of aircraft rockets in comparison to the new setup. (in the direction not blocked by the house)".  I thought that suggested the box was OK.  Maybe still worth trying though for confirmation that the it is.

Alan

[bravo_echo]

Hi guys

I did post a reply but it seems to have got lost in the ether.

The pre amp power supply is putting out about 16volts the tee about 15.5 should be 12.
As mentioned this is a replacement pre amp both were new.

One thing I did notice when dropping the antenna, as I lowered it and it was at about a 45 degree angle the signal increased quite a bit though still not good but the max range did increase to about 40 miles to the West (aircraft at FL340) and East and rec aircraft up to about 30 in my flights along with the earth symbol which I have hardly ever seen in the my flights listing before.

I have removed the pre amp from the system now, possibly slightly worse than with it but not by much.

Everything is brand new and all but the Radar box has been replaced in case faulty. The fact that the Radar box works I cant believe it could reduce the receive sensitivity.........could it?

Brian

Don't know what to try next.

[Runway 31]

Try Bratters suggestion to ensure the box is working OK to start with

Alan