Hi

I would like to improve my airband reception for my local airfield
(Sywell). Currently I can hardly make out what the tower is saying and
struggle with 75% of aircraft as the voice signal levels dissappear
into the noise levels. Most signals do activate the squelch ok, but
the audio noise levels are just to high.

My current setup consist of a dual band (2m & 70cm) vertical fiber
glass antenna (I can't find the exact details at the mo) on a 2.5m
meter pole which takes the top of the aerial just above level with the
neighbouring houses roofs. It then feeds into the loft with about 3 M
of Y[1] cable, through a small lightening discharge unit (which I still
need to put the ground connection in for) and then through 3m meters
more of Y[1] cable. Then inside the loft room it goes into a panel
mount BNC connector and through 1M of RG-59/U cable before going into
the AOR AR900 scanner.

[1] It has no numbers written on it, but it is a 1cm diameter coax
cable
original bought for amateur radio use.

I suspect the loft room is fairly RF noisy as it is my study including
two computers, monitors, ADSL, wireless 802.11b etc. Connecting the
scanner to mains (via it's transformer, or battery makes no difference.

I'm looking for a rough idea of how much the following options would
improve my reception experience against the cost / difficulty of
completing those changes:

1) Change aerial (must also be able to Rx & Tx on 2m and 70cm)
2) Raise aerial by 1m or so, so that it is above neighbours roofs.
3) Change aerial feed cable
4) Ground the lightening arrestor (something I know I need to do
anyway)
5) Change Rx end BNC to BNC cable (is that the right kind of cable?
Impedance mismatch?)
6) Change panel mount BNC connector (does this let noise in due to
short unshielded bit of inner cable or impedance mismatch?)
7) Add a band pass filter for airband at the Rx end
8) Add a pre-amp for airband as close to the aerial as possible

Any other suggestions?

Thanks in advance
Kev

wrote in message
oups.com...
Hi

I would like to improve my airband reception for my local airfield
(Sywell). Currently I can hardly make out what the tower is saying and
struggle with 75% of aircraft as the voice signal levels dissappear
into the noise levels. Most signals do activate the squelch ok, but
the audio noise levels are just to high.

My current setup consist of a dual band (2m & 70cm) vertical fiber
glass antenna (I can't find the exact details at the mo) on a 2.5m
meter pole which takes the top of the aerial just above level with the
neighbouring houses roofs. It then feeds into the loft with about 3 M
of Y[1] cable, through a small lightening discharge unit (which I still
need to put the ground connection in for) and then through 3m meters
more of Y[1] cable. Then inside the loft room it goes into a panel
mount BNC connector and through 1M of RG-59/U cable before going into
the AOR AR900 scanner.

[1] It has no numbers written on it, but it is a 1cm diameter coax
cable
original bought for amateur radio use.

I suspect the loft room is fairly RF noisy as it is my study including
two computers, monitors, ADSL, wireless 802.11b etc. Connecting the
scanner to mains (via it's transformer, or battery makes no difference.

I'm looking for a rough idea of how much the following options would
improve my reception experience against the cost / difficulty of
completing those changes:

1) Change aerial (must also be able to Rx & Tx on 2m and 70cm)
2) Raise aerial by 1m or so, so that it is above neighbours roofs.
3) Change aerial feed cable
4) Ground the lightening arrestor (something I know I need to do
anyway)
5) Change Rx end BNC to BNC cable (is that the right kind of cable?
Impedance mismatch?)
6) Change panel mount BNC connector (does this let noise in due to
short unshielded bit of inner cable or impedance mismatch?)
7) Add a band pass filter for airband at the Rx end
8) Add a pre-amp for airband as close to the aerial as possible

Any other suggestions?

Thanks in advance
Kev



Just out of curiosity, you say the aircraft on the ground are noisy and the
tower too. Are aircraft in the circuit area ok and readable or are ALL
affected?
Silly question, but you are in AM Mode, aren't you?
The antenna you have is not designed for this frequency range, but ought to
work well enough as I am able to listen to aircraft on a similar
arrangement.
Further height will always help, especially as you want to hear ground
signals. It will make little difference with airborne signals.
If oyu are having trouble with ALL aircraft signals, then you really need to
consider relocating that antenna. Consider turning off some of that
equipment to isolate the possible noise source that may be drowning them
out.
If the signals are affected by local noise, a preamp will amplify that too.
Putting an airband preamp on won't allow you to use it for 2m and 70cm.
I don't understand the part about "short unshielded bit". None of the coax
or bnc plugs should allow you to have any "short unshielded bits" and might
be a starting point.
Grounding the lightning arrestor should make no difference to reception,
only offer protection in the event of a local discharge, and it won't do
much in the event of a direct hit, so don't place too much faith in it.

Brad.

Hi Brad

Thanks for the quick response. Yes I am in AM mode Aircraft on the
ground are barely readable, the Tower is slightly better but still I
can only make out 25% of what is said. In general flying aircraft are
better, with 25% being very clear, but equally 25% being worse than
the tower.

I will try turning everything off up here tomorrow and see if it makes
a difference reducing the electrical noise.

The aerial is on the chimney, so about the best position I can get it
other than on a longer pole on the chimney.

Pre-amp wise I could get it just where the coax comes in through the
roof tiles, and then I could take it out when I want to Tx.

The 'short unshielded bits' - it is a Panel Mount BNC Socket, so the
shield is twisted together and soldered to a lug on the outside,
leaving about 1cm of center unshielded.

Other option I thought off was to take a dedicated airband aerial,
soemthing like this:

http://cgi.ebay.co.uk/ws/eBayISAPI.d...tem=5773226141

and either place that high up in the loft space?

Thanks again
Kev

wrote in message
oups.com...

The 'short unshielded bits' - it is a Panel Mount BNC Socket, so the
shield is twisted together and soldered to a lug on the outside,
leaving about 1cm of center unshielded.

That part won't matter. I was more concerned with poor terminations in the
feedline.

That antenna on ebay doesn't specify a length, but looks like a similar
style to mine. That's certainly where the gain needs to be. If you really
want to receive that airport, you could consider a short yagi, 3el perhaps.

How far away is this airport? What terrain between your locations?
Brad.

wrote:

Aircraft on the
ground are barely readable, the Tower is slightly better but still I
can only make out 25% of what is said. In general flying aircraft are
better, with 25% being very clear, but equally 25% being worse than
the tower.

This is not an uncommon situation, I have encountered it in a couple of
places I have lived.
The tower transmitting antennas may very well be quite a distance from the
airport and if they are on the opposite side to you, or shielded by hills
of buildings you could very well have problems.
Aircraft on the ground will likely be often blocked by buildings.
Airborne aircraft will usually be in your line-of-sight and easy to hear,
but if they are low and on the far side of the field could pose a problem.

At my location I can hear most traffic at four airports:
One is very close and I can hear everything.
The others are some miles away and although I can hear aircraft until they
are quite low I loose them on final approach or on the ground. One tower is
very weak or inaudible. the other two just are not there.

Just because there are lots of antennas on top of the control tower, or
near by, does not guarantee they are the ones used for normal transmission.
Several towers I have worked in only use the antennas on the roof for
receivers or back-up transmission. the main transmitter site was usually
some distance away.

Dave

On 22 Oct 2005 11:06:03 -0700, said in
rec.radio.scanner:

I'm looking for a rough idea of how much the following options would
improve my reception experience against the cost / difficulty of
completing those changes:

1) Change aerial (must also be able to Rx & Tx on 2m and 70cm)

Not much change, since the antenna is really a random length (and a
short one) or wire at aircraft frequencies. Cost for a significantly
better antenna - significant.

2) Raise aerial by 1m or so, so that it is above neighbours roofs.

Not much difference. See below. Cost - relatively little.

3) Change aerial feed cable

Unless the cable is really bad, 7 meters of cable isn't going to have
too much loss at 100 MHz. Cost - relatively small.

4) Ground the lightening arrestor (something I know I need to do
anyway)

If a lot of your noise is from static on the antenna, this may help a
bit. Ground the antenna for a moment and see if the noise goes away
for at least a minute or two. Cost - almost none.

5) Change Rx end BNC to BNC cable (is that the right kind of cable?
Impedance mismatch?)

What's "BNC cable"?

6) Change panel mount BNC connector (does this let noise in due to
short unshielded bit of inner cable or impedance mismatch?)

What's the panel connector now?

7) Add a band pass filter for airband at the Rx end

Noise is broad-band - it's on the aircraft band too. Cost -
relatively high.

8) Add a pre-amp for airband as close to the aerial as possible

It'll probably increase the noise as much as it increases the signal.
Cost for a good one - very high.

Any other suggestions?

1) Be aware of what kind of system you're trying to receive. The
aircraft communications system is designed for 3 things:

a) air to ground communications
b) ground to air communications
c) air to air communications

One thing it's *NOT* designed for, except ar extremely close range, is
ground to ground communications. (The tower can see the aircraft on
the ground. Can you?) Unless you're within a km or 2 of the airport,
concentrate on receiving aircraft that are a) not too high up and b)
near you. Very few people have the equipment to DX aircraft signals.

2) Your receiver's AM detector may not be as good as an AM detector
can be.

Hi

'BNC Cable' = 1M of RG-59/U

The BNC Panel connector is still a panel connector, ie an open backed
soldered connector that does leave a short bit of unshielded core.

The airport is Sywell, about 5 miles away from me, a small local grass
airfield. I'm looking to hear this airfield well as I want to do my
PPL from there at some point soon. I will try and get a better idea
of the terain between Sywell and myself at the top of Wellingborough
later, but there certanily isnt a mountain between us

I'm thinking that a short Yagi might be the best bet for my situation,
as from what you guys are saying there is nothing terrible in my
current setup at the moment, and aircraft close to Sywell and the Tower
at Sywell is what I really want to improve if I had to pick a more
specific target to improve.

Comments & sugestions welcome.

Cheers
Kev

Looking around at Yagi's the largest selection is obviously for the
amateur bands. How much gain will I loose on airband from a 2M (144Mhz
ish) Yagi? Somehting like this maybe:

http://cgi.ebay.co.uk/ws/eBayISAPI.d...tem=5821390009

Cheers
Kev

wrote in message
oups.com...
Looking around at Yagi's the largest selection is obviously for the
amateur bands. How much gain will I loose on airband from a 2M (144Mhz
ish) Yagi? Somehting like this maybe:

http://cgi.ebay.co.uk/ws/eBayISAPI.d...tem=5821390009

Cheers
Kev

wrote in message
oups.com...
Looking around at Yagi's the largest selection is obviously for the
amateur bands. How much gain will I loose on airband from a 2M (144Mhz
ish) Yagi? Somehting like this maybe:

http://cgi.ebay.co.uk/ws/eBayISAPI.d...tem=5821390009

Cheers
Kev

The loss will be considerable. Yagis are quite narrow band. For a few
bucks/pounds/euros you can buy some aluminium tubing from a hardware store
and build your own.

If the countryside around you is reasonably flat, it makes sense that you
are having trouble hearing GA aircaft. The top mounted antennas are barely
5ft off the ground, the belly antennas merely 18" off the ground. That's not
a lot of antenna height. Most GA aircraft coms run less than 10W.

Brad.