Question re VHF/UHF antenna?

[gleff]

Hi all,

I'm thinking of getting the following antenna for listening to the airbands on my scanner.

http://dpdproductions.com/page_miltenna.html#mtuvomni

I'm just wondering though.. If they have it tuned for two bands eg. UHF 225-400 MHz and 118-137 MHz Air, does that decrease it's signal quality for one or the other?

I live about 12nm away from the airport but i'm not line of sight.  Currently I'm using a Mag Mount Air band antenna (118-137 MHz) but my ground plane isn't good and I doubt I'm getting the signal I would normally get had I been using a proper ground plane.  I'm also using it indoors.  The result is that I'm unable to hear ground operations and the control tower.  I'm able to hear the ATIS pretty well, and the Director operations etc but I also get a lot of static, and it's pretty directional.  Even if I place the mag mount on the ground on the veranda, it's not much improvement.  I've been using a biscuit tin lid as the ground plane but I understand to be affective it needs to be at least one wave length in size which I believe is about 2 metres in diameter.  This isn't feasible for me hence my wanting to get a proper outdoor antenna that doesn't need a ground plane.

I'll be mounting this on my veranda.

Basically, I want to maximize my listening quality.  I want to hear ground operations, the tower, and aircraft, and I want it to be really clear.

Is this possible if they've tuned the antenna to two different frequency bands?  I only have about 1.5 metres of clearance so I can't get a proper VHF antenna.

What do you think my success will be with this antenna?

[Jeremy]

What you have should work OK. Groundplanes must not be less than a quarterwave radius. A buscuit tin lid should work.
Any outside aerial will work better than being indoors. As always, the higher the better.
The miltenns is a halfwave which gives a small amount of gain.
J.

[gleff]

What you have should work OK. Groundplanes must not be less than a quarterwave radius. A buscuit tin lid should work.
Any outside aerial will work better than being indoors. As always, the higher the better.
The miltenns is a halfwave which gives a small amount of gain.
J.

Do you think i'll notice any improvement though.  I realize the one I have *should* work but I don't think the biscuit tin lid is doing anything and it's frankly not that crash hot.

Also, back to the original question.. Does the fact they have it tuned for two bands have any effect?  Or would it be better to have something tuned ONLY for the VHF Air band?

I really want to hear clear communications and ground operations etc but I just can't do it with what I've got.  Maybe it's just a crap antenna, or maybe it's just my location.  It doesn't need to be line of sight does it?

Incidently, wouldn't a 1/4 wave of 130 MHz be about 22 inches?  This biscuit tin lid wouldn't be more than about 6-8 inches.

[Jeremy]

re tin lid - For receiving purposes I do not think it will make much difference. The aerial being tuned for 2 bands should be OK. I am guessing but a half wave at 100 Mhz is a fullwave at 200 Mhz so in theory, will be resonant.
VHF/UHF is line of sight so try moving the aerial around and get it as high as you can.
J.

[gleff]

Hmmm.. In that case maybe it's a pipe dream for me to expect to hear nice clear communications because i'm not able to get a lot with the current antenna no matter where I put it.  I was hoping the other antenna would show an improvement. 

I might get it anyway just to give it a whirl though.

[Jeremy]

If you specifically only want to hear your local airport then you could try a beam antenna. However, if there is a hill in the way then nothing will work.
J.

[Canonjohns40D]

Hi Gleff

I live in Northern Ireland  and I bought this aerial and indeed their one for the radarbox, both roof mounted. I have found both excellent quality in the build and impressive in their usage.

I can hear aircraft on both civil and Mil frequencies that previously were out of range. However as Jeremy says the location of the airport is a factor. I loose flights into my local George Best BHD but only when they change to the tower frequency and are very close to landing. This as arresult of them being behind a hill. i hope this helps a little Dave at DPD was very good and the service was excellent.

John

[orkney]

if there is a hill in the way then nothing will work.
J.

hello

there is a hill between us and the airport 10nm away and although not too clearly I can hear aircraft on the ground and the tower atc so I do think it is worth trying to listen if there is a hill.

Andrew

[Jeremy]

Oh. I thought you could not hear them. In that case any external aerial will improve reception and get it up as high as possible.
J.

[gleff]

It's not actually a hill obstructing my view.. it's the fact I live on the 13th floor of an apartment building (which I'm about 20 metres off the ground), but unfortunately facing the opposite direction to the airport.  There's also one other building blocking the view.  Apart from that though, it's about 12nm away and generally clear.

I can pick communications up, but there's a fair bit of static and directional.  I however can't hear the ground or most Tower comms.

I'll give this some further thought.

[VK2GEL]

Gday Geoff, yes it's 22" and I think a quarter wave radius ground plane is also correct. With a magmount, the outer coax braid is not earthed to the groundplane, so try a proper vehicle 'through metal' mount that will earth the radio to the ground plane. You can solder bikkie tins. Before spending big on a commercial, I would build a cheap beam and try swinging it around on a tripod pointing at buildings for reflections until you get best results, and maybe try a filter/preamp as AM is a terrible mode for interference in the city:

http://www.liveatc.net/forums/listener-forum/airband-yagi-antenna-designs/

http://matchmaster.com.au/_product_37002/09MM-FMTP about $7, available from at least http://www.salmonbros.com.au/custompage.aspx?custompage=Store%20Locations and http://www.jrt.com.au/branch-locations/

http://ssejim.co.uk/21-airband.htm

http://www.garex.co.uk/vhf_accs/vhf_accs.htm

http://www.scannermaster.com/Filters_s/39.htm

and if you're really serious http://www.parelectronics.com/scanner.php and http://www.stridsberg.com/prod02.htm

[gleff]

Hi Grant,

Thanks for the email and the above info.  I've decided to hold off on the VHF antenna for the time being.  I was playing around with the mag mount last night and did manage to have a bit of success.  When I put it on my veranda in the corner I can pick up some pretty clear communications.  It's still pretty crap for the Tower and Ground but all the rest is a lot better than it was.  I might experiment further before making any decisions to get another one.

Incidently, I noticed you're in Aus as well..  I'm reallllllllly bad at making antenna masts/brackets and could do with some suggestions.  While I'm going to put my VHF antenna purchase on hold, I'm still serious about purchasing a new ADS-B antenna (see my other thread).  My current antenna is mounted like this since I live in an apartment.  http://www.gleff.com/1a.jpg

I didn't make that bracket but I need to come up with something similar but for an antenna that is 1 1/4 inches in diameter.  Can you suggest anywhere in Aus (preferably Sydney) where I can buy something ready made. 

I essentially want to mount the http://dpdproductions.com/page_vhf_air.html#adsbout on my balcony like the other one.  I went to the hardware store today but couldn't find squat, and even if I had, I wouldn't be any good making anything. (oh how I wish I paid more attention in shop class LOL).  I need to be able to mount it on a horizontal pole like the above.