Touching the Antenna Cable?

[nigelpull]

I have a cheap antenna bought from Amazon that sometimes performs really well and then very poorly. Seems to be when the cable is moved about, but I don’t think it is a bad connector. Sometimes just touching the cable will cause the messages per second to go up, and letting go causes it to go down.

I have it mounted inside on a window mullion and it is connected to the Pro Stick Plus and connected to a RPi Zero W.

Is there a trick to getting better reception that I don’t know? Could there be an impedance problem? Is a better antenna recommended?

[KB4ERT]

What is the window mullion made of? Plastic, aluminum, steel? That type of antenna needs a ground plane under it. A metal can, metal cookie can lid, a steel pie plate works also. If the mullion is plastic or aluminum, then any scrap piece of sheet metal (preferred) would work. Those antennas are notoriously bad to start with, so shop around for something better. A homemade “spider” antenna works well also.

Three Easy DIY Antennas for Beginners

NOTE: Those who dont want to make a DIY antenna, can order Flightaware’s antenna from Amazon http://www.amazon.com/gp/product/B00WZL6WPO STARTER When DVB-T Dongle is purchased, a whip antenna is supplied with it. Every beginner uses this whip in his starter setup. Improve the performance of this whip antenna by three simple steps given below: (1) Whip is too long for 1090 MHz. Cut it to 67mm. (2) Magnetic base provides an insufficient ground-plane. Enlarge ground-plane by placing the whip …

[LawrenceHill]

@nigelpull

I have it mounted inside on a window mullion

You say you have mounted it on the window mullion, that is the vertical beam.
Does this mean the antenna is mounted horizontally?
Can you post a picture of your antenna installation?

[wiedehopf]

@nigelpull

I have a cheap antenna bought from Amazon that sometimes performs really well and then very poorly.

Could also be a HDMI monitor being switched on and off.
Some HDMI cables cause massive interference.

[nigelpull]

The window is a large aluminum storefront type (I am on the fourth floor). I experimented with the antenna on the middle mullion, about 3 feet off the ground, in a couple of locations, but the best place I have found is on the bottom mullion at the floor and near the corner as in the photo. I am using a square of hook and loop to fasten it down. Currently I am getting 50-125 messages per second (seems to hover around 80 most of the time). The window faces NE towards PIE, TPA, MCO, and a bunch of others within 100 NM, but generally I get only about 50 NM out (sometimes a little further).

Some kind of antenna with a suction cup mount bracket that I could attach to the window would be ideal…

[wiedehopf]

@nigelpull

Currently I am getting 50-125 messages per second

You’re feeding interference from the SDR / pi directly into the antenna.

The coax should not be squished.
Place the antenna on an empty food can and further away from the RPi.
Or at least move the antenna further away from the RPi / SDR.

Aslo if you don’t want to use a food can, at least set it directly on the window sill instead of putting something in between?
The base is magnetic and meant to interface with a metal surface.
Together you get a so called quarter wave ground plane antenna.

Also the antenna likely isn’t optimized for ADS-B, often it helps to unscrew the whip and replace it with a short wire.

How to improve performance of whip antenna of DVB-T

@nikka93 Here is a photo of the whip antenna modified as described by @geckoVN . This one uses a thin steel tie wire, not a copper wire, but both steel & copper are OK. Important thing is the wire should be thin so that it’s few turns can be easily wound on threaded stub. [Optimized-Whip-Steel-Tie-Wire]

[abcd567]

Place the antenna over an iron/steel food-can on floor besides the Window. The floor in photo seems to be only few inches below the window mullion, so if you use a tall enough food-can, it will keep the whip at window glass level.

The magnetic base of antenna will cling to the steel/iron food-can without the stuff you are currently using to hold the antenna in place on the aluminum mullion. That stuff may be the reason of poor grounding of antenna base.

[LawrenceHill]

@nigelpull

but the best place I have found is on the bottom mullion at the floor

That’s a transom, not a mullion but that’s good.
At least it is mounted vertically.

[abcd567]

Do NOT cut the whip. Unscrew it, and use a thin wire as whip. You may use a thin steel tie wire or one of the wires in a scrap network cable.

If the wire is thin, it will be easy to wrap it over the threaded brass stud of the magnetic base. With thick wire it is a bit difficult.

[nigelpull]

Man, I should know that; work for a contractor! Thanks!

[nigelpull]

Oops… already cut it! Was long enough before the spiral. I have some thin steel wire I can try too.

[abcd567]

Equally important to proper whip length is placing the magnetic base directly over a steel or iron food-can or plate. Electrically an aluminum plate will do, but as magnet will not cling to it, the whip will keep on falling frequently. Adding something non-metallic between base of antenna and aluminum will hamper grounding. Using a plate or can made of iron/steel will overcome this problem.

[dongerrard204]

As others have indicated, adding a decent ground plane (tin can etc) will bring improvements.
Based on photo of antenna placement, I would suggest moving antenna further to the left so its not so close to the metal window frame. This current location has the antenna somewhat hidden from signals to the right side of the view.

And as others mentioned, moving the pi & SDR below and further away from the antenna will reduce interference.

If you see improvements with these few suggested tweaks, definatley consider that for the cost of a purpose built antenna from Flightaware + appropriate coax cable and possibly an adapter, greater range and higher message counts are easily attained ( …once you read about adjusting the gain setting “down” due to the much higher sensitivity of the Flightaware antenna ).
Your stated 4th floor location will certainly help with your ADS-B spotting.
Cheers!

[timothydykstra82]

@wiedehopf

Could also be a HDMI monitor being switched on and off.
Some HDMI cables cause massive interference

Can you recommend a specific brand or type of HDMI cable? I notice massive signal level changes whenever my living room TV turns on or off.

[wiedehopf]

@timothydykstra82

Can you recommend a specific brand or type of HDMI cable?

No i can not.

Increase the distance to the TV …
Other than that cables that include ferrite cores might be better … not sure if there are any for HDMI.
Other than that i guess it’s trial and error.

[foxhunter]

@abcd567

directly over a steel or iron food-can or plate

Or a cookie can. The flavor or brand of the cookies is not important at this point.

SCNR, just reminds me on a discussion we had here almost two years ago

[abcd567]

@foxhunter

Or a cookie can. The flavor or brand of the cookies is not important at this point.

For him, it is.

[nigelpull]

OK, I’m getting a craving now for cookies.

Going to set a couple of goals to perhaps raise the bar a bit. First, get an enclosure for the Pi and the Prostick; more for aesthetics than anything else, but it might allow for a better mounting location. Wish I had a 3D printer (https://www.thingiverse.com/thing:4257443) but a plastic box should do nicely. Doesn’t need to be watertight.

After that will be to build a coaxial collinear antenna in some PVC or other tubing, add some suction cups, and stick it to the window. A lot of people have provided tutorials for this, present company included, and I have a soldering iron, loads of coax, some electrical tape, and a little time.

And a side note, after looking at the stats. At my old place, when I was moving out, I disconnected all my computer stuff, but left the PiAware running for a couple of days, just strewn across the floor with the antenna in the window. Without all the electronics interfering, and no change to the antenna position, there was quite a spike!

[smithers1962]

@nigelpull

Wish I had a 3D printer

Which country do you live in?
I can print you this enclosure if you want me to, no charge apart from postage, but I am in Australia, maybe someone who is closer can do the same?

[nigelpull]

That is very generous, thank you! I will send you a message.