Best antenna mod?

[Spider-Vice]

Basically, the story is always the same with the Fine Offsets. Have a FO that works perfectly for a while (could be a month, could be whatever) and then out of the blue it just stops working well and only intermittently, only to work fine in another location for like 10 hours and come back to its stupidity. I already have an antenna mod on mine, which is basically a cable from an old wireless adapter, and it works very well and is a huge upgrade on the original one, but having two/three whole floors above me, it can get hard for it to capture the signal correctly.
It is God damned puzzling how it can be working in a location of the house, correctly and constantly for so long, and then just stop working out of the blue, only to function somewhere else and stop working there too, especially when it is windy, which is extremely weird! An issue with my antenna mod is that moving the cable a little immediately influences signal as well, so my question is, what would be the best kind of antenna mod to create? Dimensions of cable, methods, if I should also mod the transmitter antenna, etc. as I am not really a radio signal savvy person! It is the 868.3 Mhz version.

PS: Batteries on transmitter are fine, even after replacing performance can be erratic. It is definitely not the wind, the mast and the radiation shield I made for the station (where the transmitter is) are perfectly stable and do not sway even with human hand-force.

Thanks in advance!

[Areco747]

Hi, This is our best result, a 433 Mhz antenna built into the display, reaching a range of 300 meters (from the display to the external sensor) http://medicion.mforos.com/1923191/1122 ... wh-ws1081/ http://www.meteostar.com.ar

[Spider-Vice]

That actually looks pretty nice. I had tried a similar thing but mine wasn't working very well, probably because I just had the antenna itself. But unfortunately, mine is the 868.3 Mhz version, unless something like that works too.

[AllyCat]

Hi,

... stop working out of the blue, only to function somewhere else and stop working there too, especially when it is windy,

A common problem with UHF radio signals (i.e. 433 and 868 MHz) is caused by "multipath reception". The signals can "bounce" off various objects, so the receiving antenna "sees" not only a signal "line of sight" from the transmitter (or it may not see that one at all) but via one or more (longer) indirect paths. If the path lengths differ by "half a wavelength", it's possible for the signals to "cancel out" and the receiver sees nothing.

At 868 MHz, the wavelength is about 34 cms so moving either the transmitter or receiver antenna (or whatever object the signal is bouncing off) by just a few cms can be sufficient to cause the signal to "fail" (or to recover). The usual solutions are to ensure good "line of sight" transmission, that the transmitter has sufficient power and/or to use "diversity reception" (two or more antennas at slightly spaced locations, with duplicate receivers deciding which is the best signal). But none of these solutions are really practical for many FO stations.

having two/three whole floors above me, it can get hard for it to capture the signal correctly.

Note that most antennas are directional, in the case of the "vertical whip" (like you show) it receives fairly uniformly in all horizontal directions but has a "null" in the vertical direction. So if your transmitter is mainly "upwards" then the whip should be horizontal (the antenna in the FO Console is basically just a piece of wire bent around inside the case, so the directionality is difficult to predict and mainly a matter of "pot luck").

The length of the whip (technically called a monopole antenna) should be about a "quarter wavelegth", i.e. about 8 cms for 868 MHz. The 434 MHz antenna shown is probably less than 17 cms long because of the "curly bit" in the middle (technically called a "loading coil"), or it might just have been done to "look good".

You might always have reception issues if you have a bad signal path (or some form of local interference), but the best antenna I can suggest to try is a "dipole". Basically, two quarter-wave rods in-line, with a small gap at the centre, one rod connected to the "live" antenna input, the other to the "earth". The rods need to "point" at 90 degrees to the direction of the transmitter. Refinements could be to use a "folded dipole" and/or a "reflector". Take a look at the construction of most terrestrial TV aerials, although a "miniature" (scaled) version of a good commercial "FM radio" antenna might be a better guide.

However, antenna theory is very complex and ultimately it often becomes a matter of "trial and error". But that is VERY difficult in the presence of multipath effects, particularly with the FO transmitter which sends only a brief pulse of data every 48 seconds. Also, the receiver only reports "lost contact" after 8 consecutive "missing" transmissions, so you need to ensure that you have constantly changing data and to look for these changes every 48 seconds.

Cheers, Alan.

[Werk_AG]

Hi, This is our best result, a 433 Mhz antenna built into the display, reaching a range of 300 meters (from the display to the external sensor) http://medicion.mforos.com/1923191/1122 ... wh-ws1081/ http://www.meteostar.com.ar

I only can say that those antennas are really good for 433Mhz. Not only to receive but also to transmit.

[philcdav]

Hi guys.

have a look for previous posts that feature directional aerials.

The cheap and cheerfull cardboard/foil REFLECTOR gives directional gain for pennies and 20 minuts of labour