Topic: Non-LR Mark III (400 mHz ) sensor package antenna mod to make it directional

[DaleReid]

I used to be able fiddle with some antenna stuff back when I recall much of the studying I did for my ham license, but haven't done much in decades.

I have a Rainwise Mark III, non LR (not the 2.8 gig but the 400 mHz range system) that is just on the hairy edge of getting to my display in the house. 

I'm thinking that the whip length sticking out of the bottom of the electronics case (one of the newer ones before they stopped making that model) is just a 1/4 wave dipole.

Has anyone successfully modified such a unit to make it accept a Yagi or some such to perhaps enhance the signal strength at the receiving end (and perhaps putting such a mod on the little receiver box, too)?

The solid wire whip screws into the transmitter board, so I have no idea how much of the design is loading of the transmitter and all, and no doubt the VSWR would be goofy, but it might be a fun little project.

Dale

[Vasco]

I have a Rainwise Mark III, non LR (not the 2.8 gig but the 400 mHz range system) that is just on the hairy edge of getting to my display in the house.

Most of my Oregon Scientific WMR200 sensors (433 MHz) are right on the hairy edge 

I'm thinking that the whip length sticking out of the bottom of the electronics case (one of the newer ones before they stopped making that model) is just a 1/4 wave dipole.

Hmm, 1/4-wave at 433 MHz is 17.3 cm (6.8"). . . 17.9 cm (7.1") at 418 MHz. Refresher course at https://en.wikipedia.org/wiki/Dipole_antenna

Has anyone successfully modified such a unit to make it accept a Yagi or some such to perhaps enhance the signal strength at the receiving end (and perhaps putting such a mod on the little receiver box, too)?

What does the receiver antenna look like? If it's just a stub you could try my totally non-scientific mod: one day I clipped a (roughly) 1/2-wave length of thin aluminium tube to the console antenna with a binder clip and I've never looked back. No electrical connection, just proximity. I unclipped it the other day out of curiosity and lost two sensors immediately: put it back and they reappeared.

Doesn't have to be aluminium tube, just thin metal: it's what I had lying around in the garage. . . You could try 1/4-wave, too: just experiment 

[DaleReid]

Thanks for the suggestion.  Secondary coupling as a try might be cheap and easy.  thx.  Dale

[Vasco]

I did find one sure-fire method of enhancing signal strength from my rain gauge, which is on a coping at one corner of the garage roof. To replace batteries in the WMR200 sensors you basically have to remove the sensor casing, change the batteries, push a reset button and then rush back indoors to set the console into "search" mode. If successful, you go back and replace the casing.

So one day, after having gone through all this rigmarole and put the ladder away, I noticed I had lost signal again. Up the ladder, dismantle, press reset, search. . . success! Reassemble, put ladder away - no signal.

Half-way through the third iteration the penny dropped. . . the aluminium ladder was acting as an extra antenna