Hi there
I am a (poor) wildlife researcher and I am trying to re-pot (replace batteries) in small wildlife VHF tracking collars (tone beepers); however, I have a problem. I have replaced the batteries using the exact same brand and type Fujitsu CR1/3N, the problem is the transmission strength is no where near as strong as what they used to be. Strangely though if I touch the battery with my fingers, the transmission strength is very good. Could someone please explain to me why this is so and a possible solution to increase the transmission strength.
Many thanks
Cam

 

Hi there
I am a (poor) wildlife researcher and I am trying to re-pot (replace batteries) in small wildlife VHF tracking collars (tone beepers); however, I have a problem. I have replaced the batteries using the exact same brand and type Fujitsu CR1/3N, the problem is the transmission strength is no where near as strong as what they used to be. Strangely though if I touch the battery with my fingers, the transmission strength is very good. Could someone please explain to me why this is so and a possible solution to increase the transmission strength.
Many thanks
Cam

This sounds like a broken connection. I presume that the collar itself has an embedded conductor (wire), which is the loop antenna for the transmitter. I further assume that for the purpose of durability 'in the wild', you need to repot the batteries with epoxy potting compound. If these presumptions are correct, then spent batteries will need to be physically dug out of their epoxy embedding using considerable physical force. It is likely that during this process one of the two connections to the loop antenna broke off. What you are left with is a monopole antenna with a grossly inadequate ground plane. By physically touching the battery your body acts as the ground plane. In equivalent terms, your body together with the monopole make up a dipole antenna. This explains the improved transmission range.

As far as solving this problem is concerned you will need to obtain the physical layout of the resin encapsulated PCB to know where the connections to the loop antenna are. Then its simply a matter of scraping off the gunk and checking the connection continuity with a multimeter.

EDIT: Look at section 2.1.1 in this: http://www.ericlwalters.org/telemetry.pdf

 

This sounds like a broken connection. I presume that the collar itself has an embedded conductor (wire), which is the loop antenna for the transmitter. I further assume that for the purpose of durability 'in the wild', you need to repot the batteries with epoxy potting compound. If these presumptions are correct, then spent batteries will need to be physically dug out of their epoxy embedding using considerable physical force.

OK so far - but I tend to use wax for things I'll need to get apart again at some point.

Altar candles are a decent weight of wax for a not too bad price.

 

OK so far - but I tend to use wax for things I'll need to get apart again at some point.

Altar candles are a decent weight of wax for a not too bad price.

Will candle wax stand up to sharp animal teeth attempting to bite off the pesky collar, or to fights over food/sex/territory, or to being scraped against the ground or vegetation, or being soaked in rain-, lake-, river-water ? Life as an animal telemetry transmitter is as tough & brutal as the lives of the wild animals themselves.

Mind you, you may well be right, as the OP hasn't specified the potting compound used. But IMHO wax would be a poor choice for the reasons I have given above.

 

Will candle wax stand up to sharp animal teeth attempting to bite off the pesky collar, or to fights over food/sex/territory, or to being scraped against the ground or vegetation, or being soaked in rain-, lake-, river-water ? Life as an animal telemetry transmitter is as tough & brutal as the lives of the wild animals themselves.

.

Its pretty difficult to pot anything that isn't in some kind of container.

 

This sounds like a broken connection. I presume that the collar itself has an embedded conductor (wire), which is the loop antenna for the transmitter. I further assume that for the purpose of durability 'in the wild', you need to repot the batteries with epoxy potting compound. If these presumptions are correct, then spent batteries will need to be physically dug out of their epoxy embedding using considerable physical force. It is likely that during this process one of the two connections to the loop antenna broke off. What you are left with is a monopole antenna with a grossly inadequate ground plane. By physically touching the battery your body acts as the ground plane. In equivalent terms, your body together with the monopole make up a dipole antenna. This explains the improved transmission range.

As far as solving this problem is concerned you will need to obtain the physical layout of the resin encapsulated PCB to know where the connections to the loop antenna are. Then its simply a matter of scraping off the gunk and checking the connection continuity with a multimeter.

EDIT: Look at section 2.1.1 in this: http://www.ericlwalters.org/telemetry.pdf

Cheers Sitara
Yep, the + wire was excessively long and may have functioned as a dipole loop. As it loops does the loop have to be insulated against each other where they cross ? Indeed the epoxy was like a rock even when using a heat torch. I have a feeling that the excessive heat used my have contributed to the problem as well as the forced effort. In the meantime I have an idea about how to avoid this and I will let you know how it goes. But yes if the loop is not insulated where they cross and touch each other does that pose a problem?
Cheers
Cam