My club, Newport County Radio Club (NCRC), held a dry run for fox hunting tonight in a local park (a beautiful ocean-side park, on a stunning RI summer afternoon I will add). We wanted to try out several different antennas and approaches to RDFing.
We were using three MicroFox15 transmitters (15 mW output) hidden not far away and noticed that even at that low transmit power, when we got to within 30 feet of the transmitter, we were no longer able to discern any bearing information — the signal was equally strong 360 degrees around.
Two things could cause that. First is simply so much RF going into the antenna jack — so much so that even a 20-30 dB front-back difference in the antenna would not be noticeable (external attenuators would help in this case). The second possibility is that the HT itself is so poorly shielded that RF is getting directly into the radio electronics through a path other than the antenna jack.
I ran a simple experiment tonight with three different HTs by removing their antenna. I measured the distance from the MicroFox15 to where the squelch opened up (I will call that a “S1” signal), as well as the distance when I was getting “full bars” of signal strength (A “S9” signal):
S9 S1
BaoFeng UV5R 15 feet 20 feet
BaoFeng UV82 12 feet 15 feet
Kenwood TH-D72A 1 foot 5 feet
Why is that significant? It says that the inexpensive UV5R radios, something my club gives to new hams who join, isn’t as well shielded as it could be. If it has a S9 signals at 15 feet with no antenna, then no RDF antenna is going to help discern direction. But it looks like it should be usable at 20 feet.
The slightly newer UV82 model is a bit better. But a real significant difference can be seen in my Kenwood TH-D72A — I would expect it could be used to get within 5 feet of the fox.
This won’t be a concern far out, but close in, where you need to be to find the tiny MicroFox15 transmitter, requires some shielding considerations.
