Fox Hunting as SWL
This is to tell how couple of SWL got together and participated on Fox Hunt event on held by RSSL.
No ! we do not kill animals !
Some of you may think, oh well these people going to hunt live Foxes. No, not at all. Fox hunt is an event where radio researchers participate a friendly competitive event of finding a hidden radio transmitter, using various techniques and tools.
Train and prepare for emergency through fun
The intention in my opinion for the annual fox hunt activity is to keep radio researchers prepared for emergencies where radio location finding is needed. Search and rescue operation is something where it needs different skills and as much ass many people co-ordinating, yet attempting to reach fast as possible with multiple routes.
Think of a situation where an aircraft crashed onto the thick jungle. Arial survey may not find any trace. However most likely there will be a distress radio beacon active for days on the crash site. The fastest way to locate the crash site is by locating the radio beacon by radio location. This is why an interested radio researcher would keep the tools and skills updated by participating this activity.
Licensed HAMs and SWL
Radio researchers, who does not have radio transmission license on the public airwaves is called SWL (Short Wave Listener). There were times where only high frequency (HF)band is the highest band available for radio communications and broadcasting. So anyone who do research while not having transmission license were called Short Wave Listener. But there are much more activity on much higher bands these days.
The Fox Hunt was traditionally thought as an event where licensed HAMs participate and excels as they have the most knowledge and wealth of experience on adopting to varying situations.
RSSL generously allows SWLs to participate on the fox hunt event as it only requires one to listen or receive the radio signals. Couple of RSSL members who has not yet got license got together and though of forming all SWL team to compete for the event on 2019.
Preparation
We had initial discussion with the members, and came up with a strategy.
Had lot of advice and got past experience from an expert HAM Wije (4S7VJ)
Use RTL SDR With Laptop to receive the signal and compare signal strength
Build a portable VHF fox-hunt antenna using steel measuring tape [1]. This will help to find the general direction of the transmitter.
Build a magnetic loop antenna tuned to the fox hunt frequency to find out the sharp null. This will help to narrow down the signal path.
Wije also explained that it is very difficult to find the location when we are close to last 500m of the transmitter as the signal tend to reflected by any object nearby. Tips of using attenuator, and removing the antenna ans use a paper clip are tried and tested methods on this situation. However we did not have access to attenuator nor a transceiver. Therefore we thought of building a auxiliary antenna for third harmonic, which is in UHF band to pinpoint the fox when we are closer to the fox. link [2]. This has proven to work in the close proximity where the UHF band 3rd harmonic signal was really able to pinpoint the fix.
References
[1] Tape measure antenna http://theleggios.net/wb2hol/projects/rdf/tape_bm.htm
[2] Wije’s page with loads of knowledge: https://www.qsl.net/4s7vj/
