Before we had antenna analysers or even VSWR bridges, amateurs often used small light globes to do antenna tests. Common checks involved measuring antenna current and field strength. After all the aim is to radiate the maximum signal for your output power and antenna arrangement.
And there's something solid about doing tests with a field strength meter, especially a passive type where it's only energy from your radiated signal that is driving the meter movement. While basic field strength meters give only a relative indication, even this is useful when you are just aiming for a peak in the radiated signal. Radio direction finding is another use for field strength meters, especially if you are very close to the signal source.
Unlike absorption wavemeters, field strength meters are not frequency selective. They can respond to signals on a wide range of frequencies. This means that you need to be mindful of strong local signal sources. For example there is a possibility that your meter could respond to stray RF if there is a nearby radio or TV station. Bear that possibility in mind if you see readings that don't make sense.
Anyway here are a selection of RF field strength meter circuits.
Wide dynamic range field strength meter Good discussion by KA7OEI
Simple field strength meter Andy Collinson describes one with just 4 parts
No Fibbin RF Field Strength Meter Described by VE7NI in QST
Sensitive RF Field Strength Meter Video by ElectronicsNmore
PS: Want to read more about antennas? Consider this selection of antenna books. They are affiliate links meaning that I receive a small commission (at no extra cost to you) if you decide to purchase.
And there's something solid about doing tests with a field strength meter, especially a passive type where it's only energy from your radiated signal that is driving the meter movement. While basic field strength meters give only a relative indication, even this is useful when you are just aiming for a peak in the radiated signal. Radio direction finding is another use for field strength meters, especially if you are very close to the signal source.
Unlike absorption wavemeters, field strength meters are not frequency selective. They can respond to signals on a wide range of frequencies. This means that you need to be mindful of strong local signal sources. For example there is a possibility that your meter could respond to stray RF if there is a nearby radio or TV station. Bear that possibility in mind if you see readings that don't make sense.
Anyway here are a selection of RF field strength meter circuits.
Wide dynamic range field strength meter Good discussion by KA7OEI
Simple field strength meter Andy Collinson describes one with just 4 parts
No Fibbin RF Field Strength Meter Described by VE7NI in QST
Sensitive RF Field Strength Meter Video by ElectronicsNmore
PS: Want to read more about antennas? Consider this selection of antenna books. They are affiliate links meaning that I receive a small commission (at no extra cost to you) if you decide to purchase.
Hello Peter, I got the field strength meter idea from your website at the first place. Here some more interesting links:
ReplyDeletehttps://pe4bas.blogspot.com/2014/08/field-strength-meter.html
You forgot your own website!
http://home.alphalink.com.au/~parkerp/gateway/noapr97.htm
A simple old diagram, I used it for a FSM in my magloop tuning box. The FSM is excellent as indicator for tuning a magloop antenna:
https://topbandchordalhopper.blog/2017/09/23/the-ky6r-field-strength-meter/
This QRPguys kit will be build here this year hopefully, I already purchased it.
https://qrpguys.com/qrpguys-digital-field-strength-meter
73, Bas
Many thanks Bas - some great links there!
ReplyDelete