Awhile back, there was a thread about field intensity meters for AM. Maybe this link is posted somewhere else here, but I haven’t noticed it. So if you are interested in making your own, check out this cool web site by David Forsman, WA7JHZ. You’ll need to scroll down the page a bit until you come to the “Test Equipment” section, where you’ll find the EMF Intensity Meter project– designed for use in the 0.54 to 1.70 MHz band! Also check out the other nifty projects, including a 160 meter AM QRP transmitter that could easily be modified for Part 15 use on the AM band.
Here’s the link: http://myweb.cableone.net/adamsmed2/catalog.htm
FI Meter
Hi, WEAK
Looks good in general, but probably would be hard to calibrate so as to display the real field strength accurately.
The description for it suggests that it can be calibrated 5 wavelengths from an AM broadcast station of known power, having a 1/4-wave tower. But how would the actual field strength there be known unless it was measured by a calibrated, professional grade FI meter?
Maybe best to consider this meter as an indicator of relative field. It would be useful to determine when radiation from a Part 15 AM setup was maximized, but not so much to measure that value in absolute terms — such as would be needed to show compliance with 15.209, for example.
Rich
Calibration is difficult
Rich–
I wouldn’t expect an average hobbyist to be able to satisfactorily calibrate this device. They most likely would not have the expertise or the equipment to do so.
I see it mainly as a tool to help assess the relative effect of changes to the radio system’s performance; either intentional, such as adding ground wires; or unintentional, such as weather-induced variations.
Some very rough signal level calibration relative to another station might be possible. For example, you could determine at what distance your Part 15 station has about the same strength as that station.
On the other hand, if someone had a friend who worked at a local station, perhaps that person might let you accompany them the next time they are taking their monitor point measurements. You could then compare your readings to those taken on a professional instrument.
WEAK-AM
Classical Music and More!
Another Meter Post, LP/MedFer SWR
Here are some photos of a low power, low frequency SWR meter for antenna tuning in the Medium Wave band.
Sorry, no schematic available yet…
Click on any photo for a larger image.
Experimental broadcasting for a better tomorrow!