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General Radio Discussion / 49 MHz Range Testing Part 15 Experimentation
« on: September 29, 2019, 1508 UTC »
I picked up a pair of Maxon PC-50 5 channel 49MHz band FM transceivers (they’re actually made by Midland apparently). These radios are very similar to the Radio Shack TRC-512 and TRC-503 5-channel FM walkie talkies - same channel plan, same circuit board, etc. The Maxon radios have removable antennas (!!) and, of course, they’re rubber ducks.
I did some basic range testing with the stock antennas and got about 90-100 meters away before the signal started dropping out. I replaced the rubber duck on one with a 50-foot piece of wire and the range went up to 400 meters (1300 feet, around 1/4 of a mile) before the signal started dropping in and out. This is in a heavily built up area too. I used 49.875 MHz as it appears to be the less-used of the 49 MHz frequencies. The Maxon and RS radios use a standardized channeling plan,
Channel A - 49.830 MHz
Channel B - 49.845 MHz
Channel C - 49.860 MHz
Channel D - 49.875 MHz
Channel E - 49.890 MHz
But my research indicates there is no official channel plan, only the band limits per Part 15: 49.820 MHz - 49.900 MHz. Commercial/consumer equipment is limited to 10,000 microvolts per meter at 3 meters. Baby monitors use random channel plans, often with 2 channels - 49.850 MHz and 49.870 MHz are popular pairs, as are 49.835 MHz and 49.865 MHz. Yes, they are still making regular 49 MHz FM baby monitors today, most of them are 2 or 3 channel units...again with arbitrary channel plans (49.830 MHz, 49.850 MHz, 49.870 MHz seems to be pretty common too).
I’ve driven around with my scanner and have noticed three different open mics/baby monitors within a mile radius of my house on 49 MHz. Two of them are on 49.830 MHz and the other is on 49.860 MHz (it sounds just as strong on 49.865 MHz, however...maybe it’s closer to 49.8625 MHz?). The 49.860 signal is strongest in the downtown central business district away from residences and doesn’t have background noise and people talking like baby monitors do. It’s not a birdie, multiple radios hear it....and it has the range you’d expect from a 49 MHz monitor transmitter...
One of the 49.830 MHz ones carries a pretty impressive distance, and this is with a scanner and an antenna tuned for 150 MHz. Side by side comparisons between the Maxon 49 MHz walkie talkies and the scanner show that these little HTs have excellent sensitivity.
I plan on replacing the stock rubber ducks with telescopic whips and maybe getting a pair of RadioShack TRC-512 49 MHz radios, since they come with telescopic whips that could easily be upgraded.
The rules also state that while consumer gear is limited to the 10,000 microvolts/meter at 3 meters...hobby or home built equipment can transmit up to 100mw (measured at antenna terminals at the highest level of modulation) on any frequency within the 49.82-49.90 MHz band using any modulation type as long as it stays within the band. Certainly a beacon opportunity there.
Anyway, I see equipment on this band as serving a niche communications need. FRS radios, MURS, and other VHF/UHF bands (even handheld CB radios) carry a lot further than these 49 MHz rigs do. Cheap intra-squad radios for militia types maybe?
I did some basic range testing with the stock antennas and got about 90-100 meters away before the signal started dropping out. I replaced the rubber duck on one with a 50-foot piece of wire and the range went up to 400 meters (1300 feet, around 1/4 of a mile) before the signal started dropping in and out. This is in a heavily built up area too. I used 49.875 MHz as it appears to be the less-used of the 49 MHz frequencies. The Maxon and RS radios use a standardized channeling plan,
Channel A - 49.830 MHz
Channel B - 49.845 MHz
Channel C - 49.860 MHz
Channel D - 49.875 MHz
Channel E - 49.890 MHz
But my research indicates there is no official channel plan, only the band limits per Part 15: 49.820 MHz - 49.900 MHz. Commercial/consumer equipment is limited to 10,000 microvolts per meter at 3 meters. Baby monitors use random channel plans, often with 2 channels - 49.850 MHz and 49.870 MHz are popular pairs, as are 49.835 MHz and 49.865 MHz. Yes, they are still making regular 49 MHz FM baby monitors today, most of them are 2 or 3 channel units...again with arbitrary channel plans (49.830 MHz, 49.850 MHz, 49.870 MHz seems to be pretty common too).
I’ve driven around with my scanner and have noticed three different open mics/baby monitors within a mile radius of my house on 49 MHz. Two of them are on 49.830 MHz and the other is on 49.860 MHz (it sounds just as strong on 49.865 MHz, however...maybe it’s closer to 49.8625 MHz?). The 49.860 signal is strongest in the downtown central business district away from residences and doesn’t have background noise and people talking like baby monitors do. It’s not a birdie, multiple radios hear it....and it has the range you’d expect from a 49 MHz monitor transmitter...
One of the 49.830 MHz ones carries a pretty impressive distance, and this is with a scanner and an antenna tuned for 150 MHz. Side by side comparisons between the Maxon 49 MHz walkie talkies and the scanner show that these little HTs have excellent sensitivity.
I plan on replacing the stock rubber ducks with telescopic whips and maybe getting a pair of RadioShack TRC-512 49 MHz radios, since they come with telescopic whips that could easily be upgraded.
The rules also state that while consumer gear is limited to the 10,000 microvolts/meter at 3 meters...hobby or home built equipment can transmit up to 100mw (measured at antenna terminals at the highest level of modulation) on any frequency within the 49.82-49.90 MHz band using any modulation type as long as it stays within the band. Certainly a beacon opportunity there.
Anyway, I see equipment on this band as serving a niche communications need. FRS radios, MURS, and other VHF/UHF bands (even handheld CB radios) carry a lot further than these 49 MHz rigs do. Cheap intra-squad radios for militia types maybe?
