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Author Topic: 49 MHz Range Testing Part 15 Experimentation  (Read 295 times)

Offline R4002

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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 (theyíre 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, theyíre 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).

Iíve 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 itís closer to 49.8625 MHz?).  The 49.860 signal is strongest in the downtown central business district away from residences and doesnít have background noise and people talking like baby monitors do.  Itís not a birdie, multiple radios hear it....and it has the range youíd 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?

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Offline Σ

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Re: 49 MHz Range Testing Part 15 Experimentation
« Reply #1 on: September 29, 2019, 1643 UTC »
You might want to add a BNC connector (or SMA if there is limited room on the case) so you can change your antenna easily.

When the 49 MHz walkie talkies were being sold there were a lot of hams who moved them up to 6m.   http://www.redwaveradio.com/2_6a1eac5ceba0ffdb_1.htm    I think it was more for fun than for being actually useful. One guy got crystals to hit the local 6m repeater because he was close enough. You can also make a nice little propagation beacon out of them with a keyer... once we get some propagation again. ;)   https://www.blackcatsystems.com/rf-products/ham_amateur_radio_beacon_cw_keyer_kit.html

You are almost better off finding some older Motorola MT1000 HTs if you want to have any comms with decent distance. If you are OK with measuring your range in feet then the Maxon/Midlands would do fine. There are a number of people I know who regularly use the business freq in that range for personal comms. They were smart and listened to the freq they chose for months and months before programming their radios. No interference complaint, no problems.

Many of the prepper squads have standardized on the Baofeng UV-5Rs as they have low power UHF for "intra-squad" as well as VHF for other uses. A scanner running close call defeats all attempts to hide your comms anyways. You can turn on the scrambler for casual eavesdroppers but that's all it will do. And some groups are using the spread spectrum 900 MHz Motorola HTs, too.
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Offline ThaDood

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Re: 49 MHz Range Testing Part 15 Experimentation
« Reply #2 on: September 29, 2019, 1850 UTC »
I can't decide upon what's worst, young and stupid, or old and chemically dumbed down.

Offline Σ

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Re: 49 MHz Range Testing Part 15 Experimentation
« Reply #3 on: September 29, 2019, 1902 UTC »
I've been on the Yahoo group for years... not much activity unfortunately.
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Offline R4002

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Re: 49 MHz Range Testing Part 15 Experimentation
« Reply #4 on: September 29, 2019, 2118 UTC »
Iíve browsed through the Yahoo group and the UK guys on transmission1.  Seems like the Maxon PC-50 and Radio Shack 5 channel HTs were sold in the UK and well.  Seems like they werenít very popular over there though. 

Iím thinking about either swapping the antenna connector for SMA as recommended, or putting a (long) telescopic whip in.  The TRC-512 radios would be much easier to do an antenna upgrade on.I was also able to find the TRC-512 service manual online. 

Given the significant range increase the antenna upgrade experiments produced I am hopeful that I can bring these radios to the 1/4 or so mile range I want.  I donít want further range for the reasons SIGMA mentioned - super low power means lower probability of intercept (unless the people doing the intercepting are *very* close). 

Iíve thought about grabbing a couple MT1000s or similar Motorola lowband HTs, include the 49 MHz freqs, 6 meter stuff, the 47.420 MHz Red Cross frequency and some others.  Several utility companies in my area use 48 MHz and 49 MHz frequencies (49.580 MHz and below)...and the state Department of Transportation operates an extensive network on 45 MHz/47 MHz, with dozens and dozens of repeaters and lots of simplex use.

Iím sure there are clear frequencies in the 43/44 MHz region but there are several heavy construction contractors using those bands...and Iím not going to use the power companyís lowband frequencies for obvious reasons...

For now Iíll continue to experiment with short range/low probability of intercept purpose stuff on the 49.820 - 49.900 MHz band...49.875 being my primary frequency for now.
« Last Edit: September 29, 2019, 2124 UTC by R4002 »
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Offline Σ

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Re: 49 MHz Range Testing Part 15 Experimentation
« Reply #5 on: September 29, 2019, 2213 UTC »
An old trick that was done in the past was to monitor your "special" unlicensed frequency with PL turned on while you waited for a call. Then when you received a call you'd turn off the receive PL so you can hear all channel activity to make sure you weren't interfering with a legit user. Most older portables had this feature right on the top of the radio.

Actually FCC rules requires you monitor a freq before transmitting to avoid just that. When you picked up a mobile microphone in the old days it would no longer be grounded to the metal car dashboard where your mic hang up clip was mounted. More recently, most land mobile radios had mic hang up clips with a wire attached to sense the mic off hook since vehicle interiors are plastic now.  This would open the receiver so that you no longer had receive PL. This made sure you weren't interfering with a co-channel user. Base stations had a monitor key on the mic that you pressed first to listen to channel activity before calling. This was necessary when many licensees shared one freq but had different PL tones.

I have rarely seen this in the last decade or two. Frequencies are coordinated now and fewer are shared with nearby co-channel users.

The MT1000 can be made into a nice little base station with a vehicular Converta-Com that will bring the antenna out to a UHF connector as well as power the radio off 12 volts. Might be good to have the base station connected to a big antenna to increase its range if needed. Handy if the 49 MHz portables get out of range of each other.
« Last Edit: September 29, 2019, 2231 UTC by Σ »
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Offline Josh

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Re: 49 MHz Range Testing Part 15 Experimentation
« Reply #6 on: September 30, 2019, 2049 UTC »
One way to increase range is to use what HAMs call tiger tails. Simple wires dangling from the bnc or tnc socket under the duck antenna. These wires, in contact with the ground of the rtx would add substantial rx and tx benefit. The ones I have are a 1/4w on 2m, so they'd help on the higher bands too.

In the especialised ops business, some rt guys use a wire or wires trailing ground system attached to their ruck. Ground a wire, or better yet, a multiconductor ribbon cable that dangles from the frame of the ruck to the ground when standing greatly increases tx efficiency when on the move and using the typical flexible tape antenna for hf or higher.

The trailing wire could be fed in series, if a ribbon cable, making for example a 1m long 12 conductor cable 12m long in appearance to the radio. A 68pin (indicating 68 wires) teflon scsi cable of sufficient length would be great for this.
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Offline Σ

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Re: 49 MHz Range Testing Part 15 Experimentation
« Reply #7 on: September 30, 2019, 2215 UTC »
Doing the exact thing for the local ham I am elmering. He is just a little noisy into his favorite repeater with his HT. Next time he is over the house we are attaching a tiger tail to it to see if it improves things a little. The old RS HTX-202/404 HTs had a metal belt clip that would couple to your hand to create the counterpoise. It certainly won't hurt to try it on 49 MHz since it only costs you a piece of wire.
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Offline CoolAM Radio

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Re: 49 MHz Range Testing Part 15 Experimentation
« Reply #8 on: October 01, 2019, 1428 UTC »
I remember around the year 2003 - the 43 Mhz. band was free in Italy & few South American countries





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Offline RobRich

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Re: 49 MHz Range Testing Part 15 Experimentation
« Reply #9 on: October 05, 2019, 0424 UTC »
Add a connector and build a basic wire j-pole. Lots of j-pole plans and calcs on the net. Opt for a BNC if you want to retain handheld use of a rubber duck or similar.

You can use 450-ohm twinlead for the antenna, 50-ohm coax for the feedline, and air-wound coax for a simple choke. Get a slingshot or fishing pole, and raise the antenna via a tree.

Do the same for two units, and you might successfully complete line of sight comms up to several miles assuming enough height and no significant obstructions, even with just milliwatts of radiated power.

I recommend a wire j-pole for being lightweight, easy to build, and readily deployable with a single support. It is also vertically polarized (unless hung sideways ;), which is a plus for talking with other typical handheld users in your expected comms group.

BTW, 49MHz also can do over the horizon even at QRP just like the nearby 6m amateur band, but think more along the lines of using multi-element yagis at decent height on each end of the connection.
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Offline R4002

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Re: 49 MHz Range Testing Part 15 Experimentation
« Reply #10 on: October 05, 2019, 2111 UTC »
Those 43 MHz transceivers are apparently quite popular in Ukraine and Russia and elsewhere.  Used in ways similar to CB/11 meters.  They can be easily modified to do 25 watts output and cover 42.3000 MHz to 45.0875 MHz in 12.5 kHz steps.  Like 11m, its popular with taxis, car services, farmers and the like. 

At some point in the future I'll build a proper quarter wave wire antenna with counterpoise for 49 MHz.  Further scanning of the 49.820-49.900 MHz band has yielded more random FM carriers and open mics on various frequencies.  49.860 MHz, 49.865 MHz, 49.850 MHz, 49.830 MHz are all used in at least one spot near my house/office.  The more I research 49 MHz devices the more I realize the "band plan" is more like guidelines.  Lots of baby monitors use offset channels but also use 20 kHz bandwidth narrow FM - aka "25 kHz" (instead of the usual 11 kHz bandwidth aka "12.5 kHz") - same as lowband land mobile gear.

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Offline R4002

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Re: 49 MHz Range Testing Part 15 Experimentation
« Reply #11 on: October 10, 2019, 1712 UTC »
Well, I went ahead and swapped out one of the rubber duck antennas with a 39 inch telescopic whip antenna from eBay.  Preliminary testing indicates that it hears one of the nearby 49 MHz carriers (a baby monitor/open mic on 49.830 MHz) considerably better than the factory rubber duck.  Seems to double range at which I can receive that signal.  I don't know exactly where the transmitter is located because it can be heard over a relatively large area compared to other 49 MHz carriers I've used as "test beacons".   

For whatever that's worth.  I need to do some more testing with two Maxon PC-50 49 MHz walkie talkies using telescopic whips or one "base station" using an external antenna and another handheld PC-50 49 MHz radio with a telescopic whip since I have a reference test for base station with external antenna and another handheld 49 MHz radio with stock rubber duck antenna. 

I used to have a pair of RadioShack TRC-92 (I believe that was the model) 100mw single-channel CB HTs (100mw input power apparently, so about 50mw output power maybe?) with telescopic whips and crystals for 27.125 MHz aka CB channel 14.  The best range I got out of those was about 1/3 of a mile maybe a little more.  Then the first RadioShack FRS HTs hit the market and even the little entry-level FRS HTs on FRS channel 1 blew the TRC-92s out of the water.  Plus, no telescopic whip to worry about. 

If I can get similar range with these Maxon PC-50s I'll call it a success.  Of course a pair of Motorola MT1000 or HT1000 lowband HTs would work a lot better as far as range goes but I don't want lots of range.  A pair of full-power 40 channel CB handhelds with good antennas and decent VHF HTs (again with good antennas) gives me that range. 

Sometimes more coverage is a bad thing...in an emergency situation where somebody a mile away has a scanner/intercept setup they'll hear you if you're using a Baofeng or FRS or whatever VHF/UHF or CB handhelds to talk to somebody 500 feet away but they probably wouldn't hear you if you're using 49 MHz Part 15 radios.  Low probability of intercept.

I know that 49 MHz has almost no DX possibilities, and as far as Part 15 goes...22m or even 11m might be better options for DX but I also think it has an interesting niche use.  Maybe. 
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Offline Josh

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Re: 49 MHz Range Testing Part 15 Experimentation
« Reply #12 on: October 10, 2019, 1825 UTC »
Honoring a WW2 hero and father of the walkie talkie;
https://www.retrocom.com/Al%20Gross.htm
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Offline Σ

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Re: 49 MHz Range Testing Part 15 Experimentation
« Reply #13 on: October 10, 2019, 2011 UTC »
Quite a few of those low end walkie talkies had regenerative receivers in them and were probably the major factor in limiting the range. Even the ones that had superhets were of low quality. Back in the CB days it wasn't uncommon to hear the walkie talkies better on a mobile CB than they could hear you.

Try adding a few more inches to the telescoping antenna to make it closer to resonant and add a tiger tail counterpoise. Anything that can improve the radiated signal will help especially at those low levels.

There are a lot of the 33 MHz fire radios coming off line now so those are a bargain in disguise. Lots of range on them (I know that's not your goal) but good for lots of things. You can get a land mobile license very easily now.
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Offline R4002

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Re: 49 MHz Range Testing Part 15 Experimentation
« Reply #14 on: October 10, 2019, 2245 UTC »
I have a land mobile license :D (in addition to a ham license and a GMRS license)...it would simply be a question of adding frequencies to the license, which is very simple.  There are plenty of available channels in the 30.580 MHz to 31.980 MHz and 35.020 to 35.980 MHz ranges...plus a few more if you include the 27.430 MHz, 27.450 MHz, 27.470 MHz, 27.490 MHz and 27.510 MHz/27.530 MHz (low power) frequencies and 29.710 MHz, 29.730 MHz, 29.750 MHz, 29.770 MHz and 29.790 MHz land mobile frequencies available for mobile use. 

A lot of the low split radios are on the market (those that cover the 33 MHz fire frequencies) for sure, same with the middle split (36-42 MHz for Motorola gear if I remember correctly), seems like the lower and upper splits (29-37 MHz or thereabouts and 42-50 MHz) are more available on the secondhand market.  Lots of options.

The 39 inch telescopic whip seems to be the way to go.  It was simple enough to do an antenna swap - I'll pull the radios apart again and see about adding a counterpoise. 


Update:

I did some more testing with the telescopic whip equipped Maxon PC-50 (I now have three of them). This time I  used a different known 49 MHz signal (this one on 49.860 MHz / 49.865 MHz - I think itís probably on 49.862 MHz or 49.8625 MHz - my scanner only does 5 kHz steps from 17 MHz to 108 MHz and the Maxon PC-50 is channelized).  Iíll say 49.86 MHz (aka Channel C).

Anyway, simply replacing the rubber duck with the whip seems to increase receive range around 1.5x what it was with the rubber duck.  Itís now the same as the Pro-96 scanner connected to a 1/2 wave VHF high band antenna (not the best antenna setup I know). 

Since I have three PC-50s I will connect one of them to an outdoor wire antenna with counterpoise and then Iíll be able to do a side by side comparison of the telescopic whip and the stock rubber duck as far as receive performance goes.

I remember reading about directional wire antennas for tactical VHF FM use (30-76 MHz), including rhombic and other interesting designs for longer range with your handy PRC-25 or PRC-77 radio.  Itís in the field manual I have around here somewhere. 


Of course, the next logical step aside from secondhand low band gear on 49 MHz is a pair of PRC-77s on 49.850 MHz  8)

As I type that Iím reading about the Alinco DJ-V17L HT - itís a ď50 MHzĒ HT but apparently covers 36 MHz to 59 MHz transmit and receive.
« Last Edit: October 11, 2019, 1445 UTC by R4002 »
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