Jump to content
Sign in to follow this  
headhunter23

curious about frs radio's, can they be modded?

Recommended Posts

Was reading up some of mr-cam's fcc stuff and one of the articles was talking about family radio service for hunting. Anyways probably completely off base and probably not possible, but curious as to wether these frs radio's can be modded to another frequency and merged with radio and airplane receiver. I don't know too much about that kind of stuff but figured if there's already the 20 mile range of these things, wondering if they can be adapted at all.

Ivan.

Share this post


Link to post
Share on other sites

There's a guy over at rcgroups that flies with a hacked FRS (or something similar). I recall his range is extraordinary. Keep in mind that the FRS band's FCC regulations forbid such things, so it's not a hack for those that want to operate within the rules. Modifying them to operate on regular R/C frequencies would probably net a system that is no better than a typical R/C system.

Share this post


Link to post
Share on other sites

Coils and capacitors would need to be changed to match the new tuning range. Just changing a few crystals won't cut it. If you were a Ham, you could re-crystal and retune the the 49mhz FRS radios to the 6 meter (50mhz) band without too much trouble, 'Course you'd still need more equipment that a multimeter.

Share this post


Link to post
Share on other sites

In the USA, an FRS radio operates in the UHF band (~450Mhz) and has a RF power limit of 500mW. A R/C system operates in the VHF band (72-75Mhz) and has a limit of 750mW. My gut feeling is that a high quality R/C receiver would have better sensitivity (or be at least as good as a FRS). So, a FRS system converted to R/C use would just not seem to be something that would work much better than a stock R/C system of reasonable quality.

Hence my comment: "Modifying them to operate on regular R/C frequencies would probably net a system that is no better than a typical R/C system."

For sure, the conversion from a UHF system to VHF would not be simple at all. But, don't let me stop you.

Share this post


Link to post
Share on other sites

I had thought there was an FRS band at 49 mc where they sell some of the hand held radios although I didn't (still don't) know what service it was/is, but apparently not. Just never paid that much attention to it.

I do agree with your gut feeling that a 72 mc radio would have better sensitivity than a 450 unit as it's easier to attain a narrower bandwidth in the front end of a 72mc unit than a 450mc receiver. I have no plans to do it but could use a converter from 450 to 72mc for greater sensitivity at 450. Maybe that's what the guy at RCG did... Haven't seen the thread.

One nice thing about playing with the receiving end is anyone can experiment.

Edited by W3FJW-Ron

Share this post


Link to post
Share on other sites

Hmmmm... still trying to understand, your saying that frs radios are less sensitive but seem to have more range than a good radio system(say store bought futaba 72mhz is what I would call a reasonably good system, seems to get around 2-2.5km)? Just trying to associate. as it still doesn't make sense... again I'm not too technical in this respect. Have reread a couple times... so there seems to be less power for frs radio system correct? Are you saying that the data just wouldn't be consistent enough to fly?

MMm...... ok... try rewording. By converting from 450mhz to 72mhz you loose the 28 miles(furthest distance found,45km) to a 4 miles? Or are you saying the 72mhz does have a greater range of 28 miles, I guess if everything was perfect or custom?

Sorry for questions, just trying to understand. ;)

Edited by headhunter23

Share this post


Link to post
Share on other sites
By converting from 450mhz to 72mhz you loose the 28 miles(furthest distance found,45km) to a 4 miles?

So, where are you getting the information on 28 mile range for FRS? Typical range is about 1 mile in decent LOS environments. A good R/C system should do much further than that.

Perhaps you mean GMRS? GMRS is allowed 50 watts and in ideal environments can reach 20 miles or more.

I had thought there was an FRS band at 49 mc where they sell some of the hand held radios

Those 49Mhz Walkie-Talkies are not part of the FRS band. They are just more modern equivalents of the low cost 27Mhz stuff that was popular over three decades ago.

Share this post


Link to post
Share on other sites

#1, I don't know where you got the idea that FRS radios have a range of 20 miles. Must be that advertising hype..

I doubt that under the same conditions, time of day or night, humidity, etc., that the 450 mhz signal will be any better, and probably worse, than the 72mhz radios. FRS radios are permitted half a watt, and I don't know whether that is input power or output power. If input, then the best output power would be about half or slightly better or around 250mw. A typical RC Tx at 72mhz is rated at one tenth watt or 100mw of power with about the same efficiency. It requires more power at FRS frequencies to equal the range of our 72mhz equipment

The VHF band has much different signal propagation and absorption properties than the UHF band. A 72mhz system, all things being equal under typical conditions will have a greater range than a 450 (UHF) unit because path loss and signal attenuation due to humidity, smog, and a hundred other things having a greater effect upon the latter.

We are talking about line of sight so in actual practice 72 will have a greater range than 450 due to less path loss.

A 72mhz signal under the right atmospheric conditions can travel around the world, and a 450mhz signal under the right conditions can be bounced off the moon. VHF frequencies and all above depend mostly upon line of sight with no buildings, hills or trees in between.

Rx sensitivity plays a big roll as well. It's easier and cheaper to obtain a narrower front end (RF stages) bandwidth giving greater sensitivity at 72mhz than at 450. If you're really interested in learning more about this I'd suggest Googling RF Signals, RF Bandwidth or RF propagation.

Edited by W3FJW-Ron

Share this post


Link to post
Share on other sites

http://www.cobra.ca/cobra/en/product/printer/PHWC594 was where I first noticed 45km range, wikipedia states under optimum(which is possible with rc airplanes as it would be line o sight above sky) 40 miles or 60km has been possible. http://en.wikipedia.org/wiki/Family_Radio_...cal_information

rc-cam your right about the gmrs, whole thing is slightly confusing. Seems that if your frs radio has gmrs then the watts can increase to 2 watts in canada eh!? What's that all a boot? Eh? Anyways kidding aside, from what I've been reading is that gmrs has a few channels devoted to frs. About gmrs, are there repeaters involved? Or are the radios able to transimit that far merely by the increase in watts?

Now if it's just by the watts increase, modding the radios(with gmrs) to something that can be used for rc airplanes, then my understanding is the wattage would be above and beyond the allowed wattage(the .750watts?) Which my understanding would either be illegal or require a license at those levels.

But just for theory sake, would it work if you modded these new frs radios?

Share this post


Link to post
Share on other sites
http://www.cobra.ca/cobra/en/product/printer/PHWC594 was where I first noticed 45km range,

Honestly, if model R/C equipment manufacturers used the same assumptions in making range claims, they would be touting 50+ mile range. Furthermore, using the similar exaggerated assumptions, a VHF communication system with similar RF power could reach several hundred miles under ideal skip conditions.

BTW, I found a person's review of that radio. His range was:

House To Car: 1.43 miles

House to person: 1.83 miles

Person to person: 2.19 Miles

Car to car: 1.23 miles

There is nothing special about a FRS or GMRS system that would make it a better electronic solution for R/C control. Practically speaking, it could be worse since in the general public, you'll find more of these personal communications systems in use than R/C transmitters, so the airwave conflicts will be higher. And technically speaking, the higher operating frequency means the RF path loss will be much higher, hence shorter range.

Now if it's just by the watts increase, modding the radios(with gmrs) to something that can be used for rc airplanes, then my understanding is the wattage would be above and beyond the allowed wattage(the .750watts?) Which my understanding would either be illegal or require a license at those levels. But just for theory sake, would it work if you modded these new frs radios?

With all else equal, it would take a 30 watt UHF/GMRS transmitter to have the same effective range as a 0.75W VHF/72 Mhz communication system. That is because RF path loss is frequency dependent.

If all you are interested in is more RF power, then that can be done to a 72Mhz R/C transmitter. It is just as illegal as hacking a GMRS or FRS radio for other purposes such as R/C control. So if you are looking for something that is license-free that works within the FCC rules, then neither solution is feasible.

Share this post


Link to post
Share on other sites

hmmm... just an idea is all, was curious as to wether it had been done and wether it actually worked. Buggar. claiming that much distance and only getting a mile or two is more than false advertising. Although I'm pretty sure we got over 2km on the water with our frs's 8-10 years ago, I would have thought the range would have increased by then atleast based on all the companys advertising such. But I'm sure water and being up north with not much interference helped a lot in that aspect.

Ivan.

Share this post


Link to post
Share on other sites

Keep in mind headhunter, that 2km is just over a mile. And being on the water (assuming no tall waves) is line of sight. Efficiency of RF devices may have increased in modern equipment, but the laws of physics and path loss remain the same.

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
Sign in to follow this  

×