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The definitive CCR thread... why you won't really save anything.


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#1 gman1971

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Posted 12 December 2019 - 04:34 AM

I'll start the Cheap China Radio (CCR) thread by showing this picture.

 

79677221_2763515633762623_34720853205293

 

That shows the sensitivity of the receiver combined with the channel rejection filtering in dB, which means, any signal value that is above the dBm curve plot will desense the receiver. You can pretty much extrapolate this curve from the last point where it is computed if no advanced filtering is used, like the SLR8000 repeater, with over 120 dB blocking for off frequency stuff, etc.. but unless you have one of those, most mobile radios don't have that kind of additional filtering. So if you live in an are with a noise floor of -50 dBm like I do, pretty much most CCRs will fall apart and desense so bad you won't hear squat. OTOH, radios like the XPR7550e, with super tight front ends, will effortlessly reach over miles when the CCR is deaf as a rock. This also shows why more sensitivity is not better, in fact, more sensitivity with a poor front end filtering means it will desense even faster.

 

IMO, the graph above should be pretty much definitive as to why the pricing is directly proportional to the selectivity + sensitivity on those devices: with the Motorola SLR800 repeater leading the pack at well over 2 grand, the Vertex EVX-5300, new, was around 600 bucks, the TM-V71a, is around 350 bucks new, and well, the GD77 CCR can be purchased new for 65 dollars on eBay. 

 

And here is a very simple procedure to gauge a CCRs performance and if its even worth the expenditure. 

 

1) First off, If no channel selectivity figures are offered, then move on. "These are not the droids you're looking for."

2) Now get the receiver sensitivity figure, usually measured in uV, but with this nice chart you can convert it to dBm at 50 Ohm, link here: http://www.repeater-...vity/dbm2uv.pdf

3) Knowing that any signal above the receiver sensitivity threshold (at any frequency) will desense the receiver you add the selectivity in dB at 25 kHz to the receiver sensitivity in dBm, pay attention to signage, the sensitivity is negative dBm. 

4) Repeat the same for 12.5 kHz. Now, some brands show even narrower kHz dB figures offered. You can add it and find out, but that is usually not as important as the real selectivity for further away signals.

5) As a general rule, any signal received within the receiver frequency range (and in the CCRs even further than that) that is stronger than the 25 kHz selectivity value calculated will desense the receiver.

 

Have at it, and please, correct me if I made any mistakes.

 

G.


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#2 Lscott

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Posted 12 December 2019 - 09:06 AM

I'll start the Cheap China Radio (CCR) thread by showing this picture.

 

79677221_2763515633762623_34720853205293

 

That shows the sensitivity of the receiver combined with the channel rejection filtering in dB, which means, any signal value that is above the dBm curve plot will desense the receiver. You can pretty much extrapolate this curve from the last point where it is computed if no advanced filtering is used, like the SLR8000 repeater, with over 120 dB blocking for off frequency stuff, etc.. but unless you have one of those, most mobile radios don't have that kind of additional filtering. So if you live in an are with a noise floor of -50 dBm like I do, pretty much most CCRs will fall apart and desense so bad you won't hear squat. OTOH, radios like the XPR7550e, with super tight front ends, will effortlessly reach over miles when the CCR is deaf as a rock. This also shows why more sensitivity is not better, in fact, more sensitivity with a poor front end filtering means it will desense even faster.

 

IMO, the graph above should be pretty much definitive as to why the pricing is directly proportional to the selectivity + sensitivity on those devices: with the Motorola SLR800 repeater leading the pack at well over 2 grand, the Vertex EVX-5300, new, was around 600 bucks, the TM-V71a, is around 350 bucks new, and well, the GD77 CCR can be purchased new for 65 dollars on eBay. 

 

And here is a very simple procedure to gauge a CCRs performance and if its even worth the expenditure. 

 

1) First off, If no channel selectivity figures are offered, then move on. "These are not the droids you're looking for."

2) Now get the receiver sensitivity figure, usually measured in uV, but with this nice chart you can convert it to dBm at 50 Ohm, link here: http://www.repeater-...vity/dbm2uv.pdf

3) Knowing that any signal above the receiver sensitivity threshold (at any frequency) will desense the receiver you add the selectivity in dB at 25 kHz to the receiver sensitivity in dBm, pay attention to signage, the sensitivity is negative dBm. 

4) Repeat the same for 12.5 kHz. Now, some brands show even narrower kHz dB figures offered. You can add it and find out, but that is usually not as important as the real selectivity for further away signals.

5) As a general rule, any signal received within the receiver frequency range (and in the CCRs even further than that) that is stronger than the 25 kHz selectivity value calculated will desense the receiver.

 

Have at it, and please, correct me if I made any mistakes.

 

G.

What is the source you got the graphs from and how were the tests done?



#3 WRAF213

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Posted 12 December 2019 - 01:20 PM

Yes, I'd like to see how the tests were done. At best, it's demonstrating adjacent channel selectivity and receiver sensitivity. It's also generalizing all CCRs into the GD-77, which is quite reckless. So, we're trying to point out that these radios are junk, yet trusting the totally-not-copied-and-pasted selectivity measurements the manufacturer provided? Is repeater selectivity measured with cavity filters installed? If your noise floor is -50dBm you should be getting cooked alive.

One odd point to mention is that a dBu to dBm conversion isn't as straightforward as it sounds since a lot of handheld radios (especially CCRs) don't present exactly 50 ohms at the antenna.

I played around with a service monitor and found that my Connect Systems CS-580 had a receiver that was hotter than any of my commercial radios, and it also has a proper 12.5 kHz channel bandwidth for the narrowband setting (which doesn't really matter since I bet you're using it in wideband anyways).

For a well designed receiver, selectivity is a compromise with sensitivity. You can add preselectors and tracking filters, but all of those add insertion loss, which contributes to noise figure. Most CCRs run nearly naked, so the frontend-on-a-chip is exposed behind only a LNA and probably some highpass filters. They can get very sensitive, but this leaves them prone to desense from signals not necessarily near the receiver's frequency. Either way, desense is more complicated than this graph can show.
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#4 gman1971

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Posted 12 December 2019 - 06:22 PM

WRAF, yes the GD77 is probably one of the worst CCRs out there. While Anytone 878 radios fare much better, these still desense easier than the EVX radios I have.

 

LScott, The chart was calculated using the specifications printed on the radio service manuals.

 

For the GD77, the selectivity figures were calculated using a VNA using a similar procedure to the one outlined here.

The sensitivity of the GD77 is claimed by the manufacturer to be -122.dBm

 

The point of this chart was to show at a quick glance why these radios are inferior to things like the SLR8000 repeater from Motorola... I understand desense is a fairly more complex issue, but the chart is easy to read for most people. If you can determine the noise level in you area, that is half of the battle right there.

 

G.



#5 WRAF213

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Posted 12 December 2019 - 06:48 PM

The SLR8000 is a terrible benchmark to use since NOBODY is using that as their primary GMRS radio, particularly as a mobile or portable (nor is it Part 95 type accepted). Repeaters are expected to have excellent desense rejection since they're usually running a 25-40 watt transmitter on the same antenna as the receiver. A lot of the nicer handheld radios have tracking filters on the frontend that gives them stronger desense protection, and you won't find that feature at the CCR price point. You get what you pay for; don't forget the cost of a new commercial radio.


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#6 gman1971

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Posted 12 December 2019 - 09:53 PM

WRAF, I don't think I ever stated, nor implied, that anyone was/should be using the SLR8000 for GMRS. I just pointed the figures to show it on a chart. Whether it is or not part 95 accepted it is hard to argue that the figures on that thing are just amazing, plus it has additional blocking of 110 or 120 dB, so its probably loaded up with filters of all kinds... hence why that is the kind of receiver front end performance one should strive to get, compared to the bottom of the barrel GD77... which is fine for certain things.

 

Yes, thats it right there WRAF: "A lot of the nicer handheld radios have tracking filters on the frontend that gives them stronger desense protection, and you won't find that feature at the CCR price point."

 

I understand that for very advanced guys/gals, like you, the statements I've made are like 1st grade math, but for some of us who trained in other fields, this is the kind of stuff that marketing preys upon to sell CCRs. It would've saved a lot of hassles, time, and ultimately money, should I've have known about what I posted in here. Is it simplified? Yes, but so are Newton's classical mechanics vs the more complete Maxwell's equations... yet we still use Newton's for pretty much anything were v << c... 

 

In the end its someone else's money, they can spend it however they like it. I only wrote this in an effort to help others, who may, or hopefully not, be as clueless as I was when I started buying radio gear.

 

G.

 

 

The SLR8000 is a terrible benchmark to use since NOBODY is using that as their primary GMRS radio, particularly as a mobile or portable (nor is it Part 95 type accepted). Repeaters are expected to have excellent desense rejection since they're usually running a 25-40 watt transmitter on the same antenna as the receiver. A lot of the nicer handheld radios have tracking filters on the frontend that gives them stronger desense protection, and you won't find that feature at the CCR price point. You get what you pay for; don't forget the cost of a new commercial radio.



#7 WRAF213

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Posted 13 December 2019 - 03:14 PM

But it's important to realize when it's not practical to pay for more selectivity. Good commercial handhelds have enough selectivity to allow full-duplex operation by one operator, with a few feet of antenna separation. Good mobiles do better than that. If that's not enough desense protection, there's other issues at play. There's no improvement to be made if there isn't an issue, so it's just wasted money and/or lost functionality.

 

CCRs work just fine as transceivers for 99% of the population. Yes, they don't work in the busy RF environments found at an enthusiast's base station, a command post, or when working near other operators on different in-band channels. They're cheap, show people what the hobby can offer, and include a lot of features (like FPP and ridiculous channel capacity) that new operators need to find their niche within the hobby and understand what parameters need to be configured to operate cleanly on someone else's system. And when they break (probably due to a novice operator blowing out the finals or dropping it), it's not a big investment being lost. They exist in the market for a reason: because they do work, unlike what the topic's title implies. They wouldn't sell if they didn't. It's important to understand their limitations, but they're not as severe as you're making it out to be.


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#8 gman1971

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Posted 13 December 2019 - 05:26 PM

Well, sure, these radios worked much better at our previous house, but since moving to this new house (near the giant antenna) these things aren't cutting it anymore and I never really knew why...  That is why I felt cheated from those radios, once I started to get serious I realized I really threw my money away, as some of those radios I got for 40 dollars are now 9 and no option to ditch them... and then considering the fact that some of the commercial gear available is so cheap, it almost makes no sense to take the bait of the flashy screens, and bells and whistles when these lack in the most important aspect, the RF performance. 

 

I own a ton of CCRs myself, from cheap BF-888S for house intercom to DJ-MD5, GD77s, etc; yes, they work, and these are what got me back into radios... just don't expect much from those once you really want to reach far. 

 

G.

 

 

But it's important to realize when it's not practical to pay for more selectivity. Good commercial handhelds have enough selectivity to allow full-duplex operation by one operator, with a few feet of antenna separation. Good mobiles do better than that. If that's not enough desense protection, there's other issues at play. There's no improvement to be made if there isn't an issue, so it's just wasted money and/or lost functionality.

 

CCRs work just fine as transceivers for 99% of the population. Yes, they don't work in the busy RF environments found at an enthusiast's base station, a command post, or when working near other operators on different in-band channels. They're cheap, show people what the hobby can offer, and include a lot of features (like FPP and ridiculous channel capacity) that new operators need to find their niche within the hobby and understand what parameters need to be configured to operate cleanly on someone else's system. And when they break (probably due to a novice operator blowing out the finals or dropping it), it's not a big investment being lost. They exist in the market for a reason: because they do work, unlike what the topic's title implies. They wouldn't sell if they didn't. It's important to understand their limitations, but they're not as severe as you're making it out to be.



#9 RCM

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Posted 14 December 2019 - 12:16 AM

Well, sure, these radios worked much better at our previous house, but since moving to this new house (near the giant antenna) these things aren't cutting it anymore and I never really knew why...  That is why I felt cheated from those radios, once I started to get serious I realized I really threw my money away, as some of those radios I got for 40 dollars are now 9 and no option to ditch them... and then considering the fact that some of the commercial gear available is so cheap, it almost makes no sense to take the bait of the flashy screens, and bells and whistles when these lack in the most important aspect, the RF performance. 

 

I own a ton of CCRs myself, from cheap BF-888S for house intercom to DJ-MD5, GD77s, etc; yes, they work, and these are what got me back into radios... just don't expect much from those once you really want to reach far. 

 

G.

You need to take on ECRs next: Expensive Chinese Radios. Still made in China, but repackaged with an American name and a price tag to rival that of a new Icom.

I think everybody here knows what radio I'm talking about.


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#10 gman1971

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Posted 14 December 2019 - 12:54 AM

My EVX-5300 radios are made in China and branded as Vertex Standard, I know these don't desense as bad as the CCRs do... so its just the C. part of the acronym what I think there should be some awareness. The Vertex Standard radios made in Japan seem, in paper at least, a lot better than the ones made in China.

 

I haven't tinkered with Hytera radios and probably never will...  

 

Motorola radios AFAIK are made in Malaysia, not really China, but yeah... I understand the point.

 

G.



#11 RCM

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Posted 14 December 2019 - 10:04 AM

My EVX-5300 radios are made in China and branded as Vertex Standard, I know these don't desense as bad as the CCRs do... so its just the C. part of the acronym what I think there should be some awareness. The Vertex Standard radios made in Japan seem, in paper at least, a lot better than the ones made in China.

 

I haven't tinkered with Hytera radios and probably never will...  

 

Motorola radios AFAIK are made in Malaysia, not really China, but yeah... I understand the point.

 

G.

Nope, I don't think you do. I was talking about Midland.


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#12 gman1971

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Posted 14 December 2019 - 02:57 PM

I had no idea Midland was made in China... so if that is the case then perhaps it falls in the EVX category? Designed in another country and built in China? Or are Midland radios just rebadged TYT stuff? 

 

G.

 

Nope, I don't think you do. I was talking about Midland.



#13 RCM

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Posted 14 December 2019 - 05:07 PM

I had no idea Midland was made in China... so if that is the case then perhaps it falls in the EVX category? Designed in another country and built in China? Or are Midland radios just rebadged TYT stuff? 

 

G.

They're just reflashed and rebadged Chinese stuff. A member who hasn't been around for awhile, Hans, posted exactly what they are awhile back.


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#14 gman1971

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Posted 15 December 2019 - 01:35 AM

That is most unfortunate to hear, so therefore these should also be added in the CCR category and avoided as well. I think Motorola (Vertex Standard), Icom and Kenwood are probably the only few brands I would consider at this point. In the end, buying a nice EVX-539 with dotmatrix display UHF G7 model will save you a lot of trouble in the long run, plus those radios are pretty well built and will survive pretty much anything you throw at them.

 

But that is just me.

 

G.

 

They're just reflashed and rebadged Chinese stuff. A member who hasn't been around for awhile, Hans, posted exactly what they are awhile back.



#15 Downs

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Posted 17 December 2019 - 10:01 AM

They're just reflashed and rebadged Chinese stuff. A member who hasn't been around for awhile, Hans, posted exactly what they are awhile back.

This is certainly the case on their dual band HAM radio. Their DBR2500 is a rebadged AT778 from Anytone.

Rugged Radios is infamous for this rebading. Selling UV5Rs with their tag on it for 80 dollars. Their 60 watt vhf radio they sell for 400 dollars is a rebadged 130 dollar TYT TH9000D.

Sent from my SM-G892A using Tapatalk
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A pile of "cheap Chinese radios", BF888s, UV5Rs, UV82s, KGUV8Ds, BFF8HP, UV50X2, and a few "good" radios, Yeasu FT310 (airband/nav), Yeasu FT90R (no longer in mobile service used as a base radio)


#16 gman1971

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Posted 17 December 2019 - 10:42 AM

Anytone, some of their latest stuff is certainly better, but TYT (and their clones), in my experience, they are the worst of the CCRs, even crappier than the UV5R, their front ends lacks of any filtering and just desenses.

 

G.



#17 RCM

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Posted 17 December 2019 - 07:09 PM

This is certainly the case on their dual band HAM radio. Their DBR2500 is a rebadged AT778 from Anytone.

Rugged Radios is infamous for this rebading. Selling UV5Rs with their tag on it for 80 dollars. Their 60 watt vhf radio they sell for 400 dollars is a rebadged 130 dollar TYT TH9000D.

Sent from my SM-G892A using Tapatalk

Rugged Radios also misleads people to believe that as their customer, they can legally transmit on business band itinerant frequencies under RR's license. It's not a 100 percent lie*, but it is a gross misrepresentation.

 

* A customer can do that at certain events where Rugged Radios is physically present and gives the customer express permission to transmit on the specific frequencies in use, but only at the event location and while the event is going on.


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#18 Downs

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Posted 17 December 2019 - 09:39 PM

They have a ton of business band frequencies that arent even theirs on there. And unless you corner them they try to skirt answering any questions about licensing.

Theyre a shady underhanded company but they have a good marketing team and sponsor the crap out of the off road and racing community.

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A pile of "cheap Chinese radios", BF888s, UV5Rs, UV82s, KGUV8Ds, BFF8HP, UV50X2, and a few "good" radios, Yeasu FT310 (airband/nav), Yeasu FT90R (no longer in mobile service used as a base radio)


#19 gman1971

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Posted 17 December 2019 - 10:00 PM

That is a new level of misrepresentation.... who knew...

 

Rugged Radios also misleads people to believe that as their customer, they can legally transmit on business band itinerant frequencies under RR's license. It's not a 100 percent lie*, but it is a gross misrepresentation.

 

* A customer can do that at certain events where Rugged Radios is physically present and gives the customer express permission to transmit on the specific frequencies in use, but only at the event location and while the event is going on.


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#20 Ian

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Posted 05 January 2020 - 11:41 PM

But it's important to realize when it's not practical to pay for more selectivity. Good commercial handhelds have enough selectivity to allow full-duplex operation by one operator, with a few feet of antenna separation. Good mobiles do better than that. If that's not enough desense protection, there's other issues at play. There's no improvement to be made if there isn't an issue, so it's just wasted money and/or lost functionality.

 

CCRs work just fine as transceivers for 99% of the population. Yes, they don't work in the busy RF environments found at an enthusiast's base station, a command post, or when working near other operators on different in-band channels. They're cheap, show people what the hobby can offer, and include a lot of features (like FPP and ridiculous channel capacity) that new operators need to find their niche within the hobby and understand what parameters need to be configured to operate cleanly on someone else's system. And when they break (probably due to a novice operator blowing out the finals or dropping it), it's not a big investment being lost. They exist in the market for a reason: because they do work, unlike what the topic's title implies. They wouldn't sell if they didn't. It's important to understand their limitations, but they're not as severe as you're making it out to be.

 

Believe it or not, the GD-77S is my favorite radio at the moment.  It solves practical problems by slinging squiggles, and it's even type-accepted as a business radio (No FPP).  As such, it qualifies as the "surplus commercial equipment" that the 2017 memorandum stated was never intended to be banished from the GMRS, and I believe it's legal under the latest regulations.

 

And at five watts, it's my most powerful cheap squiggle-slinger.  Used with Motorola gear (2W) on both high and low (1W), it's absolutely comprehensible in two directions when cell phones aren't getting enough signal to send a text message.

 

Is it "good"?  Apparently not.  Is it good enough?  For me and those like me, yeah it is.  (And if it gets dropped, I didn't just break irreplaceable hardware!)

 

Edited to add:  And at 5w back and forth, it'll reach from handie to handie all the way to our grocery store, and inside too.  As far as I'm concerned, that performance is mind-blowing.






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