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

[gman1971]

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

 

 

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-builder.com/tech-info/measuring-sensitivity/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.

[gman1971]

When I first entered the DMR portion of ham radio, I got a good deal on a really well cared for XPR7550 (UHF). I had a custom leather holster made for it, along with the D-Ring for my belt. While it looks nice it is quite heavy, at least compared with my current favorite the AT-878 which weighs just over half as much, is about half the size, and has three times the features as the XPR7550.

 

The first time I carried to Dayton for the Hamvention, I found to my dismay that while I had packed a half-dozen HTs along on the trip (why I have no idea!), I had forgotten the charger for the XPR7550!

 

Fortunately, one of my DMR friends had an Impress charger and hand mic at his booth, so I bought both and all was well again. Now I find myself not even having turned on the XPR7550 for nearly two years. I have the software and programming cable, two chargers, two batteries, the leather holster and speaker mic and need to find a good home for this package. I do keep the batteries rotated and freshly charged though.

 

Now I've found that the battery on my GD-77 has gone bad. It won't hold a charge at all. Thirty seconds fresh off the charger and the radio loses power. I'm not sure about replacing the battery. I may just toss the radio in the trash.

 

I need to sell my MD-2017 and Ailunce HD-1 if possible. I just don't need that many HTs cluttering up the house.

 

It's too bad the AT-578 doesn't have a separation kit, as I'd really like that in my mobile. Running in in 220/440 DMR crossband would be nice. At least then I'd get some use out of my 220 HT that otherwise just sits around feeling lonely. I'm blessed with having a very wide-area 220 repeater here in NW Indiana, but no one else either uses it or has a radio...

 

Most of my old CCR radios are just dead weight too, cluttering around the house. I guess I could sell a pack of 10 BF-888s for 40 bucks or so haha... most of my FM only portables aren't worth much anymore, I guess I could sell them by weight? hahaha.

 

The MD-2017 and the HD-1 have pretty poor front ends, they desense faster than you can say hello. I guess its like the features of the 878 except with terrible RF performance... the 878 is a far better radio IMO. I am considering picking one to replace my MD5 b/c I can get one with Bluetooth... lets just say I am spoiled with Senna helmet mounted intercom talking over with the 578 with the press of a remote PTT button... just amazing, no need to grab the microphone... nope.

 

Crossband DMR preserves the input ID, this information is not available anywhere; which means, when operating crossband mode its not the DMR ID of the 578 radio what the receiver sees, but the DMR ID of the radio that is being "crossbanded"

 

G.

[kipandlee]

Most of my old CCR radios are just dead weight too, cluttering around the house. I guess I could sell a pack of 10 BF-888s for 40 bucks or so haha..

after i'm done playing with the CCR radios i program a few freq  and give them to the grandkids and nieces and nephews they don't last long after that but the kids have fun while they do 

[gman1971]

No grandkids here yet... just kids...  

 

G.

[Ian]

Look, I know it’s an objectively bad radio, but it sat at the intersection of a Venn diagram that makes it uniquely compelling to me. Grocery store’s about five miles, and all I’ve known up to this point is bubblepack junk, a couple very nice Radio Shack FRS units, sadly underused, and now with PTT keys gone crunchy and disintegrated disabling otherwise sweet hardware, and Motorola Spirit SV-22 MURS units. Those are my favorite, but they’re heavy and can barely make it to the gas station, because VHF.

 

I’m not saying that they’re good at receive desnsing, but if you want bad bad, you should look at the Retevis RT-22 and its clones. I’ve never gotten the GD-77 to desense, but those do it at the drop of a hat.

 

I’m not hugely demanding of simplex comms. If I could find decent FRS, I’d be happy with that… except I have, in the form of the Motorola Sport 7. At this age, only about half of the ones on eBay work, and I’ve bought every one available, and I have two. They’re fantastic. Those Radio Shack ones are smaller, but they use AAAs (though they’ll charge them if you have a 9v adapter) and lack CTCSS, but can be set to any one of 22 channels with the DIP switches, whereas the Motorolas can only do seven channels, (1, 4, 8, 11…) and seven codes chosen more or less at random (set with a dial designed to be wrenched on with a quarter behind the battery compartment).

 

As for the GD-77, I’ve bowed to interoperability and run it narrowbanded, since most of my fleet is narrowband-only, and only the Talkabout Distances do wideband.

 

Ultimately, the project for which it was bought was to figure out who the heck was running DMR on channel 16 at the local park. Sadly, either the traffic’s encrypted, or setting up DMR is simply beyond me (for now…).

 

Still, if I’m carrying only one radio, there’s a good chance that’s the one. After I lost one of my Anytones to a drop, I’m leery about carrying irreplaceable hardware into the field (even if it’s just Home Depot) without careful consideration. Commercial-grade Motos (into which I place even the Sport 7) are reassuring, as is “not irreplaceable”. I have a wealth of good radios to pick from as my needs evolve, and I thank you for your advice on them.

 

CCRs have their place… which is “close to whoever you need to talk to.”

[gman1971]

Well, I am sorry if I call BS to the 5 miles on narrowband, portable to portable using GD-77s. I am lucky if I get more than 1 mile using my GD-77 on UHF, and going inside a store, or any building for that matter, the range halves. Even with my base antenna on a Vertex Standard EVX-5300 running just 10W, the GD-77 is deaf hearing the base beyond 2-3 miles while the EVX-5300 can ANY 5W portable at over 11 miles away...  that tells you the receiver on those is just garbage. In contrast, the Alinco DJ-MD5 can hear the base at 3 miles pretty much full quiet, the GD77 cannot.

 

Motorola, even their FRS stuff is hardly a CCR, and I also have a few old bubblepack radios that destroy the GD77 in every aspect (except price)... the first one that comes to my mind is the Midland G11 with removable antenna, which was a pretty nice radio, I still have a few of those lying around, got pretty decent range out of those, the antennas were very well tuned too...

 

I understand as I've recently lost my Alinco DJ-MD5, it wasn't a Motorola pricetag kind of loss, but it still sucked. I will get another one at some point b/c I like those MD5 radios b/c they are small and have dual band so I can listen to all DMR traffic around town.

 

My experience with MURS has been the opposite, VHF reaches WAY further than UHF for the same amount of power.

 

G.

 

Look, I know it’s an objectively bad radio, but it sat at the intersection of a Venn diagram that makes it uniquely compelling to me. Grocery store’s about five miles, and all I’ve known up to this point is bubblepack junk, a couple very nice Radio Shack FRS units, sadly underused, and now with PTT keys gone crunchy and disintegrated disabling otherwise sweet hardware, and Motorola Spirit SV-22 MURS units. Those are my favorite, but they’re heavy and can barely make it to the gas station, because VHF.

I’m not saying that they’re good at receive desnsing, but if you want bad bad, you should look at the Retevis RT-22 and its clones. I’ve never gotten the GD-77 to desense, but those do it at the drop of a hat.

I’m not hugely demanding of simplex comms. If I could find decent FRS, I’d be happy with that… except I have, in the form of the Motorola Sport 7. At this age, only about half of the ones on eBay work, and I’ve bought every one available, and I have two. They’re fantastic. Those Radio Shack ones are smaller, but they use AAAs (though they’ll charge them if you have a 9v adapter) and lack CTCSS, but can be set to any one of 22 channels with the DIP switches, whereas the Motorolas can only do seven channels, (1, 4, 8, 11…) and seven codes chosen more or less at random (set with a dial designed to be wrenched on with a quarter behind the battery compartment).

As for the GD-77, I’ve bowed to interoperability and run it narrowbanded, since most of my fleet is narrowband-only, and only the Talkabout Distances do wideband.

Ultimately, the project for which it was bought was to figure out who the heck was running DMR on channel 16 at the local park. Sadly, either the traffic’s encrypted, or setting up DMR is simply beyond me (for now…).

Still, if I’m carrying only one radio, there’s a good chance that’s the one. After I lost one of my Anytones to a drop, I’m leery about carrying irreplaceable hardware into the field (even if it’s just Home Depot) without careful consideration. Commercial-grade Motos (into which I place even the Sport 7) are reassuring, as is “not irreplaceable”. I have a wealth of good radios to pick from as my needs evolve, and I thank you for your advice on them.

CCRs have their place… which is “close to whoever you need to talk to.”

[Elkhunter521]

Gosh,

Doesn't anybody have an opinion here.

[DeoVindice]

Gosh,

Doesn't anybody have an opinion here.

You know what they say about opinions...

 

...we all know that Kenwood is the only way (unless you've mastered /\/\ software)

[berkinet]

...Those are my favorite, but they’re heavy and can barely make it to the gas station, because VHF....

...CCRs have their place… which is “close to whoever you need to talk to.”

 

Well, I can't say I agree on your first point (see below), but, I do agree whole-heartedly with your conclusion.

 

...My experience with MURS has been the opposite, VHF reaches WAY further than UHF for the same amount of power.

 

Agreed. In open space, VHF will travel further, have lower path loss  and better building penetration than UHF (See this paper for more information). On the other hand, UHF may actually work better inside a building because of signal splatter and reflection.

[gman1971]

"It is the way", that sounds like the Mandalorian, man. hahaha.

 

I have some Kenwoods lying around, but I use Vertex Standard as my primary base/mobile rigs, the software is easy to work with and its free... /\/\ would be nice to have... and none of those are CCR...  

 

G.

 

 

You know what they say about opinions...

...we all know that Kenwood is the only way (unless you've mastered /\/\ software)

[WRAF213]

I’m not saying that they’re good at receive desnsing, but if you want bad bad, you should look at the Retevis RT-22 and its clones. I’ve never gotten the GD-77 to desense, but those do it at the drop of a hat.

 

Look at how little filtering the RT-22 has. There's all sorts of unpopulated pads on the production model that aren't on the FCC submitted model. I bet those harmonics aren't 50dB down on production models.

 

 

Also, my primary GMRS long range link is all done using Vertex Standard commercial gear. As I've quickly (and expensively) realized, sticking anything UHF non-commercial grade to the Diamond X50C2 (a 7.2 dBd UHF gain vertical antenna) immediately blanked out, desensed, the receiver due to the massive RFI coming from the 1400-foot Candelabra tower that is less than 2 miles from my house...

Again, you're in a highly unconventional RF environment, RF power coming from the Candelabra transmitters through a typical UHF passband (370-530 MHz) should be in the ballpark of 0dBm. Most people are around -50dBm. That's a HUGE difference.

 

That said, CCRs aren't meant to be used on fixed antennas; they're designed to be used as portable radios. Most handhelds will show measurable desense on a high-gain base antenna, CCR or not. The typical CCR construction with a wide-open frontend happens to have a lot more desense. In open spaces away from other transmitters, they have a slight advantage due to less filtering loss.

 

They have their place, and that's on-site business use on the hip; can't desense if the strongest transmitter is the repeater you're using. They also work good enough for amateur use that people keep buying them. Few people in reality will cite receive performance as a reason to upgrade from a D878UV or something to a Motorola or Kenwood, it's mostly for audio quality.

 

 

My experience with MURS has been the opposite, VHF reaches WAY further than UHF for the same amount of power.

Over here, where the noise floor is high on VHF, I get better coverage on GMRS than MURS, and better 800 MHz Part 90 reception than 460 MHz Part 90 reception. In my experiences with line-of-sight conditions, the higher gain from UHF antennas gives better audio (helps to make up for deep fades, which are briefer on UHF), while in mobile-to-mobile situations with some separation VHF has an advantage in punching through terrain. UHF has much better spot coverage. For mobile-to-mobile operation, ~50W out into a gain antenna on GMRS should give universally better coverage than your Part 95 compliant MURS setup. Portable-to-portable simplex will be much more variable due to terrain. Noise floor is also an important consideration in urban environments, and lower frequencies will have more noise than higher frequencies.

[gman1971]

Read the article, thank you!

 

G.

 

Well, I can't say I agree on your first point (see below), but, I do agree whole-heartedly with your conclusion.

 

 

Agreed. In open space, VHF will travel further, have lower path loss  and better building penetration than UHF (See this paper for more information). On the other hand, UHF may actually work better inside a building because of signal splatter and reflection.

[gman1971]

I have a ton of them, for intercom, so yep, I use them for that... again, but for long range I use commercial grade gear.

 

Well, the two TH-F6a I have don't seem to desense too bad on the same antenna where the GD77 won't hear anything. In fact, the TH-F6a seems to desense less than the TM-V71a on that same antenna, as it picks AM airband from the Madison ATIS tower much better and clearer than the TM-V71a (actually than the two TM-V71a I have) So, there is something to be said about Kenwood being very nice radios.

 

With that said, the EVX-5300 seems to be a much better radio than either the TH-F6a and the TM-V71a in terms of receiver on MURS, as in WAAY better, while it has lower advertised sensitivity, it filters the junk surprisingly well and it picks the portables clearer than the Kenwoods do.

 

Yes, that big tower doesn't help my situation...  hopefully in a couple of years I can move to a higher location, ideally 10+ miles away from the flamethrower antenna...

 

G.

 

 

Look at how little filtering the RT-22 has. There's all sorts of unpopulated pads on the production model that aren't on the FCC submitted model. I bet those harmonics aren't 50dB down on production models.

 

 

Again, you're in a highly unconventional RF environment, RF power coming from the Candelabra transmitters through a typical UHF passband (370-530 MHz) should be in the ballpark of 0dBm. Most people are around -50dBm. That's a HUGE difference.

 

That said, CCRs aren't meant to be used on fixed antennas; they're designed to be used as portable radios. Most handhelds will show measurable desense on a high-gain base antenna, CCR or not. The typical CCR construction with a wide-open frontend happens to have a lot more desense. In open spaces away from other transmitters, they have a slight advantage due to less filtering loss.

 

They have their place, and that's on-site business use on the hip; can't desense if the strongest transmitter is the repeater you're using. They also work good enough for amateur use that people keep buying them. Few people in reality will cite receive performance as a reason to upgrade from a D878UV or something to a Motorola or Kenwood, it's mostly for audio quality.

 

 

Over here, where the noise floor is high on VHF, I get better coverage on GMRS than MURS, and better 800 MHz Part 90 reception than 460 MHz Part 90 reception. In my experiences with line-of-sight conditions, the higher gain from UHF antennas gives better audio (helps to make up for deep fades, which are briefer on UHF), while in mobile-to-mobile situations with some separation VHF has an advantage in punching through terrain. UHF has much better spot coverage. For mobile-to-mobile operation, ~50W out into a gain antenna on GMRS should give universally better coverage than your Part 95 compliant MURS setup. Portable-to-portable simplex will be much more variable due to terrain. Noise floor is also an important consideration in urban environments, and lower frequencies will have more noise than higher frequencies.

[Ian]

Well, I can't say I agree on your first point (see below), but, I do agree whole-heartedly with your conclusion.

 

 

Agreed. In open space, VHF will travel further, have lower path loss  and better building penetration than UHF (See this paper for more information). On the other hand, UHF may actually work better inside a building because of signal splatter and reflection.

Super cool, thanks!

 

 

Well, I am sorry if I call BS to the 5 miles on narrowband, portable to portable using GD-77s. I am lucky if I get more than 1 mile using my GD-77 on UHF, and going inside a store, or any building for that matter, the range halves. Even with my base antenna on a Vertex Standard EVX-5300 running just 10W, the GD-77 is deaf hearing the base beyond 2-3 miles while the EVX-5300 can ANY 5W portable at over 11 miles away...  that tells you the receiver on those is just garbage. In contrast, the Alinco DJ-MD5 can hear the base at 3 miles pretty much full quiet, the GD77 cannot.

 

Motorola, even their FRS stuff is hardly a CCR, and I also have a few old bubblepack radios that destroy the GD77 in every aspect (except price)... the first one that comes to my mind is the Midland G11 with removable antenna, which was a pretty nice radio, I still have a few of those lying around, got pretty decent range out of those, the antennas were very well tuned too...

 

I understand as I've recently lost my Alinco DJ-MD5, it wasn't a Motorola pricetag kind of loss, but it still sucked. I will get another one at some point b/c I like those MD5 radios b/c they are small and have dual band so I can listen to all DMR traffic around town.

 

My experience with MURS has been the opposite, VHF reaches WAY further than UHF for the same amount of power.

 

G.

 

Actually, only one GD-77s.  The other is either a Midland MXT275, or an Anytone TERMN-8R.  Perhaps they're covering up for the weakness of the GD-77s' front-end filtering with clean output into a low-noise area?  I know I don't have any repeaters nearby, the only thing I can hear from here is, occasionally from a hilltop, a Jacksonville repeater automatically ID'ing, so I suspect I'm in an unexpectedly favorable RF environment.  Terrain is Florida, so flat as a pancake.  I have a few repeaters handy when I go to the beach, but the middle of the state is a dead zone.  Also, I'm the only one who ever uses those repeaters in Cocoa Beach, as far as I can tell; I like to monitor them and SARnet when I'm beaching it up.

 

This place is just a dead zone, for the most part.  Every third time I drive by a park, I hear DMR on channel 16.  Occasionally a kid with a walkie-talkie after Christmases.  But for all I scan, I don't hear much at all. 

 

Edit:  Nah, you were right.  I just checked the maps, and it's closer to 1.7 miles to the grocery store.

[gman1971]

Well, 1.7 miles seems feasible considering only one GD77 is used, and being in Florida with a low RFI environment helps too. The Anytone and the Midland probably have a much better front end than the GD-77S too, which is as bad as they come, worse than the UV-5R/GT-3 radio

 

G.

 

 

Super cool, thanks!

 

 

 

Actually, only one GD-77s.  The other is either a Midland MXT275, or an Anytone TERMN-8R.  Perhaps they're covering up for the weakness of the GD-77s' front-end filtering with clean output into a low-noise area?  I know I don't have any repeaters nearby, the only thing I can hear from here is, occasionally from a hilltop, a Jacksonville repeater automatically ID'ing, so I suspect I'm in an unexpectedly favorable RF environment.  Terrain is Florida, so flat as a pancake.  I have a few repeaters handy when I go to the beach, but the middle of the state is a dead zone.  Also, I'm the only one who ever uses those repeaters in Cocoa Beach, as far as I can tell; I like to monitor them and SARnet when I'm beaching it up.

 

This place is just a dead zone, for the most part.  Every third time I drive by a park, I hear DMR on channel 16.  Occasionally a kid with a walkie-talkie after Christmases.  But for all I scan, I don't hear much at all. 

 

Edit:  Nah, you were right.  I just checked the maps, and it's closer to 1.7 miles to the grocery store.

[JLeikhim]

Many years back, before these CCR became the rage, it was a common complaint of ham users of Japanese handhelds that when replacing the factory supplied "rubber duckie" antenna with a 5/8 wave dipole or a base station antenna that the receiver sensitivity would erode. 

 

This was quickly identified as being a combination of both poor RF front end selectivity and poor dynamic range and IMD .

 

It would be interesting to subject these CCR radios as well as known good commercial grade radios to the rigorous testing of TIA603D.

 

Lacking the complete facilities to do so, it occurred to me that a UHF TEM cell could be put to use to combine a desired signal (12dB SINAD reference) and undesired noise spectrum (rejection notched at desired) from an amplified noise diode generator to perform a Noise Power Ratio test of these various radios having integral antennas. This set up could be used to quantitatively measure radios and rank them on a dB scale of best to worst. 

 

This setup would simulate the "real world" environment of powerful emitters in and out of band of the receiver.

[gman1971]

Well said. 

 

Many years back, before these CCR became the rage, it was a common complaint of ham users of Japanese handhelds that when replacing the factory supplied "rubber duckie" antenna with a 5/8 wave dipole or a base station antenna that the receiver sensitivity would erode. 

 

This was quickly identified as being a combination of both poor RF front end selectivity and poor dynamic range and IMD .

 

It would be interesting to subject these CCR radios as well as known good commercial grade radios to the rigorous testing of TIA603D.

 

Lacking the complete facilities to do so, it occurred to me that a UHF TEM cell could be put to use to combine a desired signal (12dB SINAD reference) and undesired noise spectrum (rejection notched at desired) from an amplified noise diode generator to perform a Noise Power Ratio test of these various radios having integral antennas. This set up could be used to quantitatively measure radios and rank them on a dB scale of best to worst. 

 

This setup would simulate the "real world" environment of powerful emitters in and out of band of the receiver.