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Do you have any idea why the FT-857D caught fire? I have one installed in my Toyota Camry and that report of a fire now has me as nervous as a cat trapped on a front porch surrounded by rocking grannies!

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.

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.

Put up a UHF Yagi as high as possible and pointed in the direction of the closest repeater and/or base station. I use a yagi here in NW Indiana to reach several repeaters on the north side of Chicago (about 43 airline miles) reliably.

Just on the off chance that we don't notice your thread, huh?

With so many good quality used radios from Kenwood, Motorola, Vertex, Icom and others, most Part90 and many Part95 certified, and selling for more-or-less the same price, I don’t really see the point in bothering with The RT76. Also the quality brand radios usually have a huge number of branded and 3rd party accessories available as well: speaker/mics, antennas, batteries, group charging stands, etc.