Flameout

I was hoping I'd get lucky, but I guess not. I have no idea where to even get it tuned properly so for now, it will be sitting on a shelf. Just for the heck of it, I attached a dummy load to ANT and connected my comet CAA-500 Mk II analyzer. I'm sure this is in no way an accurate test, and probably completely irrelevant, but the best SWR, which was about 1:1 at 50 ohms was 454.600 on the LOW port and HIGH was 468.200

I was initially using two Kenwood 880 radios. Now using one 880 as the RX radio and using an Icom F6011 as the TX radio. The SWR from the 6011 going directly to the antenna is very good. Around 1.2 and about 44 watts. When I put the meter between the 6011 and the LOW input of the duplexer, it is crazy high swr. With the meter between the ANT output of the duplexer and the antenna, swr isn't bad, but power drops to about 8 watts. A big difference from the 40+ going in. The duplexer is a chinese Fumei, tuned to 462-467. Never was tunned to a specific frequency. I just went back to using two antennas for now and working good. If I can ever figure out this duplexer, maybe I'll give it another shot

I'm sure many of you are getting tired of my questions, but I have one more, for now ? I was attempting to put together a portable repeater system, using two radios and two antennas. That part worked out fine, and the repeater was working. I decided to try adding a duplexer into the mix and just go with one antenna. Again, it seemed to be working ok, other than the duplexer absorbing more than half of the power from the TX radio. I was curious about the SWR between the TX radio (462.650) and the LOW side of the duplexer so I checked it and was surprised by the results. It was well over 20:1 (but between ANT output of the duplexer and the antenna, it was normal - about 1.2) Is that normal swr to have between a TX radio and duplexer? I disconnected everything for now, until I know for sure. Google was no help at all as I couldn't find any info on that specific configuration of TX to duplexer. Maybe I somehow fried the duplexer?

yes, I do have the original codeplugs from all of the radios. Not that I understand that Fleetsync programing though. Saved as a .SDT and a .DAT file. I couldn't find any frequencies in there though, showing what they were programmed at. Voltages all stay consistent when transmitting. I'll read through that Realingment section a few more times. Eventually it might make sense lol Even though these radios are listed at 450-490 MHz, they can still be programmed in the 420-450 MHz 70 cm bands?

Yeah, I'm up to 6 - 880's now. Well, 5 1/2 would be more accurate. Three of the 880's and 3 - 880H's I tried testing with two different power meters. One is the MFJ-847 and the other is the SW-33 (I don't see any other name on it) They are both pretty close in their readings, but I think the MFJ is a little more accurate. I have a dummy load, but it gives me worse SWR than the antenna does! Just on example of my tests. The 880H with that BNC connector gave me 18.1 watts and SWR of 1.38 on 462.650 and the other 880H was same SWR but 25 watts (25 was the max I got out of that radio and the most I got out of the "bnc" radio was 18.2 watts. With the same tests, I get much more power out of a couple of old Icom radios. F2821 and F6011. They are listed at 45 watts and put out around 42

I couldn't make heads or tail out of that when I tried looking up in the service manual. I was checking it for any voltage and also connected an swr/watt meter with zero results. Makes much more sense now. I actually picked up two of the 880H radios, and checking the power output, I'm barely getting 20 watts on high power Thought someone might have swapped the 880H boards with 880 boards, but when I opened them, they both had the 45w PA (although completely different from the RA45H4452M in the original 880H I started the thread with). What causes the diminished output. Just old radios? Kind of disappointing to not get the output I was hoping for

This is were the BNC is connected to on the board. I'll try doing some testing later.

I removed the voltage regulator and put in a new one. When I had the old one out,, I realized the board was pretty bad. Looked like part of the of foil on the board was folded over. I cleaned the board best I could, put in a different voltage regulator but no change (the fibers in the photo are probably from the qtip I used to clean) Meanwhile, I picked up another (very clean and working) TK880H, but this one has an N connector for antenna (did they ever come from Kenwood this way?) A wire with a bnc connector and a factory 15 pin plug. What would that bnc connector be for?

I did those tests and nothing at all on pin 1, 2, 3 0r 4 when set to Voltage AC. Went back to DC and did the same test. Keying the mic gives 0 on pin 1, 1.7 on pin 2, pin 3 is the 13.8 so no change there, and pin 4 was 1.5. Of course still Zero watts and zero SWR. I'll keep playing around with it. Maybe I'll get lucky

I checked the voltage regulator on another 880 and it was basically the same. 13.8 and 7.94. I'm looking over the board now with strong magnification under a bright light.(I will probably need some Tylenol after this) I took the board out of the case, so the photo is the part that was hidden by the case. Is that white stuff normal or are those components failing or already failed?

oh wow, ok. I just read through the data sheet again (I may have to read it a few times) I just checked that voltage regulator that I put in. It was showing 13.8v / gnd / 7.88v so pin 2 of the PA is getting that 7.88 from the volt reg so I guess I can start from there, or should it actually be 6v? I guess the 17v is like the maximum? At least I can hold off on buying a new PA for now. I know I'm probably putting more into this old radio than it is worth, but it's kind of fun trying to figure it out

Thanks for the link. I'm getting a nice little collection of Kenwood TK-880 files. I checked pin 2 and 3 and only pin 3 was gettting power, so maybe the PA is good after all. If I were to bypass everything and temporally supply the (13.6) voltage to pin 2 to see if the radio would actually transmit, would that do more harm than good? I guess I'll start tracing back and see if I can find the problem

Ok, thanks. Well that is well above my pay grade lol. I may take the risk and offer this seller $30. I just have no idea what else may be wrong with the radio. It powers up, programs, red light comes on when transmitting and green comes on for receiving and it is working ok as the rx radio in the repeater setup and sending that signal to the tx radio https://www.ebay.com/itm/403511558565?mkcid=16&mkevt=1&mkrid=711-127632-2357-0&ssspo=6B03kewjR7i&sssrc=2047675&ssuid=0zihXCkJQWG&widget_ver=artemis&media=COPY

Oh, I did have an antenna connected. I guess the power amplifier is the part that I have circled in my photos? Looks to be around $40 for the 40w, for the 880H. Not sure if it's worth the gamble. Is there a way to test the power amplifier that you (or anyone) know of? I guess that also affects the audio output?

Are the only differences (besides the obvious larger heat sink of the 880H) on these two radios just the RF MOSFET Amplifier Module and the extra voltage regulator on the 880? Am I missing something else? I bought a non working 880H and was able to get it to power on by replacing a diode, a capacitor and the one voltage regulator, but there is no audio and no power coming from the antenna, even though it is transmitting and receiving. I started looking at the two and those are the only differences that I see. Seems weird that the lower power 880 has the 2 voltage regulators where the 880H just has the one. Also, any idea why the 880 has no audio and no power coming from the antenna wire (I tried external speaker and had swr?watt meter attached to antenna wire with zero SWR and zero watt output - even though when I transmit, it is being picked up on an ht nearby) Another thing too, even though the display works on the 880H, the LED's don't Also, don't mind those extra wires. I was testing these radios as RX radios in a portable repeater

I was getting just over 5.7w from mine, and close to 11 when I checked before it went into the duplexer. I'd be a bit upset with that 2.27

Could I have that radio set on a repeater channel, say R21, and transmit 467.700 to a repeater and Rx back on 462.700? I didn't explain myself very well in the previous post,sorry. Just didn't want to screw up the duplexer if I were to TX into the low side which is meant for 462.xxx. Maybe I should just get another antenna

I was able to update the firmware of my nanovna (from 0.4.0 to 0.8.0 build date nov 25, 2019 to jun 19, 2020) so not sure if it's even the latest, now to work on checking the duplexer, but I do have another question. The two TK-880's that I'm using as my portable repeater, can I still use the Tx radio of the repeater to transmit on? Of course it takes it out of the 'repeater' configuration. For example, I still have it programmed with the GMRS channels, but when using it as a repeater, I have it set on channel 19. Can I just plug a mic into that Tx radio and use it, transmitting while it's still connected to the duplexer? Reason I ask is that it is receiving much better on the antenna connected to the duplexer than a small junk antenna connected to my other GMRS radio. The photo is how I have it set up, and the radio on the right is the Rx radio, which is still programmed to the GMRS channels

I was able to get the software up and running on my laptop (win10) but unfortunately can't get it running on my shack computer (win7) First things first, I need to work on updating my older nanovna. Running version 0.4.0-3-ge04d3af from Nov 25, 2019 and as soon as I can figure that out, I'm going to give it a shot at seeing if I can figure out where this duplexer is tuned. Right now I have it up and running on .650 and seems to be working ok. Can this cause interference on say .625 and .675 if it wasn't specifically tuned for .650?

Thanks for that info. There was a video on you tube where someone used that same spectrum analyzer that you linked to. For that price, I may have no choice to to buy one, or something similar haha. The ebay link was also showing a few others. I initially was just building a portable repeater that I could take camping, use in emergency etc but it's easy to get carried away. Although the repeater was working ok using two antennas, adding the duplexer and going with one antenna I thought would be easier. So I now have the cheap Fumie duplexer which I didn't have tuned but says 462-467. I was just curious as to what they actually tuned it to.. I haven't tired it yet as I needed two more N connectors. Really appreciate the help and advice from these forums

I'm going to have to learn this VNA a little better first. I'm kind of lost at what you are saying. I bought this thing over a year ago, but never really got the hang of using it

Ok, thanks. I'm gonna give this another try. I got these numbers but I just had the nanovna connected to low then high. 463.860 and 464.280. It said it was tuned to 462 -467 so I guess I should expect something closer to that

Is there a way to check a duplexers high and low preset using a nanovna? I realize you can tune one this way, but thought maybe there might be a way to find this info. You tube wasn't much help

Ok, thanks. I certainly don't have the equipment to tune one of these things. Seems I have (lots) more reading to do. I have no idea if they are br/br or bp/br but one was a Fumie the other I didn't see a name. Both from China of course so certainly not high end duplexers. I just made a portable repeater out of two Kenwood 880's and it's working ok with separate rx and tx antennas but thought it might be easier with just the one antenna. This isn't something I planned on operating 24/7. Just traveling, camping etc. And I imagine a duplexer would take away some of the power from the TX radio. It's putting out 24 w right now so a duplexer would probably take half of that. Been looking for an 880H, for that little bit more power, but the ones I've found must have gold bars stashed inside

I'm sure this has been answered, but I can't find it. (Sure are lots of results when searching duplexer) If a duplexer says it has been tuned for 462-467 does that mean it will now work on all of the GMRS repeater frequencies, or does it need to be tuned for a specific frequency, like 462.650 - 467.650? I asked a seller on ebay and they had no idea.