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Talk back or moni
Greetings,
I was wondering and it is possible the question has been asked and answered, so I am sorry then. The FT 847 moni feature for SSB is nice. Is there a way to enable this feature for AM and FM as well so one can monitor his modulation? I had a issue a while ago that I thought was the radio but ended up being the desktop microphone. I was even thinking of seeing if a external modulation meter could be used. Thank you. 73' Mark? KC3TNO? |
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Re: Schematics?
Emitter is grounded.? There is another possibility. On one of the boards is a line of presets that control output power. It could be that the UHF one is faulty, but I have no idea how that circuit works, at the moment. There is a slim chance it has been turned right off, given that you have no history of the radio working on 70. ? |
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Re: Schematics?
开云体育Here is the datasheet for the driver module. ? You are up against it without basic RF test equipment! ? Q4001 drives Q4006, so you need to know if Q4001 is working ? ·?????? The Drive is up to 50mW, a hand held will pick this up, however, 50mW will give you 59+60dB, so if you are getting 3 Watts out of Q4001, you will still have 59+60! dB ·?????? Disconnect the 4003 and 4004, an ammeter can be placed in series from here, to measure and set the bias through it by VR4001. ·?????? With the link disconnected monitor the current into the rig, then TX on UHF the current should increase my 1-3 amps if so then Q4001 is good. ·?????? Measure the base of Q4006, it will be 0.7 to 0.75 Volts on UHF TX, if not you have a bias problem, If it is volts then Q4006 base emitter is O/CC or Toast ( check the emitter is going to ground!) ·?????? You need to measure the power coming in, 30-50mW is my guess, find a way of doing this, diode probe across 50hm resistor and a 0.1 Cap, should give 1.6V at 50mW ·?????? The service manual will set how to set VR4001. See below. ·?????? From pin 4 to the transistor’s base are the matching components from the 50 ohm output to whatever the transistor input impedance is ? If you have oscilloscope, you could try tracing the signal, but at 440MHz, you may not have much show up depending on the bandwidth of the scope! ? The variable resistors on the FT847 are known to fail, without Bias you will get very little out ? Keep in the loop. ? 73 ? Andrew ? ? ? ? ? ? ? From: [email protected] [mailto:[email protected]] On Behalf Of Max Donoghue ? Is there anyway with the crude test equipment I have I can check for RF on pin 4 of the UHF module? |
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Re: Schematics?
Ok, this is strange.? I am struggling to see how you can have 0.7 volts base, 13 volts collector, but no current. That makes no sense. Time to get a bit creative, and enlist the help of your wife. Try the signal in, signal out test with her using the handheld to RX at a greater distance. Then do the same for the base and collector of the final transistor. There's another couple of things to check, I may be insulting you here, but what is PSU TX current on 2 metres, and 70 cms? Are you just going off the meter on radio, or have you actually verified with a power meter and dummy load that no juice is going out, or are you just relying on the meter on radio? On Tue, 12 Jul 2022 at 23:28, Max Donoghue <ve3tmt@...> wrote: Hi Andy, |
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Re: Schematics?
开云体育Also put an amp meter in series with TPH and 4003 and 4004, that is what it is for, run around 10 Watts and see that to current ?is, at 50 Watts I would expect 10 -12 Amps depending on efficiency! ? 73 ? Andrew ? ? From: [email protected] [mailto:[email protected]] On Behalf Of Andy Bosworth ? A very quick look at diagram,? ? ? ? ? On Tue, 12 Jul 2022 at 16:01, Max Donoghue <ve3tmt@...> wrote:
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Re: Schematics?
开云体育You need to know the level, however, that sound relativity good news, The PA block may be obsolete, but tricky to test with limited equipment ? 73 ? Andrew ? From: [email protected] [mailto:[email protected]] On Behalf Of Max Donoghue ? Yes I can hear the UHF signal quite well on my handheld. But no output power shows on the 847's meter. This is probably the pre-drive signal I'm picking up. |
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Re: Schematics?
A very quick look at diagram,? you should have? 8 volts tx on UHF, pin 1 of J4007 You should have some voltage, less than 8, on Pin 2 of the module.? You should have 13.8 on pin 3 of the module, and RF out on pin 4. Check with handheld at varying distance/without antenna to see if it is amplifying. Check what voltages you have on base and collector of final transistor, Q4006. Should be around 0.65 on base SSB tx, and 13.8 on collector. On Tue, 12 Jul 2022 at 16:01, Max Donoghue <ve3tmt@...> wrote: Yes I can hear the UHF signal quite well on my handheld. But no output power shows on the 847's meter. This is probably the pre-drive signal I'm picking up. |
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Re: Schematics?
Do you have a vhf/uhf handheld? Use on same frequency, with a carefully positioned screwdriver tip on the input of the driver block. Will give a rough idea if you have drive to module. By going on the output of module, you should be able to see if? it is working. On Tue, 12 Jul 2022 at 14:53, Andrew Lenton <a@...> wrote:
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Re: Schematics?
开云体育No That is a network analyser, as it has reflection ports and through ports, it is not a spectrum analyser, they are different. ? 73 ? Andrew ? From: [email protected] [mailto:[email protected]] On Behalf Of Max Donoghue ? Looks about the same as what I have... |
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Re: Schematics?
开云体育Ah in that case, buy one of the those small software defined Spectrum analysers, and a few SMA adapters so you can put a scoop probe on it! Look at the single input on the VHF side the UHF will or should be a similar level! ? 73 ? ? ? ? Andrew ? From: [email protected] [mailto:[email protected]] On Behalf Of Max Donoghue ? I don't have a lot of test gear. Multimeter, small portable scope from Amazon and a NanoVNA. |
Mark Bowersox
Andrew Lenton
Andy Bosworth