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Power loss
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I am primarily a CW op and use the FT-857 as my base station.? Lately while using the 857, the power will immediately reduce down to close to zero but I can still hear myself keying..? There have been several times when I was in a CW QSO and the power dropped down to zero (about 1 or 2 w estimate), and I continued my QSO although I was told my signal had dropped some.? In my headphones, I don't notice any change in my keying.? I have checked SWR at the same time and it remains about "0".? I use the MFJ Versa Tuner and the forward power will noticeably drop down and the reflected power doesn't change (always at 0).? Then after a while it may just come back up to full power (100w) and remain for a while or go back down, and come back up or just stay down.? Then after a while, it will work ok until it drops back down, etc.
What is going on with my unit?? Has anyone else experienced this problem? |
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Is your cooling fan running ok?
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-- Leonard K. Pennock (AD7AS) On December 17, 2020 4:00:20 PM MST, k0bwq@... wrote: I am primarily a CW op and use the FT-857 as my base station.? Lately while using the 857, the power will immediately reduce down to close to zero but I can still hear myself keying..? There have been several times when I was in a CW QSO and the power dropped down to zero (about 1 or 2 w estimate), and I continued my QSO although I was told my signal had dropped some.? In my headphones, I don't notice any change in my keying.? I have checked SWR at the same time and it remains about "0".? I use the MFJ Versa Tuner and the forward power will noticeably drop down and the reflected power doesn't change (always at 0).? Then after a while it may just come back up to full power (100w) and remain for a while or go back down, and come back up or just stay down.? Then after a while, it will work ok until it drops back down, etc. |
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Willard Morton
Phil, K4PO? Thanks for the suggestion, I haven't checked voltage but will monitor it as I transmit and see if I can learn anything.? In the meantime, I will check all connections and fuse.? I bought this radio new in 2004 so that is a possibility.? I will let you and the group know my findings. Leonard, AD7AS Yes, the cooling fan runs a lot.? But thanks for that suggestion. I appreciate the time you both have taken to respond to my problem. Thanks and 73 Willard Morton? K0BWQ
On Friday, December 18, 2020, 11:00:32 AM CST, Philip Salley <pcsalley@...> wrote:
Willard, The first thing that comes to mind is the 12VDC power reaching the radio is falling off as you transmit.? This is often caused by power line fuse corrosion or other poor connection.? The 857 is notorious for line fuse holder poor internal connections.?? Regards, Phil / K4PO |
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Check the voltage at the radio as stated above, but set your meter to read the ALC and see if that value changes and also the SWR.?
In the radio the ALC voltage controls the power of the output and could possibly cut back the power if there were a problem with an incorrect signal affecting it. Of course you could have an intermittent in the transmit chain or the drivers and finals. A problem with the antenna between the tuner and the radio could also be possible as well. J.D. KE4MD |
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Willard Morton
J.D. thanks for your suggestions, ? ? My voltage is steady at 13.8 on receive and drops to 13.2 on transmit and stays steady even when the power problem occurs. ? ? The SWR remains at 0 even when the power problem occurs so no change in this value. ? ? However, the ALC drops to "0" when the power drops down to about "0".? This is the first indication of a related change noticed.? Do you have an idea what the drop in ALC means? ? ? My antenna (dipole) is in my attic so do not believe there has been any change when looking it over.? The feedline is 300 ohm twinlead which goes down directly to my Versa Tuner wire balanced connector (no balun or switch).?? I really appreciate you taking time to respond with these suggestions.? I believe that you have identified the source/cause of the power problem.? Now do you have a fix for this, or what is your recommendation?? I do not have any test equipment so if it requires any part replacement, etc, I will probably have to send it off to someone to repair it.? But at this point I believe I can point to a probable cause.?? Thanks again and very 73 Willard Morton K0BWQ
On Saturday, December 19, 2020, 07:02:36 AM CST, J.D. Barron <jeter.d.barron@...> wrote:
Check the voltage at the radio as stated above, but set your meter to read the ALC and see if that value changes and also the SWR.? In the radio the ALC voltage controls the power of the output and could possibly cut back the power if there were a problem with an incorrect signal affecting it. Of course you could have an intermittent in the transmit chain or the drivers and finals. A problem with the antenna between the tuner and the radio could also be possible as well. J.D. KE4MD |
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Normally the ALC increases with the drive signal to the point where the audio is over driving the power set point and then it limits the power. The ALC dropping is an indication that the drive or output is dropping due to something within the radio. If it is not SWR or over driving then it may be a problem in the driver, something loose or perhaps a filter or amp stage giving trouble,
If you have a scope that will let you take a look at the signal going to the drivers and the signal coming out you could see what is happening. Sometimes the crystal filter CF1004 could be intermittent.? I had a problem with the FET amplifier stage after the filter myself., but the power was very low and stayed low.? Do you have a problem on receive? the filters are used in both directions although in this stage not that amp. Does the power drop in other modes? FM for example? The FM and CW use a different transmit chain within the radio. I doubt it is an ALC problem from what you are telling me as it would usually increase or peg out if that was what was killing your signal. Best regards JD KE4MD |
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