Yaesu FT-847 Modification Manual Download Page 18

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In effect, we will have clean place to mount new filter with LNA.

After inserting and soldering filter module we need only to make two wire bridges from
diode switch to make it working. It’s clearly shown below.

Of course it’s good to check with any multi meter if no sudden short circuits

accidentally were made.

Last thing we need to do is cVcc on filter PCB to nearest SMD 22uF

capacitor giving us +8V to feed the LNA on RX.

Summary of Contents for FT-847

Page 1: ...iginal filter in the 847 has bandwith of 54 76 MHz which should give reasonable RX quality But it s not Receiver sensitivity varies from about 0 3 to 0 5uV depending on the production model and Year o...

Page 2: ...ion of the modification includes more than 30 TRX across the EU and probably worldwide which can assure that the solution is repeatable and effective To achieve these results filters should be made ac...

Page 3: ...mm dia FTP ethernet cable should be good idea to get this wire in good isolation Filters base should be prepared in advance This should be done by removing the legs cutting any flanges and drilling ho...

Page 4: ...ted against short circuit we can put the screens and solder terminals Final result can look like this On the project stage I had made some measurements using NWT500 Please note the attenuation frequen...

Page 5: ...Close up image And this is the screen from measurement taken prior to filter modification FT847 signal spectrum with 10W output power...

Page 6: ...king our transceiver Although this has not been proven empirically and many rumours are about is it true or not the authors of this article after hearing about four or more different cases of damage t...

Page 7: ...gnals 45 600MHz 34 dBm 49 035 MHz 2dBm Transmitter measurements made after the modification of the track TX 10W power out QRG 70 1MHz QRG 70 100MHz 39 dBm Unwanted signal 45 600MHz 22dBm below 70MHz C...

Page 8: ...of adjustable gain by changing the bias voltage of the first gate G1 by small potentiometer which may be replaced by a fixed resistor in some cases Coupling coil consist of 3 turns of 0 5 mm insulate...

Page 9: ...Measured response of amplifier with 30dB attenuator NWT500 not calibrated...

Page 10: ...of 0 12uV MDS and the TX power at almost 60W level with dramatically improved purity of the signal spectrum and efficiency of your TX Disclaimer The following article is for information purposes only...

Page 11: ...5 2 x 47p SMD 0805 C7 C9 2 x 56p SMD 0805 L1 L3 2 x 2t Cu 0 5mm with isolation L2 L4 L6 L8 4 x 6 5t CuAg 0 5mm L5 L7 2 x 3t Cu 0 5mm with isolation Q1 1 x BF994s SMD SOT143 R3 1 x 10k PR R6 1 x 10k SM...

Page 12: ...ndpass filter to modified one with LNA replace existing TX filter chain to sharper one to get clean signal Let s get it started 1 Unlocking your FT847 to get 4m for those who already have unlocked one...

Page 13: ...th Isopropyl Alcohol IPA It will ensure that joints are clean and no any solder dust left on place You should end with similar result for version b mod 2 Next step will be increasing efficiency of Pow...

Page 14: ...rews Then we should disconnect two HF outputs on the rear Be careful as these pins need to be bend a bit to suck the solder out At this point please look carefully for two small bronze spring soldered...

Page 15: ...ted on two different 847 After cleaning the place You should get something like that 50 Job is done now But At this place I will propose that if we already made efforts to remove this PCB we should do...

Page 16: ...f PA job another good idea As observed in all four 847 after some years of time beryllium oxide paste used as heat spreader on transistors is getting dry and hard NOTE I found that in 847 year model 8...

Page 17: ...tors After removing PCB we will have access to TX and RX filters To do this mod we must remove almost all SMD capacitors and coils Which one Look at the picture part of service manual It will be easie...

Page 18: ...d only to make two wire bridges from diode switch to make it working It s clearly shown below Of course it s good to check with any multi meter if no sudden short circuits accidentally were made Last...

Page 19: ...we can see TX filter part If Any trouble finding it please refer to PA1O article This should look somehow similar Green SMD were omitted by Yaesu those are the caps marked with an asterisk on schemati...

Page 20: ...After some cleaning PCB will look like this damned Japanese glue Next step after inserting and soldering the filter is to make two bridges similar as in RX chain...

Page 21: ...meters final result depends on fact if there was any attempt to modify RX gain It will be good to get into service menu of the RIG and check RX CHAIN parameter and correct the gain if needed Standard...