ft847 on 4 metres

Questions and answers on 4 m transceivers, transverters, antennas, etc.

Postby EI2GLB » Tue 20 Jan 2009, 04:54

Hi All I have a few questions, To do the PA1O do you have to remove the PA board/transistors. and how much of the radio do you have to dismantle to get at the Caps that need removing.


and i have read the article many times before someone says it!
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Re: FT847 tx filter

Postby G0KSC » Sat 31 Jan 2009, 16:10

G4FKI wrote:I managed to get in contact with G4FUF, unfortunately the tx filter is unavailable due to a lack of response for the item.

Blimey, you managed to get a response to email from Keith! After I eventually received my Preamp board (end of summer ordered at the begining of the summer) , I have not had a reply to mails since. The last mail was asking for a price and availability of a fully built preamp too.
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Postby G8HVY » Sat 31 Jan 2009, 18:10

Hi Trevor EI2GLB

If you read the post by Ian G5WQ on the page 3 of this topic there is a good description on how to gain access and to remove the board to do the modification, remember that is best to remove C5050 390pf and not the 470pf capacitor if you wish to retain the max power output on 6M.

Best of luck

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yaesu ft847 4meter mod

Postby 2E1HJS » Sun 6 Dec 2009, 19:05

Hi to all i am new to this forum can any one tell me if this PA1O mod work on my radio it as got serial 3J810005 and on the box it says A11790021 type C2
gratefull for any help
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Postby G8HVY » Sun 6 Dec 2009, 22:06

Yes the PA1O mod will work with your FT-847, C2 is the UK version so the TX filter mods are factory fitted, your set was manufactured in Aug 2003 so it is a reasonably late version.
You will just need to remove the Capacitor on the TX board as described by PA1O however it is better to remove t C5050 390pf capacitor if you wish to retain the maximum gain on 6M also don't forget to unsolder the wire that limits the power to 10W on 4M.
It is best to check the power consumption on 4M before and after removing the capacitor and note the difference, before clipping and insulating the wire that limits the set to 10W on 4M.
I have removed the 390pf on 5 radio's with good results on 4m up to 85-90w on 4 with 13.8v at the dc input socket.
If you note a lot of voltage drop on the DC lead you can experience lower than expected output (cable and fuseholder) volt drop can be significant, the later multi wire cables with blade fuses tend to be better.

Good luck

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yaesu ft847 4meter mod

Postby 2E1HJS » Sun 6 Dec 2009, 23:35

Hi graham thanks for the info. you mentioned clipping the wire can you explain or photo of the location for this wire. and do you know best place to buy the preamp mod for receive
hope to ear from you soon as keen to get setup on 4 meters
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Postby G8HVY » Mon 7 Dec 2009, 14:02

Hi Roy
Details of the wire to remove are here
however as your radio is a later version you may not find this transistor as in the picture, later sets had the transistor built onto the board and
the wire is soldered to a pad on the circuit board. The RF board is located under the loudspeaker, if you look at the picture in the above link the vacant 2pin socket is where the L/S is plugged into this should help with locating the area to look for.
Regarding pre-amps Keith G4FUF offers a kit see item 4 down the page here
also Tony CT1FFU is offering a pre-amp which he sells on Ebay
It is not clear in the details from CT1FFU if the PA1O RX filter modification is required before fitting his unit.it might be worth checking first. link here
as your FT-847 is a C2 version ignore the details on the TX filter details.
I hope this helps.

73's Graham
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Pre-amp notes

Postby GI0GDP » Thu 10 Dec 2009, 12:38

Yes it's unclear if the filter mods are needed, however the docuentation with the MAR-6 pre-amp shows it clearly fitted into PA1O new values.
However for what it's worth the sensitivity goes from -111dBm to almost -120 dBm for -12 dB Sinad when it's fitted with the filter values as fitted.
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PA1O mods and CT1FFU's 70mhz pre-amp

Postby CT1FFU » Thu 7 Jan 2010, 15:41

Hello To all.
If you using my preamp for 70mhz you can also make the Mark´s PA1O modifications on the pre-amp, no problem.
However PA1O pre-amp will increase the performace and sensibility of radio, due it´s better calculated to serve 4m band. so if you using both mods you might finde too much gain.
You have several options: for start, dont use the local build in FT847 pre-amp; put a atenuator on MAR-6 input (smd resistor) or go to hiden menu and reduce the gain on 70mhz menu.
Best 73's

Tony www.ct1ffu.com
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Postby M0AFJ » Fri 8 Jan 2010, 10:49

I fitted one of Tonys' pre-amps and it works FB, a big improvement. I do turn off the internal pre-amp as recommended.

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BPF Pin Diodes

Postby CT1FFU » Fri 8 Jan 2010, 19:48

Hello all.
another good mod and with a funtastic results is change the 4m BPF pin diodes D3059 and D3071.
Unfortunaly the original Pin diodes used by Yaesu are very poor.
I used BA482 but any good VHF low residual capacitance will do better job there then the original ones.
Choose any you like or finde.
If you whant, you can also change all pin diodes on HF.
The radio performance, sensibility and noyse will be incredibly better.

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Postby OH5NXO » Sat 9 Jan 2010, 18:14


I have (actually a friend has) FT-847 which puts out about 20w on 4m and I0JXX linear amplifier which wants 8w on 4m/6m and 5w on 2m. There has been smoke already...
I haven't yet measured the 847 output on 6m. Probably more than 20w, to complicate things...
How would you best attenuate the 847 ? I can think of

1) just be careful with RF drive knob. Leads to a disaster eventually.

2) Wire external ALC. One extra connector to remember, difficult to switch bands between 2m/4m. Fiddly millivolt levels to work with.

3) adjust internal ALC preset trimmer in 847. Limits output also when running barefoot.

4) attenuator resistors into amplifier, full 847 RF drive. Handy SMA-connection available inside the linear. This looks like a good solution.

How does the initial power spike (if any?) behave in cases 1-3 ? Is 847 cleaner if RF drive knob is reduced from fully clockwise position?

In the Linear/Tuner-connector, I keep the 847 "TX INH" inhibit high for about 100msec at beginning of TX. Does this quench or just delay the power spike ? The Linear-connector provides also "DATA IN" and "DATA OUT". Does anyone know what these are for ?

Questions questions :)
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Postby 2E1HJS » Mon 11 Jan 2010, 14:54

Hi to all can any one help me my radio started smoking on 4metrs on transmit when i look in side i found L5022 i think this is a toroidal inductor 100NH was nearly burnt to a crisp can any one tell me what part is and where to buy one do not know the tactual size of the core
hope this makes sense
grateful for reply
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USA FT-847 working without mod?

Postby NZ5N » Wed 14 Apr 2010, 12:08


I am a USA ham with a summer QTH in Slovakia. After reading that Slovakia has authorized 4m operation (although just 10w) and that the FT-847 can work on 4m, I got interested in this band.

My FT-847 is not a UK model and has not been modded in any way, yet it seems to be transmitting on 4m with about 20w output. Is this normal? The serial number starts with 0G.

If this works, I'll bring the FT-847 with me this summer and try to make some QSOs on 4m.

Thanks for any info.

73, Bill NZ5N / OM9ACA
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Postby G8HVY » Wed 14 Apr 2010, 14:04

Hi Bill
Unless you carry out the TX bandpass filter modification you will find that there is almost as much power out at 45.6Mhz as on 4M see here http://www.70mhz.org/ft847_g7cnf.htm
the BPF modification by PA1O will sort out the problem also the RX BPF modification will improve sensitivity.
See here http://www.vlemmings.com/PA1O/
By removing either C5050 or C5051 the efficiency of the PA ca be improved dramatically see also details from Marc PA1O in the link above.

Good luck on 4M great band.

73's Graham.
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