ft847 on 4 metres

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

Re: FT847 on 4m

Postby Ron G8ctz » Tue 23 Nov 2004, 22:15

You should also have copied my findings over. Here they are again.
THERE IS NO INCREASE IN SIGNAL TO NOiSE , you are fooling yourself
FIGURES :- 70.2Mhz hidden gain(probably calibration ask Yaesu)set at FF .6uV input SINAD = 10db gain set at 52 .6uv SINAD still= 10db NOchange . the S meter shows on ssb a change in reading from S6 to s3
For comparison on 50 Mhz .201uVgives 10db SINAD , and .6uV gives 23db
2M and 70cmsimilar to50 Mhz . These figures were obtained using a calibrated professional radio test set from Marconi.
Full figures for all bands are available.

PS adjustment of any of these hiden settings does not give better S/N

G6GVI wrote:I've copied this over from the old 4m Forum..

Increasing the 4m sensitivity on an FT847

Reference 847 being DEAF, it is (or WAS) on 70mhz. Internal RX Gain is set very LOW!
Ive set mine to maximum and its brill on the band now with NO side affects.
set 847 to 70mhz band ssb. TURn off 847. Hold down all 3 buttons on mic (hard) and switch rig on. U should now now see a new(hiden) menu displayed.
Rotate the SUB_Tune control clockwise until RX-GAIN is displayed.
now make a note of the 2 small hexadecimal digits on end of freq readout. prob 50 or so, rotate the mem/vfo ch, control until desired rx gain increse is acheaved. I set mine to Max FF. press MENU button to store. switch off repeat process to ensure settings were saved. This adjustment is band selective, so u can do same to any other bands which are a bit low if desired, and u have NO loud local stations. Hope this helps. regards mike g4vpd

There should be some activity on Sunday 6th June, during the WAB 4m Phone contest. Mark G0OID and I will be out on the hills - hope to hear you Alwyn.
73 de Ross G6GVI
Ron G8ctz

Postby G6GVI » Mon 10 Apr 2006, 10:10

Keith G4FUF has just updated his technical feature on modifications to the FT847, to improve its performance on 4m:

He now shows how a three-fold increase in output power may be achieved with a bit of ferrite and a dab of glue, and proposes developing a miniature PCB for an RF pre-amplifier.
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Postby G6GVI » Thu 13 Apr 2006, 08:10

Thanks to Graham G8HVY for the following supplementary information about the FT847:

The basic information about serial numbers is correct, however the month codes start from 'C' for Jan and end with 'N' for Dec. Neither 'A' or 'B' are used as month codes.

A word of caution should be included in the article from Keith. I have a lot '16' FT-847, date code '8L' and while the 'L5005' mod reduced the current drawn from around 17A to approx 8-9 amps, the output seemed to remain at 10W. Well almost!! Although the output power measured on an analogue meter read 10W, however if you look carefully at the output meter on the FT-847, the initial power peaked at around 20W or so, which was enough to take out the PA transistor on my BNOS 100W PA.
The MRF492 failed after reconnecting the amp after the modification.

While I fully support the efforts of Keith, as noted in the article, bear in mind that the performance verification can only be guaranteed on the serial numbers of the sets actually tested and not all batches. Yaesu's inprovements on the performance of the FT-847 for 70MHz were constantly changing and not all mods were doumented and available as public domain info 'such is the policy of Yaesu' to restrict Technical bulletins to within their group and not make them available as open release documents.
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Postby G6GVI » Thu 13 Apr 2006, 19:04

Further info from Keith G4FUF:
The earliest 847 I have modified has S/N "9E", this being my own and the testbench for all mods. This model still had the wire mod to the "50 MHZ" forward power pot so I would assume earlier models are the same.
As stated in the article, you must remove this if you do the mods for the power output to increase because the ALC is holding it back to the original lower level. So as Graham describes he still sees 10W output but at higher efficiency.

The 847 has a good history of zapping preamps and other kit because the type of problem Graham describes occurs on many 847's.
They can produce a full power blip on initial TX regardless of the power output control or in the worse cases they produce a full power TX pulse when you switch the radio on via your power supply rather than the front panel switch. It's a software initialization problem as supply volts come up slowly. This fault can also occur with the classic relay chattering problem if the DC supply idles around 11V momentarily.
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G4FUF mods

Postby G4ZFQ » Wed 19 Apr 2006, 13:52

G6GVI wrote:Keith G4FUF has just updated his technical feature on modifications to the FT847,
He now shows how a three-fold increase in output power may be achieved

As I probably will not do anything more for a while I thought I'd tell of my preliminary look at this mod, to do all the checks requires quite a lot of dismantling!

Mine is an early one s/n 8Fxxx. So may be a bit different.
It has had a new (CPU?) chip fitted for two way CAT.
There is no wired connection to the "50" pot. Edit:- 22 April Wrong! There are 3 resistors wired in around Q3048 beneath the RF board. Presumably this is what Keith is referring to. No silk screening under the board, circuit tracing will take some time!

Changing the jumpers did require a reset before any change was noted.

Original power 25W at 20A on my meters.
After trying 5 different VHF cores the best I could get was 40W at 17A.
Obviously an improvement, but not as good as Keith got.
However, with that core the 50MHz band was compromised. It is now about as inefficient as 70MHz. There is more drive available but it draws 20A at 50W output, it will go higher but the psu is driven into current limit at 25A. (Thankfully!)

From Keith's remarks it seems the choice is either 70MHz or extended HF coverage. Many seem to be using the 847 on 70MHz with the wrong jumper settings. I have not yet checked the BPF selection, there are no test points on top of the RF board. I assume it is correct as I am back to the original jumper settings.
Last edited by G4ZFQ on Sat 22 Apr 2006, 16:00, edited 1 time in total.
73 Alan G4ZFQ
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Postby G6GVI » Thu 20 Apr 2006, 16:14

I've posted some more information from Keith G4FUF, regarding ALC and power limiting in the FT847:
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847 on 4m

Postby G4ZFQ » Thu 4 May 2006, 09:30

g4mdc wrote:Are we more or less agreed yet that the only thing that is right (+/- 2.5kHz or so) about these on 4m is the frequency on the display?

Out of the box they are usable at low power with caution.
Yaesu's implementation of 4 metres is not one to be proud of but it just works and seems to have increased interest of 4m.

Keith's articles have shown that Yaesu's errors can be at least partially overcome by someone prepared to do a few fairly simple checks and modifications.

My checks on an earlier model have shown differences in the radio but that it is also able to be improved.

I have not operated on 4 m for a long time, when I did I found 30 watts to an HB9CV was adequate for SSB (and a bit of CW). In 1986 I got the GB4MTR award without working any of the special stations. I would encourage anyone to be content with that sort of power.

With regard to the frequency display, (And stability) that can be greatly improved. I have fitted Khune crystal heaters to the reference crystal and the carrier insertion oscillator. I have not finished checking and adjusting this. At the moment after a few minutes it is stable within a few Hz on receive, reading about 30Hz low. I have noticed a transmit offset of about 100Hz which needs attention.

The 847 is a convenient way to have access to 4m, any other way means more equipment and home brew for anything other than FM.
The 847 is not for those that want the ultimate but it looks as if it can be made adequate.
73 Alan G4ZFQ
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Postby G0EHV » Mon 9 Oct 2006, 18:47


Well, finally got around to trying the mod for higher power on my 847.
S/N is 8G, so quite old and max power on 4 was only 9 Watts, drawing about 14 amps.

Core used was quite a large one, about 9 mm long and about 4 mm in diameter. Fitted fine and result was a slight improvement in efficiency - current drawn now is 9A for the max 9W output.

Cut the brown wire, result was 50W out with 20A drawn.

Tried adjusting core in/out of inductor but no improvement found, in fact some degradation of 70 MHz and 50 MHz, so must have got lucky first time!

Final position is that 50 MHz has become less efficient, needs to draw 24A against original 17.5A for 100W out.

Looking at the physical layout I thought I'd remove C5123 on the LPF but decided that the de-soldering etc was not worth the effort/risk! Can anyone suggest a simple way?

Probably will still use my Spectrum transverter as my first choice but the beauty of a single box solution might lead to some /M operating :)

Thanks to Keith G4FUF for comprehensive mod info and for finding the initial "gem" :wink:

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Getting at the PA board on the FT-847

Postby G0EHV » Mon 16 Oct 2006, 11:28

I have not done the inductor mod as yet and would appreciate any info or tips on stripping the radio down to get to the inductors location.

Very easy to get to PA board -

1 Remove covers.
2 Turn radio upside down, you will see main board (the one with all the rear connectors).
3 Remove screws holding main board, 4 ISTR. Slide board forward and hinge up.
4 You should now be looking at a shiney tin plate screen. Remove screws and lift clear. Voila!

Putting it back together is the reverse. Remember that the main case screws are hole specific - if you use a long screw in where one of the short ones came out you will damage one of the connectors.

Good Luck,
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Postby G6LBQ » Sat 21 Oct 2006, 18:46

Hi Guys...

Thanks Eddie for the info on stripping the radio down and locating the L5006 coil to do the PA mod.

Having snipped the ALC wire and tried various ferrite cores in L5006 I have obtained 75 Watts regardless of which core I use...


With a ferrite core inserted in L5006 the coil gets stinking hot, to hot to touch!

This is worrying as its getting so hot it would burn my finger if I left it on for more than a sec.

In transmit on 4MTRS the radio is drawing aprox 20 Amps according to my PSU.

I note that in G4FUF's mod details he experienced that the coil got warm after the radio had been used for a while but my coil gets very hot in a matter of seconds so much so I fear it could bake the solder on the coil at the PCB!

Anyone any ideas or suggestions and how hot do your own L5006 get?


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Postby G7CNF » Sun 22 Oct 2006, 06:57


I have written a long scrawl about this in a snail mail letter to some amateurs with no internet connection. Basically the permeability of the core is critical for this application. In my letter I expressed concern that there may be some less experienced amateurs with little or no previous engineering or homebrew experience who will have undertaken this mod blindly, using cores from 70/10Mhz/455kHz IF stages.

These cores will get exceptionally hot due to the high flux density present in the centre of L5006 and there will probably be a few 847's knocking about which will start to rattle soon!

This is why Keith used the Toko VHF/UHF core, which has a relatively low mu compared cores found in lower frequency IF stages, which is where I suspect many of the ferrites will have come from that have been installed in the rigs. If you have an LCR meter, bridge or SWR analyser, it is possible to check your available cores and roughly calcualte the mu, this would save much heart-ache. What may be harder to determine is the impedance @ 100Mhz, which is also a critical factor, as this quality will determine the level of heating.

The only satisfactory way to complete this mod is with a core of known low mu, a GDO, some patience and thorough temperature testing. (And preferably a speccy also).

One final thing I will point out. It is interesting to watch a spectrum analyser as the inductance is varied in this stage...... Remember, there are numerous iterations of the 847, and early models in particular need observation with a spectrum analyser when dealing with 70Mhz TX.... Lets hope Ofcom don’t get too many complaints……

73 de Nige.
Last edited by G7CNF on Tue 5 Dec 2006, 15:00, edited 1 time in total.
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Postby G6GVI » Tue 14 Nov 2006, 16:30

A new feature article provided by Nige G7CNF has been added to the Technical Articles section:

This includes some detailed measurements on an FT847 operating on 4m, and suggests a modification to reduce the high-level spurious signals found.

I just hope that Nige's set is not a typical example!
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Postby G6GVI » Wed 13 Dec 2006, 14:33

The latest information suggests that the problem with Nige's set should not be typical of UK "C-2" import versions:
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Postby G7CNF » Wed 13 Dec 2006, 15:32

At this point, I think the picture is becoming as clear as mud. Further more I am wondering if Yaesu's brief intrepid venture into 4m has done many of us a considerable a disservice? I abandoned a perfectly good transverter for the convenience of an 'all in one' set, even if it does have deficiencies!

Graham's information is particularly useful but also shows why Yaesu's determination to remain a 'secret society' is so counter productive; with more openness this confusing situation could have been avoided.

If as Graham observed, region codes are being modified manually in this way, we really do have a problem on our hands. It is reassuring to know that there may be fewer sets affected by this malady, but less reassuring to know that the retailers we think we can trust to provide us with 'conforming' equipment may be deluding us into buying items which may not be intended for the UK market place...

I am sure this will result in a tirade of defensive remarks, but remember that it is our duty as amateurs to make tests from time to time to determine that our equipment conforms to our licence conditions. One of my radios did not comply and I have taken action to correct it; but also made the defect public so that others can take action to check.

Let's pool all the information we have so ensure that everyone with an 847 can quickly and easily identify if their sets are of the variety that is likely to cause nuisance.

More information is needed regarding serial numbers, batch numbers etc to iron out the confusion.

Let's hope that my set was in fact in the minority.... Season's greetings to all. Merry Christmas.

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Postby G0EHV » Thu 14 Dec 2006, 15:57

As discused off the list, my 847 looks to be OK as far as the spurii are concerned.
Just come down from my loft, after seeking out the original box. Lo and behold is a "C-2" :)
As I said in the email to you it's a very old model, obtained from Lowe when they had a shop at Newcastle airport!
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