ft847 on 4 metres

[NZ5N]

Graham and all,

Thanks for the reply. I'm just getting back to this project, leaving for Slovakia on June 2.

I have looked through this thread, the PA1O page, and the CT1FFU preamp on eBay. I believe I have enough ability to remove the capacitor and to install the preamp, but I do not really understand the filter mod and not sure I can do it.

Is there any further info on the filter mod available? Or is there any commercial solution, such as a ready-made board that can be purchased?

73, Bill NZ5N/OM9ACA

[NZ5N]

Have not seen this discussed on this board, and not sure who bijkker is, but this purports to be an easy solution to the 847's poor reception on 4m:
http://cgi.ebay.com/ws/eBayISAPI.dll?Vi ... 0558175568

Anyone tried this kit? It seems to be different from the CT1FFU preamp.

I suppose this only solves the RX issue but does not deal with the TX filtering?

73, Bill NZ5N/OM9ACA

[G8HVY]

Hi Bill
That is the G4FUF pre-amp kit which addresses the RX problem in more detail than the other pre-amp that you mentioned. There are good reports from many who use the kit there are more details on this link http://www.70mhz.org/847mods.htm
Don't forget the PA1O PA capacitor mod as this will reduce the 'I' drawn from your PSU. UK wersions of the FT-847 had an ALC clamping mod to reduce current consumption and clamp the output to 10w.Good luck Bill I hope to see you on 4 this season.

Graham.

[NZ5N]

Thank you, Graham. I have ordered Keith's kit. When it arrives and I open the radio, I'll probably do the PA1O capacitor mod to increase TX power, although I'm already getting 20 watts out and the maximum output in OM is only 10 watts.

The big problem, however, is that TX spur at 45.6 mhz. If I understand the PA1O TX mod correctly, I'd have to change out 10 components to resolve this problem, which may be beyond my technical skill level. I just don't know what to do about that.

We leave for Slovakia in 2 weeks and hope to be QRV from there by June 3.

73, Bill

[G8HVY]

Hi Bill
Yes you were right about all the component changes for the TX filter mod most of the surface mount devices can however be obtained from Farnell Electronics. You could however try this mod to remove the 45.6Mhz leakage http://www.70mhz.org/ft847_g7cnf2.htm
I have no personal experience with the mod however the author is a respected person within the 4m community.

73's

Graham.

[NZ5N]

Graham and all,

The preamp kit arrived yesterday from Keith, but unfortunately the construction appears to be well above my skill level. I do not have any experience working with such tiny SMDs.

So, if the unmodified FT-847 is as deaf on 70 mhz as most people say, I will not be able to activate Slovakia this summer as planned.

73, Bill NZ5N/OM9ACA

[MM0YET]

If it's any consolation, I agree with you.

I appear to have killed the FET while assembling my kit.

[CT1FFU]

For people that need a pre-amp on FT-847 and have no experience on electronics.
Click on link below.
That a ready build board, just need solder 3 wires, amd takes 5 minuts to do.

very simple and eficient.

http://cgi.ebay.co.uk/Yaesu-FT-847-Prea ... 483wt_1320

73
CU on 4m soon

[NZ5N]

I finally have the FT-847 up and running on 4m and have made my first 2 QSOs.

A local Slovak ham who is a technician for Motorola built the RX kit from Keith. It took him 5 hours, not an easy job.

He also removed C5050 for me. Easy to remove the capacitor, but an hour of work to open the rig and remove everything necessary to gain access to C5050.

He also did the G7CNF mod involving the addition of a 2.2nf capacitor to the left leg of L3024 for the purpose of killing the 45.6 mhz spur. This was easy to do but it did not work. It reduced the output on 70 mhz to just 3 watts.

So I am now QRV but still have some unfinished issues. After removing the 2.2nf cap, power output (without C5050) was 50 watts. In either case, I am not getting the 70-80 watts that the removal of C5050 is said to produce, not sure why. In light of Slovakia's 10 watt power limit, this is not a major problem, but I'd like to know why the mod did not have its full impact. Perhaps the rest of the power is going out on 45.6 mhz? I still need to do something about that spur.

Also noticed that, unlike on other bands, I am hearing my voice in the speaker when transmitting on 4m. This could be an antenna issue, but has anyone else noticed such a problem?

73, thanks for all the help, hope to work you on 4m this summer,
Bill NZ5N/OM9ACA

[NZ5N]

More troubles here. I was having such fun on 4m with my newly modded FT-847 that I did not check the other bands until late afternoon.

Unfortunately, there seem to be some bad side effects on 6m and 2m. When my FT-847 is set to SSB on 2 meters, I hear a buzzing sound, perhaps a chattering relay, as soon as I start to talk. The buzzing occurs only when talking on SSB on 2 meters. If the PTT is pressed but no modulation, then no buzz. And no buzzing on FM. And no buzzing on any mode on any other band. The problem occurs solely on 2 meter SSB. I do not see how the mod could have caused this, nothing was done on the 2m board, but it was working fine before.

Also, power output on 6 meters has dropped from 100 watts to 50 watts. This probably was caused by the mod, but I don't know why. Judging from earlier posts in this thread, it seems the new TX mod (the removal of capacitor C5050) was specifically developed to increase power on 4 meters with no effect on 6 meter power output.

Guess this is why many people have a different rig for each band.

73, Bill

[G0HOF]

Hello Bill,
It is dependant on what model FT847 you have got,is the CPU configered ok,has you place a ferrite core into L5006,it should be from Toko S102 VHF/UHF coil and stuck in place with a dab of mastic or glue,see G4FUF's article in the technical section of this site.A good friend of mine G4NVS done my 847 and I can get a good 50 watts out on 70 MHz and 95 watts out on 50 MHz. Alas poor Phil is no longer with us,he went silent key 3 years ago,he had a fully moded 847 and it a cracker of a radio on all bands,75 watts on 70 MHz.good luck with it if you follow G4FUF's article all will be fine.

Ken G0HOF

[IZ8DWF]

Hello all,

I recently modified my FT-847 with PA1O rx and tx filter mods. I made the TX filter as the UK version of course since mine was not originally an UK version.
I then removed the 390pF capacitor from the PA circuit, not the 470pF one as suggested by PA1O since others have suggested it has better performances on 50 MHz removing the 390pF instead.
On the RX side it seem to have gained about 10 dB (MDS was about -130 dBm on 70 MHz before the mod and about -140 dBm after).
I then had an almost full realignment session on the rig to the best of my test equipments (only old equipment anyway).
Here you can see the spectrum taken at 50 MHz cw 100W:

http://dl.dropbox.com/u/8652271/847out-50.jpg

You can see a rather broadband self-oscillation around 70-80 MHz, which is not good already.

On 70 MHz the situation is much worse:

http://dl.dropbox.com/u/8652271/847out-70.jpg

The 70-80 MHz self-oscillation is always there, I can't explain the two side bands at about +/- 3 MHz from the 70 MHz carrier.
Does anyone have a clue? I'm not sure where to check to solve the problem.
I'm also afraid that the capacitor removal causes some broadband instability (70-80 MHz broadband noise) and maybe goes unnoticed on others having made the same mod?

Best 73

Frank IZ8DWF

[GW8IZR]

Hi Frank - I modified two FT847's for people wanting to use them on 70MHz - I suggested that they take great care as the radio became very critical of the 13.8V dc supply, I certainly wasn't happy with the end result.

Anyway maybe what I noticed will help you locate the instability - a similar broadband noise that you report was seen under some supply voltages and power levels and you may want to look at the way the noise / stability changes as you vary the supply. (I did this with GPIB but twiddling the psu knob would do the same)

There were some unexpected changes in the efficiency on different frequencies. Using the radio to generate low tx power at 70.45MHz made the noise greater at 35-40MHz and much greater PSU current drawn. Running two tones at 10W PEP the noise was just 35db down, running 50W or so the noise wasn't easy to see, maybe 70db down.

Most people report that this modification works fine and only a small number of people seem to experience problems. OTOH if you don't look for problems... you won't see any. At least when you get to the bottom of the problem you will know the mod has worked for you.

GL

[IZ8DWF]

Hello Paul,

I should have also mentioned that the broadband noise is there as soon as you switch the PA in tx mode, there's no need to actually output a carrier to make it appear.
I have not tried anything else other than the old BIRD 82A as a load, I guess a not broadband termination would make the problem worse.
I've seen very few "modders" actually look at where the power actually is when speaking of FT-847. Most people are happy with the power meter alone.
Then I must be just unlucky of course.

Best 73
Frank IZ8DWF

[GW8IZR]

OK If its not drive dependant can you break into the drive and look at that? Also disconnect the drive and terminate the PA input with 50R and see what happens. I have seen broadband PA's benefit from just a db or so improvement to S11 so maybe a low value pad may tame the instability.