ft847 on 4 metres

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

FT847 Are newer examples better?

Postby G0AFH » Fri 15 Dec 2006, 17:23

Greetings All,

This is my first post on the 4m forum, so please excuse me if I am posting in the wrong place..

I have a FT847 purchased in late 2006. It has a 5J serial number. I have been toying with the idea of getting on 4m for a while now but having read about the problems with the 847 decided to wait until I had time to check the rig out properly.

Last night I ran the radio up on the bench. It produces about 10W for a supply current of around 15A. Looking on a spectrum analyser, the output looks relatively clean (compared to the pictures elsewhere on this site). It has two main sprogs approximately 3MHz either side of the carrier about 45dB down. The 45MHz LO is down in the noise.

Now for the questions.

Do later examples of 847 have better filtering?

Have I been lucky and got a better than average example?

Is the PA coil mod applicable to later radios?

Any comments gratefully received

73
Ian
G0AFH.
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New pre-amp board from G4FUF

Postby G6GVI » Mon 8 Jan 2007, 18:56

I've just heard from Keith G4FUF that the long-awaited pre-amp boards are now available. Full details can be found in section 4 of the page:
http://www.70mhz.org/847mods.htm
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Postby G6GVI » Wed 10 Jan 2007, 17:25

Keith has added a picture of his little pre-amp board fitted inside the radio:
http://www.70mhz.org/847mods.htm
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Postby G6GVI » Tue 16 Jan 2007, 23:27

Subsidiary topic started by Gary re overheating of modified 847 on 4m FM:
http://www.70mhz.org/forum/viewtopic.php?t=1001
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Postby G6GVI » Sat 10 Feb 2007, 15:45

Keith has added another ordering option to his pre-amp kit: PCB and connectors only for £19.50.
He is also developing a switched transmit band-pass filter kit for non-C2 models.

These details have been added to the original article:
http://www.70mhz.org/847mods.htm
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Postby G5WQ » Mon 9 Jul 2007, 17:00

hi all ;

i have just got an FT847 serial number 8H .

seems someone put a ferrite slug in the L3005 core but i have changed it to a 2 dot toko one anyway .

in mine i have a small transistor soldered directly to the pcb board on the AF/CTRL unit with one wire [green] which goes around other side of radio , presumably to rf unit [i havent checked that close just yet ] .

is it this wire that you cut to enable 4m to produce "full" output .

currently i have 10w output for about 12amps current draw .

tcvr is a C2 version and correct logic jumper configuration .

it has not been widebanded on HF 0-30mhz at present , if i did do this though would it affect 70mhz operation or do i need to wideband it to enable 70mhz full output etc .

thanks
ian G5WQ
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FT847 filter modifications from Marc PA1O

Postby G6GVI » Sun 12 Aug 2007, 14:50

Marc has produced two documents, covering his analysis and simulation of the RX and TX band-pass filters, and the PA output and low-pass filter circuits.

His analysis highlights errors in some of the previously published component values, and suggests corrected values.
Marc's documents also include photographs of the PCB modifications, and his measurements of efficiency and reflection coefficient.

His documents can be accessed from the Technical Features section:
http://www.70mhz.org/ft847_pa1o.htm
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Postby G6GVI » Sun 19 Aug 2007, 07:30

Message from Peter G8BCG:
Congratulations to Marc PA1O for his detailed analysis of the 847 low efficiency / low output issues for the 847. I had already tried the ferrite core mod but only got to 20w on my UK 847. I was impressed by Marcs article so decided to have a go. 20minutes later and I now have 60w of clean 70MHz with high efficiency (after remembering to disable to UK power limiting wire - see previous notes).
RECOMMENDED TO ALL - MANY THANKS MARC 73 Peter G8BCG
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PA1O's FT 847 mods

Postby G2AXQ » Sun 21 Oct 2007, 17:11

Hi Ross,is it possible for your friend Peter to supply any information on the inductances that he changed and where he obtained replacements.
I also have done the "core in the coil" mod but without much success.
Many thanks
John G2AXQ
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Postby G6GVI » Mon 22 Oct 2007, 11:13

John, you can contact Peter directly using the "pm" (private message) button. Just enter "g8bcg" into the Callsign window.
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Postby G0EHV » Mon 5 Nov 2007, 12:51

Hi,
Having done the "Inductor" mod on my 847 with limited success - best output on 70Mhz of 50W with 20A current drawn but still highish current at lower power levels, I was interested in the PA1O mods.

Left the inductor mod in place and removed C5051 as Marc recommended produced an unexpected result. The effciency at lower power output improved but the maximum output power was down to 21W with 10A of current.

Removing the inductor mod did the business - Power max of 55W with only 13A current drawn and much better eficiency at lower output levels. For example running 20W draws only 8A.

The effect on 50MHz is also measurable. Power max is down slightly at 95W with 18A drawn. With the inductor mod it was 100W with 24A drawn.

In summary, a useful mod but worth documenting before and after power/current measurements at various outputs.

Once again, many thanks to Marc (PA1O) for the original excellent article.

Regards,
Eddie
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Postby PA1O » Sun 27 Jan 2008, 15:30

Hi all,

After my article on C5051 I opened the set again
to optimize L5006 just to find that the original value worked
best for me. The PA gain at 6m is (only) just sufficient, maybe
replacing C5051 with something like 100 pF would be a better
compromise and give 100W at 6m for everybody again at slightly higher current (and lower power at 4m)... Anyway, I'm happy with the present
performance.

So for max gain at 70 MHz indeed keep using the original value for L5006 as you already found out.

It should be possible to get 100W at 70 MHz with <23A current, but we are still lacking gain in the driver stage. Does anybody feel challenged? I'm rebuilding my shack at the moment, so I have no time to try and optimise further...

73 de Marc PA1O
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G4FUF mod completed

Postby M0BPQ » Fri 4 Apr 2008, 15:06

Hi Folks,

Just to add to the body of evidence.

I have added both a G4FUF preamp board and done the slug mod to my 8G UK model FT-847 today. Like G5WQ's model mine has a discrete transistor stuck to the board for the ALC power reduction. The preamp is a big improvement over my previous external one and is obviously much neater. I installed a core (obtained from the same source as EI2IP - thanks for the tip) with approx 1.5m protruding from each end of the coil. Whilst the 50MHz side draws about 2A more, it still produces 100W output. On 4m, I get about 60W out at 20A. During key down for 1 minute there is a downward drift to about 55W. The modified coil gets no warmer than any other parts of the PA board.

Many thanks to G4FUF for his hard work and for the lively discussion on the forum. I don't have the kit to check spectral purity at 70MHz.
73
Steve
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Great PA1O !!

Postby IK0YYY » Thu 8 May 2008, 10:36

Rome, May 8, 2008


Hi all,

I would like to tell thank you to Mark PA1O, for his modification about RX and TX filter on Yaesu FT847.

I have made this modification and the result is excellent !

First, I have made the modification of G4FUF and I found:

- -112 dBm on RX sens. for 12 dB SINAD;
- 9 Watt on TX;
- 21 Ampere on TX;
- terrible spectrum view ......

Note: the modification on L5006 no change the power output !!

Then, I have read the sperimental work of Mark, on RX and TX filter, and I have tested it, with these results:

- -121 dBm for 12 dB SINAD;
- 9 Watt on TX;
- 5 Ampere on TX (at 9 watt);
- optimal lines on spectrum at 70 Mhz !

For the power, I have found in my equipment, the "extra" transistor and I have cut it. now, I have 68 Watt at 19 Ampere. The spectrum view is ok !!

Thank you to www.70mhz.org, to G4FUF and to PA1O.

Luca Ferrara, IK0YYY, Rome, Italy.
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Postby G0KSC » Sun 29 Jun 2008, 10:27

pa1o wrote:Hi all,

After my article on C5051 I opened the set again
to optimize L5006 just to find that the original value worked
best for me. The PA gain at 6m is (only) just sufficient, maybe
replacing C5051 with something like 100 pF would be a better
compromise and give 100W at 6m for everybody again at slightly higher current (and lower power at 4m)... Anyway, I'm happy with the present
performance.

So for max gain at 70 MHz indeed keep using the original value for L5006 as you already found out.

It should be possible to get 100W at 70 MHz with <23A current, but we are still lacking gain in the driver stage. Does anybody feel challenged? I'm rebuilding my shack at the moment, so I have no time to try and optimise further...

73 de Marc PA1O


I have been 'working on my FT847 for a few months with many different cores in trying ot get a resonable output. My latest resulted in 60 watts at 23 amps. Not ideal. Reading the notes on this site again, I found this thread and PA1O's capacitor removal mod. I had nothing to lose so I removed the PA today to try it. At the same time, I removed the core I had placed in the coil. 17.1 amps for 93 watts on 6mtrs and 16.1 amps for 82 watts on 4 mtrs. Incredible. Thanks for the info and research!

Justin G0KSC
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