Modifications for Amateur Radio equipment...

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Modifications for Amateur Radio equipment...

Post  G7VGG on Mon May 04, 2009 7:27 pm

If you know of any good mods for any of your Amateur Radio equipment please feel free to post them here, but please take note that I will not accept any responsibilty for any possible damage that may occur by performing these mods.
Personally, I will only post mods here that I have successfully performed on my own Radio equipment and therefore are mods that I know to work first hand and that make big improvements in either the reliabilty and/or usabilty of my equipment.
73
Alf (G7VGG)


Last edited by Admin on Mon May 04, 2009 7:42 pm; edited 1 time in total
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The PA10 4m band PA improvement mod for the UK spec Yaesu FT-847

Post  G7VGG on Mon May 04, 2009 7:35 pm

In standard UK spec the FT-847 gives out just 10 watts on 4m but at a rediculously heavy power consumption of around 20 amps. Clearly a lot more RF is being generated than is being radiated due to very poor filtering of the 6m IF and therefore the PA is actually amplifying numerous spurii on either side of the desired frequency with some of the spurii at around 45MHZ being only a couple of DB down on the strength on the desired frequency on 4m!!!
This manifests itself as the radio getting very hot when you have qso with long overs on 4m.
Fortunately there is an extremely simple mod that can be done to the UK spec Yaesu FT-847 that addresses the very poor 4m PA performance.
The mod was discovered by Dutch Ham, and electronics genious, Marc Vlemmings (PA10) and it basically involves removing a single 470pf SMD capacitor (C5051) and then snipping one little wire on the other side of the radio (that goes to the ALC transistor)...and thats about it!...Well there is actually one difficult bit...You have to dissasemble a lot of the FT-847 to get to the capacitor in question, but as long as you make notes on paper of which screws and panels go where as you go it should'nt take more than half an hour or so to do.
The results are a maximum output of around 85 watts on 4m but at a much reduced power consumption of around 16Amps AND the power consumption at 100 watts on 6m also goes down from 21Amps to around 17Amps at the same time! The PA efficency on 6m and 4m is therefore greatly improved, you get a lot more power to play with and the FT-847 no longer gets hot when you have a QSO with a few long overs on 4m. Very Happy
If you are interested and want more info see here for more info on the mod and a few others that Marc came up with, click the following link:
http://www.vlemmings.com/PA1O
73
Alf (G7VGG)
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The DL8UA powerswitch mod for the Yaesu FT-847...

Post  G7VGG on Thu May 07, 2009 7:11 am

This mod was designed to address the problem of prematurely failing FT-847 powerswitches. Apparently the powerswitch contacts on the FT-847 are only rated at somewhere between 250-500mA, yet they are forced to handle a current of about 1 Amp every time the powerswitch is used...The result is a tendancy for the switch contacts to burn out. A new FT-847 powerswitch is'nt cheap and replacements may even become totally unavailable as production of FT-847 was stopped about five years ago.
Fortunately there are a couple of solutions:
1) Bypass the powerswitch contacts with a small relay, or...
2) Bypass the powerswitch contacts with a P Channel MOSFET.
The first option is the cheapest solution, with a suitable relay available from Maplins for less than £1.50, but it draws around 350mA to energise the relay coil/s and you get an annoying click from the relay everytime you switch the FT-847 on.
The second option is still cheap (compared to the price of a new FT-847 powerswitch) but it costs about a couple of pounds more to impliment than the first option as you need two additional electronic components in addition to the MOSFET itself. However is has two advantages over using a relay:
1) It only draws about 170mA everytime you switch the FT-847 on, and...
2) Its completely silent.
The second option was discovered by German Ham Dirk Schray (DL8UA). If you are interested in performing this mod on your FT-847 as a preventative measure, you will find the details of the mod about half way down the following webpage you come to after clicking the link below:

http://www.schray.de/847/index.htm
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