My FT847s got no nose...

So how does it smell?

Like an electrical burning.....

This morning in a state of sleepiness I agreed a 4M Meteor Scat sked with a European station. I started to TX on the 2nd half of each minute. After wondering why the power out was so low for a while I realised that I hadn't got an antenna connected! By this time small whiffs of the magic smoke were emanating from the back of the radio.

I've done some tests now the smoke has cleared and I have RF out on HF, 2M and 70cm so I conclude that the PA must still be intact. I don't have any RF out on 4 or 6M however.

There's a low pass filter (LPF) for those two bands and I suspect the smoke may be from the components in that filter somewhere. I've had a look at the top side and the inductors in the filter look intact, the damage must therefore be on the underside of the PA board. I've had that board out before when I did the PA mod for 4M, and it's quite tricky as you have to remove the PA transistors from their heatsyncs.

As I am going to A71 land again on Monday - I'll take this to have it looked at - with a bit of luck it'll be fixed before I get back.

Cat agrees with my diagnosis:

Muppetry, egh?

Where do the knots come from?

Well,

I've been checking some wiring today; there's a great deal of it in my shack and it's always in a spectacular knot!

I saw some SWR movement during the XE contest at the weekend and thought it was worth investigating... as normal I have found a PL-259 connector soldered in the most appalling way possible - I suspect this may be the culprit so it has been duly replaced.

Whilst I was doing this I decided to draw a diagram of what is connected to what -  was getting in a bit of a muddle, so here it is:

So at least I have a known reference point to look back at now.

Not very exiting, is it?

FT-847 PA Mod - there's a better way!

Well,

Following the mod of the PA filter in my FT-847 here:

http://g0mgx.blogspot.co.uk/2012/06/ft-847-that-i-have-here-includes-70mhz.html

I've been thinking some more about this; given that the PA is capable of delivering 100W on 6M or 50MHz, it wasn't clear to me why I Was struggling to get more than about 60W out on 4M or 70MHz. There had to be some very large inefficiencies in there; then I discovered this link:

http://www.70mhz.org/847filters2.pdf

And all became very clear, very quickly! I don't know what package Marc used, but he has done a fine job. Once again the FT-847 came apart and I kept removing bits until I had discovered the PA board:

Now, to make the mod described by PA1O, Marc, I need to lift the PA board out. This was a bit scary as I had to remove all the screws holding the MOSFETs onto the heatsync and then very gently flip the board over. Once upside down, I could clearly see the two caps described in the article:

Then with rather a lot of brute force and ignorance I managed to get the one cap removed; it's been stuck down rather firmly so it kind of came off in bits with no hope of ever putting it back again!

So, after carefully putting it all back together (including a dab or two of heatsync compound), the radio is back together. I've removed the ferrite I added when I did the previous mod:

http://g0mgx.blogspot.co.uk/2012/06/ft-847-that-i-have-here-includes-70mhz.html

And I now have a full 85 - 90 Watts out on 70MHz with about 16A current draw and still have 100W output n 50MHz with a reduced current draw of 17A (it was about 21A); so I think we can conclude that efficiency is improved.

I can't see any negative side effects of this modification to the PA, the output seems stable on all bands but I'll be sure to let you know if I find out differently.

I'm going to look at the output spectra a some point in the near future to make sure the signal is nice and clean and all harmonics are suitable suppressed.

Cat's not impressed:

Good though, egh?

FT-847 Pre-Amp Installation

So, now that I have built and done the basic DC test on the new FT-847 pre-amp last time:

http://g0mgx.blogspot.co.uk/2012/06/ft-847-4m-70mhz-pre-amp-mod.html

It's time to install the board in the Radio. This looks to be a fairly straightforward operation, replacing one board for another.

Here is the old "daughter" board inside the radio just prior to removal:

And this is the gap - this picture was taken to ensure I could remember where the old board wired into the main board - re-fitting being the reverse of removal!

So here is the new daughter board which includes the 70MHz pre-amp just being tacked into place:

And here with the wiring complete:

All I need to do now is find a suitable signal and peak the variable inductor for maximum smoke; that should be a doddle. I can hear the relays operating as the tuning range enters and leaves the operating frequencies, so something is working as planned.

Not bad, egh?

FT-847 4M (70MHz) Pre-Amp Mod

As I mentioned in my last post here:

http://g0mgx.blogspot.co.uk/2012/06/4m-70mhz-and-counting.html

I had bought a mod for the FT-847 to improve the reception on 4M (70MHz). The kit is made by G4FUF and is really quite a neat package which you start with the surface mount components:

Once all the SMD parts are on the board there are a number of inductors:

followed by a pair of relays and an rf connection or two:

So next is to perform a basic DC test and then install inside the FT-847...

Watch this space!

4m (70MHz) and Counting....

Following on from the mods I undertook on my FT-847 here:
http://g0mgx.blogspot.co.uk/2012/06/ft-847-that-i-have-here-includes-70mhz.html

I've bought and put up a 4M beam. I've not got it so it can be rotated, nor is it very high off the ground, but it's pointing to the SE and ready for those Es!

So, the house looks like this from the side:

So here you can see a 6M, 2M and now a 4M beam, a vertical for 2M, 70cm and 6M plus the centre of the Windom. The main HF antenna is on the back of the house.

My next project will be a 4M pre-amp for the FT-847 which I have already bought as a kit:

This kit is from Keith, G4FUF, he seems to be the font of all knowledge on the FT-847 and converting it for 4M. I'll post more about this when I make the kit and install it in the radio.

I've also started to think about WSPR on 4M and have just built a 60MHz local oscillator which I could use to mix with a 10MHz signal to get onto 70MHz. All just thoughts at the moment:

Cats not been helping much, as usual:

All good fun though, egh?

FT-847 on 4M or 70MHz

The FT-847 that I have here includes the 70MHz band when you sequence through using the band up and down button; it also excludes the more recently allocated 7.1MHz to 7.2MHz at the top end of 40M. The latter doesn't bother me too much.

The RF out on 70MHz is a mere 10W, and I have recently been reading about a mod to increase this safely.

The details of the mod have been published by G4FUF here:

http://www.70mhz.org/847mods.htm

The first step is to remove the outer casing by taking off the carry handle and other associated screws, then we need to confirm a number of jumper settings and then measure some test points:

this is to confirm that the on-board configuration is as it needs to be. The test points are in this area of the upper board:

Then the lower board needs to be moved out of the way, this is a simple task by removing 4 gold screws and flipping the board towards the front of the radio:

This provides access to the PA, but first the shield has to be removed:

 Then, finally, we have access to the PA:

Then a piece of ferrite needs introducing into the centre of L5006; this will bring the resonance down to below the 70MHz band.

****** IMPORTANT ******

It is essential that the correct type of core is used otherwise excessive heating may occur; you cant just use any piece of ferrite! The core needs to have a relatively low mu and should be a VHF/UHF type. The core from a TOKO S18, MC120 or MC122 are usable and are currently available from JabDog:
www.jabdog.com


****** EVEN MORE IMPORTANT *******

There's a better way:

http://g0mgx.blogspot.co.uk/2012/06/ft-847-pa-mod-theres-better-way.html

*************************


You can see the modified component right in the centre of the photo here:

Once this is complete, it will have initially made no difference at all!
We also need to remove the ALC mod that is still restricting the output on 70MHz, this is completed by snipping the green wire in the image below (this is the top board in the radio):

Now I have the desired 65W (ish) out on 70MHz. I've ordered a pre-amp kit to improve the radio on RX, I'll post more when it arrives.

Good though, egh?