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Saturday, 28 May 2016

DX TV signals from Poland

The Sporadic E season is well and truly "happening" with an opening to Scandinavia on the 25th, when I worked SM5ZCJ, OZ2KEC and 9A2RD all on 6m. The next day it was even better, and I worked SM6CXS, YL2SW, ES5QD, LA5YJ and YL2GP. On this day I heard 2M0UAL working another UK station, this Scot was only 520 miles, much less than the usual 1000 miles. A shortening skip distance often indicates that higher bands are open too and Facebook posts on the 70MHz group confirmed that that band had been busy too.

Last night was fairly quiet, although I did work EA7JUR (and his pet cat).

Well today, it has been Poland coming through loud and clear. I worked Roman SP9RM and Bogdan SP4LVC. While I was waiting for my chance to work Bogdan, I noticed that there was a buzzing sound, which is TV frame buzz. It is quite distinctive because the sound of the buzz changes each time the camera angle changes. So I quickly got out my 5" black and white portable TV set and connected the 6m antenna to it.

I was quickly rewarded with, first synchronisation bars, and then, pictures. Well they are pretty grainy, but at times they were clear and watchable.

I also tried to make a little video to show how the pictures were constantly fading in and out. I put that up on Youtube, here.

Unfortunately, in Europe, the TV frame rate is 25 frames per second, which doesn't work at all well with the 30fps frame rate of the camera. The result is an unstable image with black bars which weren't on the original... but it kind of gives the idea.

For the record, my antenna is very simple, just a 1/4 wave ground plane - that's a 1.5m long whip, poked through a hole in the ridge of the roof. The felt underneath the tiles has an aluminium foil covering, and that is connected to the shield on the coax, so the whole roof becomes a ground plane.


Wednesday, 18 May 2016

External Speakers on FT847

When operating a special event station it is useful if the visitors can hear the audio output of the radio, and it is also useful if the operator can wear headphones - because there is always chatter and other noise going on in these places. But, when you plug headphones into the Yeasu FT847 the loudspeaker is switched off, so no one else can hear.

I found a fairly easy way round this. There is a second audio output available on the rear of the radio which has a 200mV output level, that is independent of the Volume control on the front panel. This is on a stereo 3.5mm jack socket marked Data In/Out. It is intended for connecting a packet TNC, or other data-mode device to the radio, but the audio quality from this socket is good.
Red arrow shows the Data In/Out connector on the back of the radio.

 The output is about the right level to drive a pair of PC speakers, but there is a snag ... The audio out is on the ring of the jack and the tip is used for PTT and for audio in, so if you plug the stereo plug from the speakers into this socket the radio goes straight into TRANSMIT! This is because the input impedance of the speakers is sufficiently low to make the radio think that the "TNC" has selected transmit. So I made up a simple adaptor out of a plug and socket, wired as shown below ...
Do test the speakers with the radio on transmit before using them at the event, because PC speakers are notorious for being sensitive to RF fields and may demodulate your SSB transmissions in an unpleasant way! Fortunately the speakers lent to us by Chris, G6AFY, were of high quality and behaved very well.
So here is a picture of me operating GB8WW with my FT847 and the PC speakers plugged in the back, the stylish, wedge-shaped thing in the foreground. If you look carefully you can see the adaptor-lead plugged into the back of the radio.

The headphone volume is controlled by the AF gain control on the front of the rig and the PC speakers are controlled with their own volume control.

One of the criticisms of the FT847 is the "steppy" digital AF gain control on the rig, making it hard to get the right listening level - so using an external speaker on this audio output might be a way round this in the shack - so this adaptor might be useful for more than the occasional special event station.

Happy Operating, and 73
Hugh M0WYE

Monday, 2 May 2016

Headset adaptor for FT847

It is nice to have both hands free when using the Amateur Radio - especially when operating a Special Event station or contesting, because you can fill in the log, and fiddle with the radio controls while talking. And  ... your thumb gets tired using a fist mic!

With the popularity of gaming and Skype, some nice headphones with microphone booms are available quite cheaply. I bought one of these: "Gearhead" AU3700S Computer headsets for £10.91. This one has 3.5mm stereo jack plugs for the microphone and headphones. I noticed that quite a lot of the headsets now come with a USB plug, which presumably has a USB soundcard built in. Not much use if you want to connect to an old analogue wireless set! Make sure you get one with jacks.

The headset is actually terminated in a "four ring" jack plug, suitable for Apple devices (apparently) but comes with a Y adaptor with a separate plug for headphones and microphone.

To use the headset with a radio we need some kind of adaptor box. This will have socket(s) for the headset and leads to plug into the microphone and headphone sockets on the radio. It will have a Transmit/Receive switch or PTT button, and with supply a bias Voltage to drive the electret condensor element in the microphone.

So this is what I built. I decided to stick with the "Y" adaptor on the headset, because it means that the box becomes more versatile having separate sockets for mic and headphones. I wanted the box to be well screened because there maybe high RF fields around, so I used a diecast aluminium box, from Hammond Manufacturing (Pt. No. 27969PSLA) - it is one I picked up last year at a Radio Rally. I found some flexible 9-way screened cable - more conductors than needed but I doubled up the ground connections to try and keep the impedances low.

But we have to be careful not to introduce ground loops. There is the cable screen, there is the microphone ground, there is the headphone ground and there is the PTT ground, and really they should all be kept separate. Trouble is a lot of jack sockets have a metal fixing nut that connects the barrel of the jack to the metal box that they are mounted on.
Fortunately I found some inexpensive, 3.5mm Jack sockets on E-bay which have a single (8mm dia) hole fixing, but are completely insulated from the metal panel.

Gold-plated too!

The FT847 manual has a useful diagram showing the microphone connections. The headset connections are fairly standard - in fact there is an industry standard which specifies the microphone and speaker connections. On the microphone the tip carries the signal and should be capacitively coupled, the ring carries the bias Voltage which must be less than 5.5Volts and sourced from an impedance greater than 2.2 kilohms. I used a 10uF solid aluminium electrolytic capacitor and a 3k9 resistor for coupling and bias resistor. Seems to work well.
Here is a circuit - drawn on CAD as you can see :-)
The mic connector is viewed looking at the front-panel of the radio. So it is viewed from the solder-terminal side of the (female) microphone plug.

The "spare" pins on the mic connector are used for "up" and "down" buttons on the microphone - but I haven't used them here.

The headphone circuit is kept completely separate - partly because the radio offers the facility to listen to your own SSB transmissions, so we don't want any audio getting back into the microphone socket. I used RG58 for the interconnecting cable, as we only need a mono signal for the 'phones.

the TX/RX switch is just a bog-standard DPDT toggle switch.

So here are a couple of pictures of the "innerds".
 I have tywrapped the incoming cables to the body of the jack socket. There may be more elegant ways of strain-relieving the cable but this seems to work ok.
The big fat grey wire, is actually the braid from the multicore cable being soldered to a solder tag on the die-cast box. Might have been better if this was a shorter connection from an RF screening point of view, but hopefully it will keep HF frequencies out of the box.

The finished box looks like this:

On air reports have, so far, been favourable. One thing to note is that the output of the electret condensor mic is much higher than the standard fist mic supplied with the radio. I used a deviation meter to check the FM modulation level, and found that I had to reduce the FM microphone gain from 32 to 12 in the menu system. Menu 25 [FM-PSET]. I also went through the procedure for setting the SSB microphone gain - setting the meter on the rig to measure ALC using Menu 24 [TX-MTR]. Strangely the SSB mic gain is set close to where it usually is. The "Moni" feature on the radio is great for listening to your own input, you can set the Monitor Volume using menu 20 [MONI-VOL] - but unfortunately you can't monitor when using the speech processor as it uses the same circuitry!

So there you have it, a Bank-holiday-Monday headset to FT847 adaptor box.
Hugh M0WYE

Further notes

The 3.5mm Jack is an EST Part: Part no. MJ073H, from Ebay, here

8 pin microphone connector also from Ebay:
But found the thread on the locking ring was poorly made, and won't screw up on the socket - so I will have to change it ... a pigging nuisance!

Wider transmit range on FT847

Some years ago UK Radio Amateurs were permitted to use the upper part of the 40m band, 7.100 - 7.200MHz. Many older radios, sold in the UK, such as my FT847, restrict the transmit range to what was previously legal, 7.000 - 7.100 MHz. It is rather frustrating when you can hear QSOs or CQ calls, but when you press the transmit switch you get a "beep" and an error message. Doubly frustrating when you know the circuitry is quite capable to transmitting and radios sold in some territories, such as the USA, do cover that part of the band.

I wanted to use the radio during the forthcoming "Mills on the Air" special event station, GB8WW, and it seems that the 40m band is used a lot for Special Events, so full coverage would be essential.

"Widebanding" radios, modifying them to transmit at any frequency, is quite commonplace, but requires the operator to take great care not to transmit outside of the band where they are legally allowed to. With the FT847 there is a further complication. The radio covers VHF and UHF as well, and the programming links which set the TX limits also affect the repeater shifts and the radio's ability to transmit on the 70MHz VHF band.

Fortunately G1IVG has put a useful table on his website, here, which shows the different ranges available. The programming links are on the PCB next to the memory backup cell. You can see them, numbered from 1 to 6 in this picture.
 The links look like surface-mount resistors, but are actually "zero-ohm links", and can be replaced by blobs of solder or very short pieces of wire. You can see that links 1, 2, 5 and 6 are shorted and links 3 and 4 are open. (Always useful to take a photo before you make a modification so you have half a chance of putting it right if it doesn't work!).

Looking at G1IVG's table you can see that there are only two link settings where the radio has the 70MHz band, the first is the standard UK configuation that I have, and the second one has links 1,2 and 6 shorted and the others open.  The HF options are in the table below, and this link combination gives the HF bands in row 5.











All the HF bands, except topband and 10m, are made 500kHz wide - so one still has to be careful not to transmit out of band, but, the problem of the 40m band is certainly solved by this. It doesn't allow the radio to operate on the 60m band, but (at the moment) this doesn't interest me much.

The 2m and 70cm bands become very wide, 140 to 154 and 420 to 450 Mhz respectively, so again, some care will be needed when operating on VHF too.

Performing this mod wipes all the channel memories and any changes you may have made in the menu system (display brightness, channel steps etc.), I already had a list of all my channels, with the CTCSS frequencies, repeater offsets etc, but I went through the menu system and carefully recorded all the settings there too.

So... I chose the finest soldering iron bit, found my tweezers and strongest reading-glasses, and set to work. Instead of removing the link 5 completely, I turned it round, so that it is still attached to the ground pad. That makes it easier to undo the mod, or reuse the link on a different pad if I need to.

The photo at left shows link 5 under a magnifier.

The links are only read by the microprocessor at factory reset, so it is necessary to hold down the "lock" and "fast" keys when you power up the radio for the mod to take effect. This is why all the all the channel memories are erased.

I turned the power control down to minimum, attached dummy loads to all four antenna sockets and carefully explored the frequency ranges. I am pleased to report that the new transmit ranges seem to match up with those in the table.

The repeater offsets basically match up with the UK standard settings, except for 50MHz where the offset is 1MHz instead of 500kHz. This is configurable in the menu system. So it all seems quite promising, and the radio is "good to go" for Mills on the Air 2016.

Hugh M0WYE