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Making Waves -Slow Scan TV

October 28, 2016 Leave a comment

One of the good things about the amateur radio hobby is its diversity.  If you begin to become bored with one particular activity there are always plenty of other things to try.  And so I decided to try something completely new (for me anyway) – HF Slow Scan Television or SSTV for short.

I downloaded the mmsstv software from http://hamsoft.ca/ and read through the instructions on setting up.  All very simple really, much like setting up JT65, RTTY or any other soundcard based system/software.  It does come with a few standard templates so I used these for a while until I got my head round the file size and clipping tools to create my own.

sstvscreen fig 1. My transmitted SSTV CQ message and control panel.

I have now made several contacts around Europe and Russia and the variety of images received is quite amazing.  Contrary to popular belief, they are not pictures of nakedness – they are images of nature, wildlife or screen grabs from cartoons.

sp5smy  fig2. Image received at M0CVO from SP5SMY.

 

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M0CVO Amateur Radio Antics The story continues..

Well, the TS-780 arrived, well packed in a Yaesu-Musen FT-221 box.  A really nice solid unit weighing in at a straight 10.1kg (22.2lb).  I took it out of the box and was pleased to see that it came with the 220v mains cable and not the 13.8VDC plug.  So I plugged it in and attached antennas to the two sockets on the rear of the case – a SO239 socket for the 145MHz antenna and a N socket for the 430MHz antenna. Plugged it in, turned it on and powered it up.  Well the lights came on but it was not showing the frequency on the front panel, nor were any of the other features operational.  Not wishing to panic I just left it for a while, still running and went to see if I could locate a full set of instructions and a service manual, yes, that’s right, there was none included with the radio.  I contacted Kenwood UK via their twitter account and Mark Haynes, M0DXR, the area sales manager, got back to me with both manuals that he e-mailed to me in PDF format.

CDwDWoAW8AA94Uv The TS-780 out of the box..

Returning to the radio I noted that it had fully come to life, displaying frequency correctly and being fully functional.  It isn’t a valved set but it still needed 5 minutes to warm up, it is an old set (1983) after all.  So I got my FT-232 handy (2m) and switched it to low power, set it on 145.425 and set the TS-780 to the same and tried them out both ways (1Watt only).  All working well.  Also tried the same on 70cm using my IC-E80 as the second set.  This working fine also.  I switched it to 144.300MHz, USB, and spent some time listening.  Obviously, on a Wednesday afternoon I wasn’t expecting to hear much but suddenly, out of the blue, a voice was heard, G4BZA was answering a call that I couldn’t hear.  Anyway, I followed them up to 144.305MHz and listened for a while.  Absolutely crystal clear RX and so much better sounding than on my modern FT-817, much less white noise.  I checked for distance and he is north of Horncastle in a village closer to Louth.  Not bad from my restricted location!  I also managed a short QSO with M1AIE/m on 2m FM but he was travelling away from me and lost me when he passed through Barkston Heath, a RAF base about 5 miles from here.

Then I started to source the issues with the radio.  The battery holder for the backup and memory storage was in pieces and crudely held with some cable ties.  Obviously this needed replacing as some of the contacts were missing.  This is to hold three AA batteries.  Secondly, the TX power couldn’t be increased on 2m above 1.5W so this needed looking into also.  The seller told me that on 70cm it was 5kHz out but on testing this it seemed alright so not an issue.

CD1UwiJWIAAmNhE Working happily on 70cm

So, day 2 and I opened the case up.  First thing I did was replace the battery holder.  Not difficult, just a five minute job.  Next task was to try and get the power levels up on 2m.  I consulted the manuals and checked the associated components leading up to the final PA.  All seemed fine so I assumed that the PA must be at fault.  the unit in question is 57713, a 144 -148MHz linear amplifier capable of giving 30W.  However, when I try to source them I discovered that they are no longer in production (what a surprise).  I contacted Kenwood again and they informed me that they had some left in Japan and gave me a number to call.  However, when I called, for a single unit it would cost me £88 with a 3 – 4 week wait for delivery.

CD1viamW0AAhLk_ Inside the beast

I recalled that the seller was also selling a 1kW linear for 2m and wondered if the owner of the TS-780 had adjusted the bias in any way to reduce the drive for this reason.  Back to the service manual and, leafing through the pages I noted that there was a way that this could be achieved.  Turning the unit upside down to access the final stages for 144MHz I located VR1, VR2 and VR3. Admittedly I needed a torch to see them crammed in at the back. Anyway, VR2 was bent towards the board showing that a screwdriver had been pushed in sometime.  Anyway, the voltage at L15 was less than the 0.5V that it should have been and the TX power was only 1.5W (CW).  I used a plastic hook to raise VR1 back up and then used a plastic trimming tool to rotate VR1 in a clockwise direction.  The power gradually came up and am now happy.  More tests will be undertaken in due course.

CD16bHTWAAAtYHt On 145MHz, TX.

M0CVO Amateur Radio Antics The story continues

You may recall that previously I spoke of a kit that arrived from China with no instructions and a parts list written mostly in Chinese.  This was for a 3.5W version of the 49er transceiver.

The receiver section was based around the NE602 AM receiver IC (8 pin DIL) with a 7.023MHz crystal to set the frequency and a diode ring as a demodulator (2 * 1N4148 diodes).  This then fed into an LM386 audio amplifier and associated circuitry.

TR switching is achieved by keying the buffer amp made up of Q2 (an 8050) and Q3 (an 8550).  This then provides a feedback loop through oscillator B and oscillator E through pin 7 and pin 8 on the NE602.  This then turns on Q6 (an 8050) to provide the base voltage for the final – a D882 NPN.  This then feeds into a band pass filter ( a pi filter made up of L4, 16 turns on a T37-2, C17 (470p) and C18 (470p)) and then to the antenna.

49er completed.

As can be seen from the image it is a rather crowded board.  I must now design a box for it as it is a little too large to fit inside my Altoids / Strong mints tin.  Will probably construct one from scrap copper clad PCB.

I have also found out that the TS-780 should arrive on Thursday so that will be something to look forward to as I test it out and refurbish it.

M0CVO Amateur Radio Antics

April 26, 2015 1 comment

It has been an interesting week for me.  I managed a 10 minute CW QSO with G1SCS on 40m, a mode that I am steadily improving at as I continue with my QSO365 challenge this year.  I have also started work on a kit that arrived from China with no instructions and just a schematic to work from.  This is going to be fun to work out.  Also this week I won a radio on a well known Internet auction site.  The radio is a Trio TS-780 dual band base multimode from 1983.  I do understand that the power is a bit low on 144MHz and on 430MHz it is 5kHz out.  Therefore this will become a project for me as when I was first licenced as M1DKN back in the 90’s, this was a dream radio that I could not have afforded (well over £1000 for a second hand one then).  I am just waiting on delivery now so I can make a start on it.

As to the kit it is for a 49er –  a 3.5Watt CW transceiver.  I have so far installed and tested the DC supply regulator – a 78L08 and associated capacitors plus the input / output sockets.  Next stage will be the RX once I work out what needs to go where.  I am enjoying doing it though and scratching my head at times.  I shall be happy when I am able to make my first QSO on it.

CDf0j2jXIAE0WIcThe 49er so far.

ts780The TS-780 dual band base transceiver