Wednesday, December 28, 2011

Radio Communication Handbook

Gosh! I have wanted one of these for years, when I finally decided to get one for Christmas the other year it had gone out of print. Now I got one for this years Christmas present!

I have the older editions (two volumes) along with the VHF / UHF manual. They are excellent publications, but the projects in them are outdated. The latest edition is thoroughly up to date with the latest technology both digital and analogue. It has a nice balance, with some specialised projects using valves. The principles are still the same and it takes you back to basics. With all the digital technology in the world, you can't change the formulae of Ohm's Law, Resonant Circuits and Antenna principles. There are also a lot of useful and updated charts and graphs to explain things like radiation patterns and circuits.

I will always treasure this publication, certainly worth the £30!

50Mhz Halo Test

The final piece in the antenna jigsaw, putting up the 50mhz Halo.

When I sent for the antenna I wasn't sure just how big this antenna would look and also how it will perform. Assembling the halo was quite easy, but the instructions didn't mention how to tune this thing apart from the small variable capacitor on the connector block where the coax connects. The halo frame is adjustable and on the drawing it shows 4 inches as the extension length from the adjuster. The delta match is also variable in length, so after first assembling the unit I connected it to my FT817 to adjust for best vswr. After a lot of fiddling I got it down to 1:1. Now it was ready to fix up on the mast. The halo came with a good quality clamp and was easy to fix on the mast, but was very close to the satellite dish.

When I tested the halo on 50Mhz I was a bit disappointed. At first I couldn't hear the Buxton beacon, it is drowned by another carrier on top of it. Eventually, I managed to find it which although stronger than it is on the discone antenna, I would have thought it would come in stronger. When I transmitted on the halo the vswr went up very high, something is obviously wrong. I now need to get the ladders out again to maybe move the halo away from the satellite dish and re-tune the antenna.

I will reserve my judgement until later when I get chance to optomise the antenna and try it again.

Latest update - 28th December 2011

Today I took down the halo to make some adjustments and measuring. If you buy one of these from Moonraker (or anywhere else for that matter) the rather vague instructions that come with it are wrong! It shows a measurement for extending the square of the halo and shows it as 4 inches. The halo is tuned far too high in frequency and I found that I had to extend the square and delta match right to it's limits. Even at this, it tunes best at the top end of the band.
My halo is on a mast outside on the side of the house. I spent a long time at the top of a ladder fiddling with it and eventually giving up! After some thinking time it occured to me that a halo is of course just a 'bent' half-wave dipole, so I took a tape measure and measured the length excluding the insulated part. It turned out to be far too short for a half-wave at 50Mhz. I then adjusted the overall length to as near as I could get it. Even with everything set at it's extreme, it was still slightly short. After that I was able to tune the VSWR with the trimmer.

So now that I have the halo tuned I used the antenna during the 50Mhz contest to see how it performs now. VSWR is now down to 1.5 :1 and I must admit that every station I heard I managed to work even though conditions on the band were poor. It was a little anoying when other stations were using yagis and my halo is omni-directional. I would feel more in control to have some forward gain. I am also not happy with the position of the halo, it is screened in some directions because it is sandwiched between the houses. Would probably work better in the clear up on the chimney perhaps. I could hear the Buxton Beacon at s9, but I still think that it should come in louder than that. overall verdict on the 50Mhz Halo... It is adequate for general use on 50Mhz, but I would prefer a 2 ele HB9CV similar to my 70Mhz. I am limited for space though, so the Halo is a bit of a compomise.

Wednesday, December 21, 2011

Jean Genie Genius

I just watched a piece of television pop history tonight! Shown for the first time in 39 years!

David Bowie singing Jean Genie live on Top of the Pops back in January 1973 (a good year!) I find it difficult to believe that the BBC erased tapes of TOTP and other series after they had been shown! Maybe it was done to save money and re-use the tapes like we did with audio tapes. Well done John Henshall, the cameraman who saved hundreds of copies of stuff wiped from tapes.

"A retired cameraman has been speaking of the moment he realised he owned footage of David Bowie on Top of the Pops which was thought to be lost.
John Henshall, 69, from Stanford-in-the-Vale, Oxfordshire, retained a copy of Bowie performing Jean Genie in 1973.
He said: "I just couldn't believe that I was the only one with it. I just thought you wouldn't be mad enough to wipe a tape like that."

Mr Henshall said he only kept it because he wanted it for his showreel.
In the footage he used Telefex Fisheye lenses which he had designed himself. He also ended up in the background of one of the shots.
After the recording he asked producers for a personal copy on 2in (5cm) broadcast videotape.'Rarer than rare'
Mr Henshall said: "I didn't realise that it had been wiped by the BBC.
"They'd been looking for it for years, hoping that somebody had maybe pointed an 8mm home movie camera at the screen, because there was no VHS in those days. "

It amazes me how much television history has been 'wiped' over the years. On Monday I watched the film 'Hugo' which is a wonderful story of a movie-maker who destroys his celluloid films and finds them again by someone who saw the value of this analogue history.

Sunday, December 18, 2011

70Mhz receive converter

My versions of the converters. The top photo is the 50Mhz converter and the second one is the 70Mhz version. I currently use these as part of my transverters. I also made one for 144Mhz in a similar style. The 50 Mhz converter has a 3sk88 in the front end, while the 70Mhz uses 40673 mosfet. Note the different 28Mhz IF inductors, the 70Mhz uses a small torroid, while the 50Mhz uses a 1/4" coil former.

I ought to know the circuit of this converter by heart now, I have built so many of them for different frequencies.

My first attempts at a 144Mhz converter with an output frequency of 2 - 4Mhz (remember tuning high to low?) was not the best. It took ages to get things right with a FET front end and mixer. I could never seem to get it stable even after several rebuilds. Later, when I got the Yaesu FT101E I wanted to use this as a tunable IF of 28 - 30Mhz, so I decided on this design. It used two dual-gate MOSFETS, and also used feed-through decoupling capacitors and leadless discs. They were very easy to use and the circuit was very stable!

I first built a 144Mhz convertor which formed part of my transverter project, and then later built one for 70Mhz and also 50Mhz. All with the same layout, but different crystal and coils.

I still use all of these in my transverters, all are sensitive and stable

A great circuit, recommended for anyone wanting to build one of these as part of a project.

In the circuit I replaced the 3N140 with 40673 MOSFETS and then later used GASFETS like the 3SK88. My transverters for 144Mhz and 50Mhz have 3SK88's and for 70Mhz I used 40673's.

Monday, December 12, 2011

DF8QK 1296Mhz Transverter

Years ago I got hold of some partially completed DF8QK circuit boards. At first I built the 1296Mhz receive converter and after a lot of messing I finally heard a signal for the first time on the 23cm Amateur Band. Next I completed the three stage pre-amp and although quite noisy, managed to get it working as well.

This project took me ages to build and eventually I partially completed the transmit mixer. I assembled the units using copper clad board to make boxes for each unit with bnc sockets and plugs to connect between each unit. It was a bit of a nightmare to have, with wires everywhere!

The transmit mixer worked fine, but each time I wanted to use it I had to tweek some of the trimmers to make it work properly. I was truely amazed when I managed to work a station in France during excellent tropo conditions with just a few milliwatts of power!

Having worked a few stations on 23cm, my next project was to try to put all these units into a case and also build the power amplifier to give it some more power output.

For a while the transverter worked, but with a few problems with alignment that had to be constantly tweeked again. The big problem with the 23cm band is that nobody uses it unless there is a contest or tropo opening, so I never really new how well the transverter performed.

I still have the transverter, but it has not been powered up for years as I 'lost' the circuits and alignment details.

Last week I came across an old floder in my attic and guess what was in it? The circuits for the DF8QK! I was my task is to try to get this beast working again after so long. I don't know if it will be successful, but you can but try!

Sunday, December 04, 2011

Pye Bootmount Cambridge

About the same time as using the Pye Ranger on 70Mhz, I also had a mobile set up for 144Mhz. This consisted of a Pye Bootmount Cambridge complete with cables and A35 van to put it in. This was my first car! Originally the small dashmount control unit was mounted at the front and the main unit was on the floor in the back of the van. There were 6 crystal controlled channels and I used a home made 1/4 wave mag mount on 2m. (The magnet came from an old tv focus unit) At first I used it on AM, but later I fitted an FM discriminator (TBA120a) and modified the RF circuit to transmit in FM.

Later, I took the bold step of making the bootmount into a dashmount and building a front panel with all it's controls fitted to the side of the main unit. I then designed and built my fist ever digital LED digital readout that displayed the channel number (R6, S20, S21 etc...) It used a huge matrix of 1N914 diodes. It worked really well!

I used this set up for a while until I eventually bought a Sommercamp FM mobile at a rally. I still can't remember what I did with this Pye Bootmount Cambridge, I know that I also had a dashmout Pye Cambridge later. I think I must have taken it to a bring and buy stall at a rally.

Pye 70Mhz Ranger

After my last post I got to think about the old Pye Ranger that I used for a while to get me onto 70Mhz. I borrowed the rig from Neil G3ZPL, who used it himself for a while. This was a mean rig with a QQVO-320 valve in the final giving about 15 watts output. Although I called it a Pye Ranger, I don't think it actually had a name at that time.

Production life: 1949 - 1956

Standard frequency range: PTC114, 60 - 100 MHz,

Transmitter RF output: 10 -15 Watts AM

Primary model variants: 6, 12 or 24 Volt dc operation,

1 or 2 channel operation, PTC114Z-115Z later version using QQV03/20A PA valve.

I can't remember how I powered this rig, I think I must have wired this to a high voltage power supply. I remember using this AM rig to work cross-band with Neil G3ZPL.

Saturday, December 03, 2011

70Mhz antenna - HB9CV Review

At last! Some stations to work on 4m with my new HB9CV!
Last week was the Tuesday evening activity night contest on 70Mhz. These don't seem to happen every month, so I have had to wait for this one to come. I have always liked 4m, years ago I had a Pye Ranger AM set with it's all valve line up. I used this for quite a while until I built a 4m Transverter which I am still using now. I had lots of fun during VHF NFD back in 70's and 80' when I always opted to operate of 4m.

4m and 6m tranverter with the old Yaesu FT101E and HF Z-match. This is my present set up for 4m.
For a while I used a 2 element band 1 antenna which was fixed on the side of the house, eventually, it fell apart, so I was qrt on 4m for a long time.
I bought the HB9CV from Moonraker, which arrived after first being sent a 2m, 4 element instead of the 4m 2 element. This was then replaced with correct yagi but minus the extension rods required to tune the antenna. After an e-mail to Moonraker the rods were dispached separately. The antenna was easy to put together, but the instructions are not very clear, you have to work out yourself how to fix the driven element. Inside the the terminal box is an airspaced 'beehive trimmer' - not seen one of these for years! The trimmer is used to tune the antenna to obtain best SWR. This I found quite straight forward. This antenna has a rear mounting bracket, which is fine, but the supplied clamp was poor and even when fully tightened the antenna keeps dipping down. The extension rods have to be tightened with the screws fitted, I still don't understand why this kit has extension rods, why couldn't they make it all in one piece? You need lots of vaseline to keep the screws from rusting, they are stainless, but only coated.
The HB9CV is mounted on a rotator, so my first thing was to check the Buxton Beacon on 70.000Mhz. This was coming in well over s9, very strong!

On Tuesday conditions were poor, but I still managed to work 16 stations, my furthest being down in the midlands with just 5 watts. I like this antenna, it was quite sharp and had a good front to back ratio. I guess the HB9CV is actually a 3 element yagi with the driven element bent between the director and reflector. It is quite a neat antenna which doesn't take up much room, but performs we
It is a pity that 70Mhz is not used as much as it should, when conditions are good you can work long distances. I remember once working stations on cw during a good Aurora.

I found this design on the internet and used it to make a 432Mhz version of the HB9CV. Thank you to the German station that made the design. It works perfectly!
For 70Mhz just put in your own measurements (lambda is the wavelength of the band eg: 4 metres, 2 metres, 70 centimetres)