John, a friend of mine has recently asked me if I would take a listen for his 13cm (2.3GHz) narrowband transmissions which he hopes to have on the air soon.  When he asked me I had no suitable antennas in the air, but the dreaded cupboard contained a few relics from the days when I was an active TV'er on the band. Out popped a homebrew 15 ele loop yagi which was sadly past its best (see photo) and had a loop or two missing. After a clean-up it looked quite decent and I then spent a while re-attaching and straightening the elements. I also gave the reflector a new coat of Bacofoil. But there were a couple of small problems: 1. Where to site the antenna on the mast? It could have been squeezed in between one of the 70cm beams and the mast (see photo on first page), but this may have had detuning effects. 2. I didn't want the extra weight of another low-loss feeder, mainly because it's quite hard enough raising and lowering the mast at its present weight.
The obvious answer to both questions was to remove one of the beams and use its feeder. So down came the vertically-polarised beam and up went the little 13cm loop yagi.

While I'm waiting for John's signals to appear, I'm tuning around 2.3 - 2.4 Gigs and hearing a few signals. So far i've found an FM TV signal on 2415 MHz and some silent carriers around 2440 MHz. I'm using my AOR AR5000 receiver for this job, and I'm quite impressed. There's no mast-head pre-amp in the system and the CT100 feeder must be losing a significant amount of signal, but it works. More to follow, I hope.

I've always been fascinated by PLL etc, and when Huff and Puff first came along in the early 70's I decided to have a go. However due to other attractions (mainly beer and girls) I didn't tackle it until the mid 90's. The circuit I copied was a fairly complex one, but it operated in a manner that I could understand so I was able to debug it when it didn't work. After a bit of fiddling it worked well, with free 'knob' tuning and lock points every 64 Hz. Then I lost interest...

Then I stumbled across Han's Site (see links page) and started reading the Huff & Puff  reference library. Oh dear. Out came the HC CMOS box and a simple two-chip stabiliser was born. It uses a 4060 osc/divider to provide the reference signal and a74HC74 dual D-type for the detector/latch and the VFO. It refused to give a lock, and after a lot of hair-pulling I made one small change to the circuit which resulted in lovely clean locks every 1KHz.  One thing that surprised me was the amount of pull the 'varicap' LED gives!

Update: I got 50 Hz steps out of this simple circuit but it was a bit iffy, so I've moved on to a different design, also from Hans site. This is the 'Huff & Puff in practice' circuit by G3DXZ, and can be found at:

http://www.hanssummers.com/radio/huffpuff/library/ttsep96.pdf

Here's the veroboard version, which turned out to be too big to fit in my homebrew Topband rig. It's very simple - a reference oscillator (this one is on 27.277MHz), a HC4060 divider, a 74HC74 D-type, and a couple of transistors. 

The finished product. To save space, it's built  ugly-style on a plain copper board with a few 'lands' cut for the main connections. This one fits just nicely underneath the VFO. It works very well and I could sit and listen to its crystal-like note all day. Step size (at 2.4MHz VFO frequency) is 52 Hz - a 28.4 MHz ref osc would give 50Hz, but I didn't have one to hand. In operation it is almost invisible. When I sit down at the rig I press the 'setup' button, which sets the varicap voltage to half supply. After that it's just like normal - twiz the tuning knob to the required frequency and as soon as you stop twizzing the circuit pulls the VFO to the nearest 50Hz lock point, where it stays. The only odd thing about this arrangement (although it makes sense when you think about it) is that any attempt to tune very slowly results in a non-tuning VFO, as the huff & puff counteracts what it thinks is drift!

April 2007

Many moons ago, I was quite active on the Amateur TV side of things. I could transmit and receive video on 3cms (10GHz) and 13cms (2.3GHz) and had all manner of VCR's and tellies in my shack. But one by one my 'line of sight' paths became blocked by trees and buildings, until I had to give up 3cm. I carried on with 13cm though, using my little homebrew 20mW video transmitter to link to a friend across town. When he moved away, that came down too.

Away in the cupboard went all the gear. Some of it broke, some of it was given away and some of it just seemed to disappear. Then a friend of mine talked me into TV again.....

Out came the remains of the stuff, and this time I decided to build up a portable station that could be put in the back of the car for hilltop use. My little homebrew 900 to 1600MHz tuner (left, with its lid off) still worked, so all I needed to do was make a new 23cms antenna for it.

Here is the tuner all boxed up. The Amstrad tuner unit runs quite hot, but it doesn't seem to mind. The left hand knob is the main tuning, and the other tunes the sound from just below 6MHz to about 8MHz.

For receive on 13cm (2300MHz), I use an 'Arabsat' downconverter, which translates incoming S-band signals down into the 900 to 1700 MHz range which can then be tuned on the little receiver. The receive antenna for this band is a tiny 'bowtie' aerial (or bi-quad) which combines small size with reasonable gain.

Here are the guts of the qrp TV transmitter for 13cm after living at the top of the mast for a couple of years - a bit sad, but amazingly it still works and it's still on frequency!

And here it is back in its enclosure and on test. It's just a 'mimic' device configured as a 2340MHz oscillator and FM'ed by the video signal from the camera. Another - higher power - mimic amplifies the weedy signal up to slightly less weedy proportions.

A close up of the power-o-meter. A massive 22 milliwatts!  Ye gods, someone stop him before he kills us all!

Here's the 13cm loop yagi I've just built in an attempt to give the puny 20mW transmitter a chance. It's a length of plastic strip with a hole near one end to take the N-connector, which has the driven ele mounted directly on the top. The directors are loops of stiff copper wire glued in place, and the reflector is a square piece of aluminium sheet.

April 2007: I've decided to build another 'bowtie' antenna for the 13cms LNB, as the one I was using was a rather dilapidated specimen that fell out of the cupboard. Here it is during construction.

An in-line N-socket with a couple of inches of W103 coax fitted. This cable has a rather fat inner conductor that has to be filed down to fit the pin of a standard N. Note that I haven't fitted the nut...

..because the reflector is held on with it. All done up good & tight so nothing flaps about.

And here is the finished article after having the driven ele fitted. These antennas are very simple to manufacture and can be made quite tough. They're reasonably gainy too.

A woman's work is never done - that's why I shut myself in the shack and make things, away from the sound of the Hoover. Next on the list is a 23 cm TV transmitter

Here it is. It's built into a small tinplate box that I've been bursting to use for ages. It's an almost identical design to the 13cm one above and it behaves in the same way, which is always a good sign. An MSA0104 is the oscillator, and the amplifier is an MSA1105, capable of 60mW output.

Under test. The power meter is reading 30mW, so stand back! Just like the 13cm one, it's a free-running oscillator (no PLL or anything) so it drifts a bit. But it's fine for wideband FMTV.

May 2007: Here's the sound subcarrier block. The tin box contains the 6MHz oscillator, which is FM'd by the 3-stage mic amp on the veroboard. All I've got to do now is squeeze it into the TX control box.