Hello and welcome to my web site.
I obtained my AOLCP and first licence (VK5ZIJ) back in August 1969. Since then, various things have interrupted
the hobby (marriage, work, kids, etc.) with the result that there have been rather large gaps in my activity.
Currently, my main interest lies in experimenting with equipment for the microwave bands (1296MHz - 24GHz). I
have constructed transverters for 23cm, 13cm, 9cm, 6cm and 3cm.
73
Iain
Page Last Updated: 9 April 2010
12831 Visitors since 9/08/2009
| 14 May 2010 | I've been doing some more experiments with WBFM on 10GHz. The traditional method for doing this is to use a Gunn oscillator/detector. While these work OK, they suffer from some of disadvantages:
(1) Poor frequency stability.
(2) Poor receiver sensitivity.
(3) The other station must transmit on a different frequency (difference being the chosen I.F.).
I then tried a 'motion detector' module that used a DRO. This was much more stable than the Gunn oscillator but difficult to modulate since it's almost immune to variations in the supply voltage. I finally settled on a system that multiplies up from 70cm. The output from my FT-60 hand-held is fed (via an attenuator) to a diode which generates harmonics. The one I'm interested in is the 23rd on ~10.2GHz. As you can imagine, there's not much of it (about -65dbm). However, four amplifiers plus a couple of pipecap filters bring the signal up to ~+20dbm. Now I need to organise some on-air tests. |
| 11 May 2010 | I thought I'd try converting an old Ku band LNB into a 10GHz amplifier. All the components for the mixer and IF amplifiers were removed from the board. This leaves a two stage FET amplifier. SMA connectors were fitted for the input and output connections and coupled to the circuit with 1pF chip capacitors. The measured gain of the device is 15db (less than expected) and the output before compression is +7dbm. With enough drive, the output limits at +12dbm.
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| 09 May 2010 | I constructed another horn antenna for 10GHz. This one has a calculated gain of 20db and will be used as part of a compact microwave antenna system for use on field days. It has been mounted with the 24GHz horn such that it can be set for either vertical or horizontal polarisation.
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| 01 May 2010 | I tested the 70cm and 2.4GHz yagis in the field today and both worked well. The 70cm yagi was designed for 432MHz but the best match turned out to be on 435MHz. Not quite to plan, but it still works OK at 432MHz (i.e. the transmitter, an FT-897, didn't object). Good front to back. A couple of small lobes to the SE and SW (with the antenna point north) but certainly good enough for a portable field day antenna. |
| 30 Apr 2010 | I built another field day yagi using the T-Boom contruction technique. This one is an 8 element for 70cm with an overall length of 131cm. Again, I modified the design slightly to allow for rear mounting to the mast. I refrain from cutting out the entire vertical section of the boom at the driven element so that it retains it's rigidity. The driven element also goes through the boom. The vertical blue 'thing' on the driven element is just a plastic wall plug glued on to provide some support. There is also a 1/4 wave section of 75 ohm line between the driven element and the N connector to improve the match.
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| 29 Apr 2010 | Today I built a 10 element (i.e. small) yagi antenna for 2.4GHz field day use. The overall length is about 42cm. I used a modification of the T-Boom Yagi contruction technique described in the December 2009 issue of Amateur Radio magazine. I trimmed the width of the boom as I thought it might affect the performance because it was quite a large percentage of a wavelength. I also replaced the N connector with a length of hardline and an SMA socket at the rear.
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| 20 Apr 2010 | Last Thursday I aquired a 2.4GHz gridpak antenna which I intend to modify for use on 5.7GHz by changing the feed. I 'disassembled' (hammer, saw, etc.) the 2.4GHz to see what it was like. It's basically a dipole and reflector. The attached photo shows the dipole with it's 1/4 wave balun. Note that the solder joint between the coax inner and the brass dipole was broken!! I have yet to decide whether to use a bi-quad antenna or a small horn as the 5.7GHz feed.
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| 17 Apr 2010 | Conducted another test on 24GHz which was more successful this time. The signals were a bit noisy but otherwise quite readable over a distance of 5.1km. Given that I am only using a 20db gain horn and the other station (Tim, VK5ZT) was only using a 10db gain horn, this is quite good. The path loss over this distance is 134db and the received signal would be about -100db. The next step is to increase the antenna gain to 30db at each end (by using small dishes) which should, in theory, increase the line-of-sight range to ~160km for the same received signal strength. |
| 15 Apr 2010 | Finally completed transverters #2 and #3 for 3.4GHz. Now I need to do some field testing. Both of these are low power units. The output from transverter #2 is +14dbm and #3 is +17dbm. While EME is certainly out of the question this is more than sufficient for any terrestrial line-of-site contact. The LO on #3 is now only 2.3KHz high, so it's drifting back in the right direction as the crystal ages (it's been running almost continuously for 7 days).
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| 13 Apr 2010 | Completed the design and construction of an interface to go between the W1GHZ 3.4GHz transverter board and the FT-290R. Tested transverter #2 on air and all appears to be OK. Producing 25mW output. Now it just needs the antenna changeover relay.
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| 09 Apr 2010 | Web site updated to display this blog. |
| 08 Apr 2010 | Received EME175 LO kit in the mail. This is for my 3rd 3.4GHz transverter (trying variations of a W1GHZ design). Uses a 108.5333Mhz crystal for an output of 651.2MHz. Kit built and powered up. Output about 1.8KHz high. After 1 hour the output was 3.3KHz high. Seems to be ageing in the wrong direction!
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| 07 Apr 2010 | Second test on 24GHz using Gunn modules. Tx power ~+7dbm. Antenna ~20db horn. Signals heard over 3km range. Not as good as expected. Later discovered that the battery was going flat :-(
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