Judging by the number of emails I have received over the last two months since I began publishing details of my construction activities in the Microwave Bands, there are a great number of Amateur Radio operators who would like to participate in the challenge of the Microwave Bands but are unsure as to how to start.
I have written this article to show how I went about starting!
However while it is clear from surfing the Internet, that there are many ways to get started in the world of microwaves, I decided to “bite the bullet so to speak” and have a go at doing it my way!
To begin with, I decided that I was happy to build the entire project which inevitably involved working with “surface mount” components and while I appreciate not everyone has had experience in this area of construction, it is undoubtedly the way of the future for most electronic solutions.
In deciding to take the route of using surface mounted components, the age old problem of component lead lengths in the Microwave spectrum becomes one less problem to deal with!
The next question that presented itself was; do I really want to start from scratch or would it be more logical to start with a ” kit of parts”.
To cut a long story short, I decided to embark on the journey by using a kit. This decision overcame a number of issues; the development of a printed circuit board, the sourcing of all the components and by taking this route a tried and tested solution presented itself. These factors coupled with the desire to use minimal test equipment to achieve a positive result was the final consideration that brought this project sharply into focus.
This last issue is not really a problem for me as I have, at my disposal, the resources of a fully operational development/prototyping laboratory but I wanted to produce a project that did not rely on any of these resources and I guess that deep down I just wanted to see how hard it would be to become QRV on the Microwave Bands using simple everyday tools.
As mentioned previously, I have spent considerable time on the Internet looking at how other people became QRV on the Microwave Bands and I soon concluded that DB6NT’s experience and reputation for quality, simplicity and value for money was hard to beat. Further his designs and ultimate tune up procedures made it impossible to dismiss.
In addition to the above, the solutions offered by DB6NT came in a kit form with every component supplied and at an overall cost that was better than any other solution I could find!
In deciding on this course of action, it is not my intension to indicate that there are no other solutions available; there are, but they just didn’t work for me!
Over the last two years I have built a number of these kits for a variety of Microwave band and reconditioned quite a few of the assembled kits that came from a number of sources, that for a variety of reasons, never really became operational on the air due to inbuilt faults or incorrectly placed components. In ALL of the cases the kits once correctly assembled worked well and were easy to tune. With respect to two of these kits that I re-furbished, I stripped the boards and started again. During this refurbishment process I only needed to replace the odd device or component that had been damaged by heat. The printed circuit board in both instances survived, a testomney to the quality of the printed circuit boards supplied with the DB6NT kits.
It is not my intension to go through the component assembly of the DB6NT Kits as there are many examples available on the Internet outlining the precautions and procedures to be used when working with these products. In addition there is the potential to download assembly instruction for all of the DB6NT products.
The tune up process is very simple indeed and can be accomplished by using a standard “multimeter”. I believe one of the reasons that this process is so simple relates to the basic design. Once the tune-up stage is started it soon becomes obvious that when tuning the individual tuned circuits, there is only one resonant point in the tuning range! This fact alone makes the entire tune-up process quite straight forward and easy to complete.
Upon completion of each microwave system that I have built, I used the range of test equipment at my disposal, to check the results obtained using the simplified tune up process and in each case I was unable to better the tuning. In the case of the transmitter, the output power produced was clean with an output equal to or slightly greater than the published specifications.
The accompanying images show the Basic 10 Ghz transverter assembly and the associated hardware used. This unit produces a clean 250mw output at 10Ghz from a 144Mhz – YAESU FT 817ND Transceiver driving with a 1W output.
The project was assembled into a “die-cast” box that I pre-drilled as shown. The small brackets were made from aluminum scrap, again pre-drilled as required. All of the basic components (switches, connectors, etc) are readily available from a number of component suppliers. Yes I do have a junk box with all manner of components that I could have used however because I wanted to replicate the design for most of the Microwave Bands and I wanted to standardise on all of the components where possible.
The meter scale was developed in Photoshop and then printed onto “matt” photographic paper using a colour laser printer. The original meter scale was removed an used as a template. The meter has a 50uA movement.
The RF interconnections are based on UT141 hardline and associated SMA connectors. This coax is simple to use with acceptable performance to 10Ghz but this can be stretched to 20Ghz in short runs. The coax to waveguide right angle converter that I have used to feed the “prime focus” dish is an “N type” made by HP however there are many brands that are readily available on eBay.
The SMA antenna change over relay is made by “Teledyne” that has a 28 volt coil and has a maxium usuable frequency of 18Ghz. These are also available on eBay.
This relay is driven by a simple power supply based on a NE555 timer. I don’t know the designer of the circuit, but I have used this standard circuit for a number of years in a variety of projects with great success. The ciruit was published in the earley 1990’s in a NE555 time application note. There are many similar power supplies that can be used, all of which are capable of driving the relay successfully.
In assembling this microwave project I have routed the control circuit wiring through aluminium tubing. This is a technique that was pioneered by NEC in their microwave link equipment in the 1980’s. It provides good RF bypassing / shielding and because most of the impedances encounted in this project are low, there is little chance of RF feedback being an issue, however when this technique is used, this issue is eliminated. (To prove a point I ran an RF sniffer around the system while transmitting and could not detect the presence of any unwanted / stray RF). It also provides an ideal solution for maintaining stability of all control circuits especially when the equipment is moved from location to location for portable operation.
The angle bracket at the base of the assembly allows the unit to be mounted on a photographic tripod.
The Prime Focus Dish used in this solution is 300mm in diameter and was originally used for aircraft weather radar with a gain of 21dbi.
The unit has been a lot of fun to construct and put into operation. Just as an aside the kit used in this project was purchased off the internet in a rather dilapidated state requiring a complete rebuild. (All the components were stripped off the printed circuit board and I started again). What did it cost on eBay – A$80 a bargain and without a doubt well worth the restoration effort!
The observant among you will have noticed in the initial assembly of the project components the “antenna change over relay” had its terminals on the top of the relay, however the images of the finished unit has the connections on the bottom. The reason for this change resulted from a faulty / intermittent relay that had to be replaced. This by the way, was the only failure that happened in the assembly of this project.
I hope I have answered some of the questions that your emails raised and has given someone the incentive to “give it a go” and become QRV on the Microwave Bands.