100w Dummy Load

Not all builds are big and fancy. Sometimes you just have to build something to do the job. This 100w dummy load is 20 x 5w resistors in parallel, nothing fancy and should handle the 60w i wish to throw at it for a couple of amplifier projects i have sitting here.

The 30w dummy load i build previously, 10 x 3w resistors was starting to get warm around the 25w mark, so i think this new one should stay cool to 80 or 80w quite easily. I will add a 12v fan to the case if i need to cool it and give it more power at some stage.


Resistors soldered to the board in a grid 4×5.


Being 5% parts you expect some variation, but near enough to a 50 ohm load as you can get.


RFPM1 RF Meter Kit by vk3aqz Kits.


The RFPM1 RF Power Meter Kit by http://www.vk3aqzkits.com/   Let me preface this by saying, if this works 1/2 as good as the attention to detail that has gone into presenting this kit, it should  be nothing short of awesome. Opening the box is a WOW moment, as the level of detail and care that has gone into making this kit is evident. Lou VK3AQZ takes customer service to a whole new level, where most kits manufacturers give you a box and a bazillion parts, as well as a few photocopied pages, the RFPM1 RF Power Meter Kit is immaculately presented.


Key to the whole device is the RF probe, small parts contained in pill boxes to keep the separate and so they don’t get lost in transit is a really nice touch. You will also notice solder in 2 different gauges, one for SMT work and one for thought holes. That is just unheard of from anyone.


The case is well routed and drilled, so there are no expectations for you to cut and drill anything.


Parts for the rest of the unit are all contained within the case, both the analog and digital meters have been checked before leaving.

solar-rfmeter-10 solar-rfmeter-8

Build notes for both parts of the kit are in full colour, printed on laser, the kit contains 2 dvd’s showing the build process as well as many videos on how to use the unit for a number of different test scenarios. All parts have been ticked off the part list as they are packed and hand written notes about other bits not contained in that list have also been added.


The level of care and detail are very evident and Lou has really gone out of his way to produce a wonderful kit, made with high quality parts and I am looking forward to spending some time putting this together and using it in all the filter experiments i have planned. I might not have the money to buy an expensive frequency analyser, but with this and the 12mhz function generator I have, i can still find 3db points and measure the level of harmonics after low pass filtering. And one thing im looking forward to, is being able to set the gain on buffers used on mixers without having to convert rms volts into dbm, as this RF meter gives to the power in dB’s. Awesome.


Solar Panels for Portable

One thing i have found on the 3 day camping trips is that my battery gets pretty much hammered. Sure its 100ah, but after you have taken 40 to 50ah out of it, its pretty much done all it can do for the high current demands of a FT-897. When you see the voltage on TX get into the 11 and 10v range, you know you are not far away from hurting your battery permanently.
Maximum cycles and ultimately life of a deep cycle battery, can only be had if you do not discharge much more than 50% of the total battery capacity. Sure a deep cycle can be deeply cycled, but doing it often will lead to sulphation of the plates and poor holding capacity. Being the tight arse that I am HIHI, I wish for my cheap Chinese import battery to last for as many cycles as possible and with that in mind, i bought a solar charge kit.

So the kit i bought is a MaxRay 80w folding solar kit off Ebay. Total cost $140 delivered. Which comes with a 10A charge controller, 9m lead with 50A Anderson plug, carry bag and Anderson plug with battery clips.



Build quality seems ok, one small issue is the wiring to the charge controller was not done correctly, this is something i will rectify before i use it. Other than that, it seems like a nice enough unit. I will put it in the sun tomorrow and measure its voltage and current delivery to see just how close to spec it really is. That will be the real rest for this. But, if it keeps both our deep cycles charged for camping, it will mean i can take other high power devices and not have to worry about hurting the batteries. A fridge will be next and I think the boss wants a fan in the camper as well. HIHI.



Filters Filters and More Filters

Filters, its a huge subject with many books and millions of words devoted to trying to better understand the subject. Filters are the only real non amplifier stage in most radio designs. the covers a number of different types, Low Pass, High Pass, Band Pass, Notch, and come in a number of configurations, Chebychev, Butterworth, Cohn, Sallen Key and can be implemented either, passively with inductors and capacitors or with crystal or ceramic resonators or actively with Op Amps or CMOS Switched Capacitance.

So filters are by no means a trivial topic of learning, but one that can keep an interested person busy for quite a long time. It is also one I intend to fully explore over the next few months to try and come to a better understanding. Of all the filter types, i have only ever really built low pass filters for harmonic suppression in PA amplifiers. However, over the next few weeks I shall start experimenting with other filter types, starting with passive filters for audio, CW and SSB audio band pass filters, as these will be used in a Direct Conversion tranceiver project i have been working on for sometime on and off.

The next major filter type i wish to tackle is the crystal ladder filter, using ceramic resonators for 455khz 2nd IF of my Icom 718 radio. An Icom filter coast close to 300 bucks, a collins filter about 200 bucks, so i thought i would give the whole idea of home brewing a filter a go. Even if this is a total failure, i will have learned a lot about filter design and the motional parameters of xtals and ceramic resonators. Parts are on order from China, and as soon as they arrive I will start on the project.


To determine the motional parameters of a xtal or ceramic resonator you use a test rig like the schematic above. You insert a sine wave around the freq of the device into the input, measure the amplitude of the freq on the output with an rf meter, varying the frequency till you find the frequency that gives the maximum signal amplitude on each of the 3 sections, no capacitance, 10 and 27pf. With those numbers you can then do some math to get the series and parallel resonances of the xtals to use in designing the filter in a program like “Dishal” by DJ6EV.

More on filters to come.


Bias Networks for RF Devices

Bias Circuits for RF Devices by Iulian Rosu, YO3DAC / VA3IUL


I came across this PDF while trawling the net looking up information about something or another and found it to be a really great resource on biasing all sorts of devices covering just about every device the modern ham might actually use in a project.  My thanks goes to the author Iulian Rosu and i hope others might find this document as useful as i have in understanding a rather complex subject.



WWFF VKFF Mass Activation Weekend

On the weekend of the 27-29th of November, Australia had its first mass activation weekend for the WWFF/VKFF programs. Over the course of the weekend, some 80 something national parks were activated, many for the very first time. Being a WWFF/VKFF nut myself, I did my part and activated 5 parks. I was planning on activating a 6th park, but ran out of time and more importantly I was running out of battery. A 100Ah can only do so much before even it has been hit too hard and needs time on a charger.

Park Name Number of QSO First time Activation
1 Lockyer National Park 20 Yes
2 Lockyer Recovery National Park 17 Yes
3 Crows Nest National Park 63 Yes
4 Hampton National Park 26 Yes
5 Geham National Park 31 Yes


Lockyer NP and Recovery NP

On the Friday while heading out to Crows Nest, I activated these 2 parks. Lockyer is a rather nice national park and one i wish i had more time on the day to explore. With plenty of fire trails and dirt roads to hike on as well as some awesome scenery. Sadly i had exactly 1 hour in each location as we were on a tight schedule to get to Crows Nest to set up camp for the night. Qualified both parks for VKFF which is nice. Contacts made on 40 and 15m.

Crows Nest NP

Crows Nest was the base camp for all my weekend activities, we camped here Friday and Saturday nights having the whole camp ground pretty much to ourselves all weekend with the only other campers arriving about 4pm on Sat afternoon. The park itself is actually worth the visit, there are a number of walks that can be undertaking to some rather impressive water falls and to a lookout. The camp ground is basic, with well defined sites each with its own small fire pit and BBQ, toilets are long drops and there are cold showers as well.

This was going to be my night time radio operating location, but the weather gods had different ideas. With storm cells all around us both nights, 40m was a right off with 40db over storm static. Thankfully 15m came to the rescue here with a number of dx contacts being made, to bump up the numbers in my log and qualify the park for both WWFF and VKFF. Contacts were made in Denmark, Germany, Guam, New Zealand, Japan, Sri Lanka, Belgium as well as most states of VK, 1,2,3,4,5,6,7,8. All in all i was pleased with how things went from this park under some very trying conditions.


Friday afternoon, Crows Nest NP Base Camp, radioing even before we have camp fully setup HIH.



This picture is representative of the open woodland scrub that is typical around the Crows Nest region.

Hampton NP

This is a tiny little park in the middle of Hampton township, it is not much to look at. Setup the radio gear near a pile of Lantana and looked at the road near by. I spent about an hour here, making 26 qso’s and a few park to park contacts. Contacts made on 40 and 15m.

Geham NP

Like Hampton, Geham is a tiny little park near Geham township, It was much more pleasant on the eyes, Being mostly native remnant vegetation and tall timbers. I spent about 90mins here active on the radio, making 31 qso and a few park to parks. Contacts made on 40 and 15m.

Noise: I took this short video just to show how bad the storm static was on 40m both nights, 15m was somewhat better, but still loud crashes rather than the constant noise that 40m was.