Sunday, July 10, 2016

Squeezing a few more Watts out of the Cool Blue ZIA Transceiver

Getting More Pout of your Rig!

So Ok, we all love to stand on the mountain top and scream I worked a station 12000 miles away on 20M SSB running 100 microwatts. Plausible? Yes! Possible? Yes! Practical on a daily basis? Probably not!
So what do you do to make consistent and reliable contacts? The 1st thing you do is get a decent antenna! A chunk of short wire hiding out in an attic space is not a good start! But a properly designed dipole at 30 feet is much better! Beyond that a beam at 33 feet is even better. So its the antenna for starters.
Next is the rig. You do not need to spend thousands of dollars on an appliance box to have consistent and reliable contacts.  A well designed homebrew transceiver running 5 to 10 watts will result in many contacts. Mating that 5 to 10 watts with an amp can really bore a hole in the ionosphere. I happen to have a really Big Amp -- a 3CPX1500A7 --which will do legal limit with about 45 watts of drive. At 5 to 10 watts it will easily do 400 to 500 watts output. Now that is a signal that can be heard -- keep in mind you are running a QRP transceiver -- only it is on steroids. I also have an SB200 and a couple of 100-150 Watt solid state amps.
In 2015, I built the ZIA Transceiver which has been subsequently updated in 2016 with a new paint job (Cool Blue) and the display has been changed from a Nokia 5110 to a 128X128 TFT. BTW using the Nokia 5110 is like doing brain surgery with a rusty spoon. I am really sorry I ever considered using such a poor device!

If you check my website at you can see the detail of how the ZIA was built. Instead of the usual IRF510 in the output I used a real RF transistor, a Motorola MRF260. This device is really intended for use at VHF but has been employed in this radio as this is what I had in the junk box. It can Pout in the 5 to 10 watt range. On a good day if you squinted properly you could see maybe 5 watts out.
Shown below is the 20M  ZIA parked next to the Nu-Rig (also Cool Blue) built in 2016.
About two weeks ago I tried to squeeze a few more watts out of the ZIA by replacing the MRF260 with a 2SC3133. Well as it turned out the two new "budget priced" 2SC3133's that I got from China were "FAKE" devices and immediately blew up in the circuit. So back to the MRF260. I should note that with the MRF260 the power out using the Solid State Amps (which are lower drive than the SB200) was about 100 Watts PEP. But I felt that 150 Watts should be easily attainable.
So now I went back to "noodling" how to squeeze out more power from the pre-driver and driver stage,  which is a direct lift from EMRFD (2N3904 and 2N3866 ) wherein it was stated that 300 Milliwatts was possible. That was not what I found. I guess this is the EMRFD gas mileage statement.
I made a few changes to that circuit and currently the Pout from the MRF260 is about 8 Watts PEP. I now easily hit 150 Watts out of the Solid State Amp! This past weekend was the IARU world wide contest. With the ZIA and the amp I worked about 30 stations. So much better than 5 or 8 watts alone. The changes to the EMRFD schematic include changing the devices to a 2N2222A and a 2SC2075 as well as the change in the emitter circuit of the 2N2222A. The second photo below shows the actual install in the rig.
This is the case of where we drained the swamp versus raising the bridge. I am very pleased and all the signal reports were excellent. If you look closely in the photo above you can see the 100 NF and the 50 Ohm resistor (actually 2 X 100 Ohms in parallel --what I had in the junk box).

Get more watts out of your rigs --and drive those amps!

Pete N6QW