Author: Rob Powell

CQ Contest SSB 2023

Let me tell you why living in an RF quiet environment and using vertical antennas sucks big during the big contests. When you hear everyone, you cannot hear anyone. The bands are just endless heterodynes. To say I found the CQWW contest frustrating this weekend was an understatement. Hitting the bands during the prime time here and tuning up and down was an exercise in futility. Pretty much what was happening was that after identifying a signal and tuning to it, by the time I got close to being in tune, another greater heterodyne swamped out the signal I was hearing and I ended up in a tug of war between the two of them.

This was not so much a problem when conditions were a little quieter, and stations were spread out a bit, like greater than 1500hz between stations so that focusing on the one signal was much easier, but when there was a station every 500hz or so because i am an idiot who thinks working his 3 band dxcc on vertical antennas is a great idea, it was very impossible to tune to one signal only unless they were a few S points stronger than all the heterodynes combined.

Now i was not going for a score, I was just looking for new countries or phone slots with no intention of entering a log. So I never did make a lot of contacts, but managed to work Cambodia for a slot on 15, Antigua and Barbuda as well as Bonaire Island both for ATNO on 20m. All 3 were early in the morning here, during the quite time, not during the afternoon prime time and even then.

All in all I can’t complain, but I tell you what,  god I need to get a beam up so that I can null out a great part of the world so that I can hear at least some place clearly. I have the bits here to get a 2 elephants yogi on 20, 15 and 10m, but really want to get 3 band dxcc first, I am 85 confirmed on 40m out of 106 worked, with about 10 that should confirm on lotw. So i don’t need many more, i just need to get up early in the morning to work some more easy ones in the EU. I just need to shit the bed a few times and stay up when i go for a 3am piss.

In other great news, boards and parts should arrive later this week and then I can get to building the new thing 🙂 Oh and a new monitor is on its way also, turns out the noise issues I have been having on 10m is all due to the psu in my monitor. Nothing is ever simple HAHAHA

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Tx Rx and Antenna Switching

 

Started to design up the next piece of the amp puzzle. transmit and receive switching as well as various antenna ports for all the antennas. While the graphic shows BNC connectors, they are in fact So239’s. On transmit the exciter comes in the radio port, gets sent to the amp input, the output of the low pass filters goes to the amp out and gets routed to one of the antenna ports. On receive the antenna port bypasses everything and gets routed to the radio port and receiver.

The transmit and receive relays are controlled by a PNP switch which when its base is pulled to ground, switches the relays over. The entire thing will be controlled by a micro controller with either a touch screen or some buttons. Have not decided on which yet, that part is still in the what am i going to do stage 🙂 If i really wanted to go poverty, i could use a 3 position switch on the antenna relays. But who really wants to be agricultural when you can go all ferrari.

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Amplifier AC Power Supply Requirements

So today I learned a thing. Like why linear amp manufacturers spec their AC requirements so high. Like the Elecraft amp calls for 20A at 240v and a bunch of others say 15A etc. The reason why I am thinking about this is because I have been thinking about upgrading my license and then doing some sums to work out the costs of adding an amp to the line up.

If these things really did require ALL THE AC AMPS, I would have to pull a dedicated 20A line from the sub panel in the garage. Lucky there is room on the board to do this, but, its going to cost about $1500 to have a elechicken come and take half the roof off the house to pull a cable to where it needs to go and that is on top of the costs of an amp and the like.

My radio room already is on a 20A circuit that it shares with the water pump, bathroom and laundry, so leaving some overhead for the freezer and washing machine, there is room to spare, but not 15A, maybe 10A and then you would not want the wife to dry her hair in the bathroom. LOL

So why do these things need so much current? Inefficient power supplies. If they are using linear power supplies, because hams are scared of switch mode supplies, they might only be at best 60% efficient compared to say 80% efficient for even the worst switcher from MeanWell. And there is where I had my eureka moment. Math will give me a rough idea of the actual AC current requirements for any particular amp.

AC AMPS == DC Power (watts) / (Power Factor * AC Volts * Efficiency%)

So for your typical LDmos amp these days with 50V at 30A a maximum of 1500 watts, with linear power supplies 1500/(0.8*240*60%) you are looking at 13 Amps AC (guessing the power factor here). Compare that to a fairly efficient switch mode supply with power factor correction and your total AC current draw is going to be around 8 Amps or better.

This got me thinking, legal limit here is 400w and those numbers are for something closer to US power limits. So in theory, without knowing what the actual DC Power requirements are, but lets say 50V at 10A, thats 500 DC Watts and with a 90% efficient switch mode power supply we are looking at only around 2.5A AC.

That is not going to stress the existing household circuitry at all, in fact there is more than enough capacity to not even stress things even a tiny little bit. So maybe this upgrade and build and amp, yeah build one not buy it because I have the skills to design the boards and write the code to control it all, could be done for a reasonable cost, not in the 5 to 10K kind of mark.

So maybe this stupidity is actually within reach and I should give a little more thought to upgrading the license. Currently I am really close to finishing off 40m and 10m dxcc which will give me 4 bands and for the 5th band we are talking 80m and for that having 400w on tap with crappy dipole antennas might make dxcc a lot less painful.

So who knows, but watch this space. 🙂

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The 100 Club

Ignore all the burned flux residue, thats just there because I managed to toast all the fets when I accidentally tried to drive a 100w amp with 100w. HAHAHA, dumb arse move i know but shit happens. The good thing is, blowing up $4 worth of parts does not smart like blowing up $200 worth of LdMos.

But as far as things go, being a proof of concept, I really could not have been more happier. 100w out on 40m dropping down to 50w out on 10m, with little to no thought going into the design, I am sure I can improve the higher frequencies with a bit more thought on the design, input matching and general layout.

And on the subject of layout, I have worked out a lot of things i can do to improve things, like rotating the fets 180 degrees and using flood fills for the output traces. I also need to add in Tx/Rx switching and the like to make it perfect.

As for its performance, it draws about 6A at 13.8V, even with the sub optimum heatsink that is passively cooled, after 30 minutes of 50% duty cycle, the case of the fets did not get beyond 65 Deg C. All in all, i am very pleased with the performance and now get to redesign it, add in the improvements and build it all together into a box with filters and call it a thing 🙂

 

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More Toy Sets

I got asked to make a few toy sets for Christmas presents for the grand kids of a friend of the missus. I should have had these done weeks ago, but for the last 3 weeks I have been dealing with either the flu or covid. Either or, I have been feeling like shit and feeling like I have pneumonia. I am on the mend now, finally, but still do not have much endurance. Either or, i need to have them done by Friday next week, so i gotta suck it up and get her done. After 3 weeks of doing fuck all other than a bit of radio and a lot of sleeping, its been good to get into the shed and do a few hours of woodworking.

Getting the hand saws done.

What is done already, yeah I am making 4 sets at one time.

Whats left to go. 3 or 4 hours and I should be able to have it all complete.

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