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Technical Topics => The RF Workbench => Topic started by: Stretchyman on December 09, 2015, 1132 UTC
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I’m still musing over a design for much higher power, 200W or 400W carrier which will yield 1KW or 1.5KW on peaks.
Of course this won’t be running from 12V and will need DC’d mains or inverted from a pair of rather large 12V SLA’s.
Please forget any notion of a design like this running from any voltage less than 110V-150V as the currents will be just too high and kill efficiency.
Keeping the volts high means less current (for the same power) and therefore less I²R loss.
Three versions; below 2MHz, 3-4MHz & 6-7MHz.
Size wise it should fit in 2U 19” rack and not weigh more than 10LBs or so.
What I’m interested in is how many people would be interested in such a design?
I’ve had some interest from one notable on here and am willing to put in some effort early next year as my lab will be ready and can give the project some priority.
So, 1 KW O/P min, PWM Mod (obviously), DDS channel selection of user programmable 32Chs, will have to have some kind of protection for over current and high SWR etc.
Ideas please.
Str.
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There was a guy who was selling a Class H (?) PWM modulated AM tx kit in the back QRZ about 5 or 6 years ago. I never heard much about it other than the ads and some guys on the AM Window forum wondering about it.
The ad said it would produce a bit more than 500 watts carrier at 120 volts and the kit sold for around 600 dollars.
I'm sure if the price was right, there would be both Pirate and ham interest in your design.
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The problem with offering something of that scale for sale is that the price point will probably be beyond the reach of most of us, myself included. I'm working on something similar in my free time, but it will probably be a year before I have something to show for it. In the mean time, I gotta keep the bills paid ;)
+-RH
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Indeed, Price could be the problem as I was expecting to sell for £300 which is approx the same and at that price it would have to be a kit, building it would double the price.
How much power do folk really want? is always a question.
Soon as you go above a 10W carrier it means you can forget running from 12V and altho' I can get 25W carrier from a 24V supply even that's pushing it efficiency wise and its 10% better with 45V. So your going to need a mains/inverted supply.
May be able to do a 100W carrier (400W peak) for less? Would that be enough?
I notice folk on here aren't up to building much and while it's time consuming its fun but you do have to know what your doing!
Time is money as they say and I'm happy to recoup time spent designing and laying out PCB's from the sale of kits, building them makes them too expensive unless I do it for nothing, which frankly I'm not prepared to do (much!).
I'd definitely like to get some PCB's done for a higher power design but will only be able to supply kits.
We'll see.
Thanks for your input chaps.
Cheers from Blighty.
Stretchy.
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100W carrier I think would satisfy most ops, particularly if it sounds better than anything they've previously used. You could probably make the PCB design somewhat universal, so that more/larger fets could be added for more power, with the increased supply voltage of course. The 100W level is also nice because you can use passive cooling, no fan noise.
And now for the next illusion, make the same box do SSB ;) It can be done.
+-RH
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NO, it wont do SSB as it's class E and not linear.
I'm not interested in SSB, fine for comms, crap for tunes!
Sure tho' the design uses parallel FETs, voltage however would be the same, you need lots of volts to keep the losses down.
More FETs = more current = more power however.
The parts are not that expensive, a FET pair can only be $20, it's more the time designing and testing + the meagre amount I will sell (50?) which will drive up the cost.
If someone said 'Build me a 100' that would halve the cost immediately!
Str.
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100 watts of good sounding AM has normally been the pirate gold standard. It's why so many guys bust ass and get burns keeping those old Johnson rigs on the air.
Something that you could get 100 watts of good sounding AM out of without getting a hernia, now that's progress!
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Indeed, a notable on here has enquired and I could REALLY not believe he was hauling round a Johnson (Viking?), massive batteries and an invertor to get on the air.
Kind of 'Inspired' me to come up with something more 'Modern'
That stuff is over 50 years old and testament to its design that it's still being used, but really....fine for 'Nostalgic' purposes but otherwise...FFS!
Who Knows having something more portable may make it more popular!
We'll see.
Soon!
Str.
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That takes a high level of commitment...
... or maybe they should be committed...
something like that, anyway
;)
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Assuming 400W+ PEP capability, your going to need a supply voltage of at least 65V to deliver the peak power. I assume this will be a line-powered affair? I suppose you could use a large boost converter to get 12V up to 65V if battery operation is required.
+-RH
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100/120V A.C. Dc'd should give 120/150V.
Limey builders use 110V tranny's on building sites and you lot have 120V
So one design can be powered direct from mains or inverted from 12/24V batteries to the higher voltage.
Covered in my first post ;)
Oh and..... Yes JP, Definitely Committed!
:)
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I personally wouldn't bother with rectified mains until you get to the 500W carrier level or so, simply from a safety and cost standpoint. Switching supplies are so cheap, you can string 3 of them together to get 150VDC, quite enough for 500W CW. Also above that power level, power factor correction becomes compulsory for efficiency. It also helps reduce mains hum in the audio, unless your mod has humbucking.
BTW 'inverting' over here means running a power inverter to get 120VAC from 12VDC, hence why I asked about mains power.
+-RH
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Inverting is same here, not sure what we're not saying to each other!!
Whether the amp is plugged directly into (U.S.) mains or run from a (110V) isolation transformer or from an inverted supply will ALL lead to the same voltage.
120V A.C. (or 110 or whatever)
This will be rectified and smoothed inside the amp to 120/150V D.C.
Cost is a bridge rectifier and a smoothing cap.
3 PSU's are way to big as the amp is not even as big as one of them!
Choice can be up to the end user.
The 110V isolation trannies are very cheap and safe enough and that would be my recommendation.
Str.
:)
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The problem with that is you still have the weight problem to contend with. I like rack mount stuff, there's just something 'official' looking about it. A relatively shallow 3U chassis could contain up to 1KW, and weigh less than 25 pounds. At the 1KW level even considering modest efficiency, you still need around 1600W during 100% modulation, and that takes a rather heavy transformer. Build a PFC boost circuit to get 250VDC, isolate the drive, and there you go. I'd call that progress. Leave the iron to the scrappers ;)
+-RH
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If it's in a rack it's in the house and you may as well use SMPSU's
I'm looking at 'Portable' use, hence the 110V from a genni or inverted from 12/24/48V D.C.
The PSU can be left up to the user anyway, I'm just designing the amp and PWM!
;D
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I always like to look at the whole package, you never know what someone may try to hack up.
Just because it's in a rack doesn't necessarily mean it's indoors. My TX lives in a road case and spends quite a bit of time with nothing but stars over it :)
Battery power is appealing if your operating from somewhere where you are not necessarily welcome, someone's field for instance, or back parts of a park. Generator power in these instances, even with modern inverter type generators can raise the 'here I am' flag, as if a tall antenna didn't say it already.
+-RH
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I'm trying to keep costs to a minimum. I wont be supplying any power, just 'recommendations'.
It will need 110-120V A.C. (or D.C.) and 24V (probably) as the drivers need 18V.
Also I'm not that interested in selling built units, one or two maybe to 'notables' but no more.
The kit will be fairly simple to put together.
:)
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Very interesting thread guys but I've been lurking because the subject matter is mostly above my skill level. I think you're on the right track by designing for a less ambitious power level Stretchy. Feedback I've received over the years from homebrewpirateradio group members who value portability do so for TWO reasons. First of course is the security of being able to transmit from - WHEREVER. Secondly, many ops live in:
Trailer parks
Apartment Buildings
Dense Subdivisions
All these situations find the op in very close proximity to neighbors and all their poorly-filtered consumer electronic devices. The 10-20 watt carrier level minimizes bleed through problems and yet works quite well for NVIS mode operation, which is what a typical sub-optimal antenna is best for anyway. I agree with Redhat - generators are a bust. Even the quietest are so damn noisy that you need to be surrounded by many many acres of nothing or you'll be attracting the wrong kind of attention. I'm guessing that you'll find some takers for a 100 watt carrier level transmitter. Good luck with it...
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It is true, battery operation above a certain power level begins to get ridiculous, and that point seems to be 100W-250W. Above that, generators or shore power are the logical choice.
+-RH
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You can series the batteries so you get 24V or 48V (or whatever) and invert to a higher voltage from there.
Yes gennis are noisy and not advocating their use (altho' I would as I have a site miles from anywhere) and am just trying to cover as many bases as possible.
The (RF/PWM) design will (should) push close to a KW (@ 150V) and of course will need many volts hence my 120/150V supply.
However it will work at ANY voltage, half the volts = quarter of the power.
:)
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OK, Have a working design, at last!
24V = 100W so 48V will yeald 400W.
The design was built with much higher voltages in mind (150V) but have obtained decent efficiency (88%) at this relatively low voltage.
Using a higher voltage I expect 95% efficiency.
I have a PWM modulator or conventional Audio amp and mod tranny to use as modulators, PWM needs twice the voltage as conventional method.
Check out attached image.
Str.