Hi power HF amplifiers

[A.Z.]

But the RF output power meter is calibrated to indicate a limit of 1500 watts.  All 1500 watt amplifiers should be able to put out some amount more than 1500 watts for adequate linearity at 1500 watts.  This one just appears overbuilt more than most, and should also get better operating life than most.

Reading various reviews of the Chinese FU-728F tube makes me think that the power claims are exaggerated.

Don't know, but reading the comment from W8IDL here

https://www.eham.net/reviews/view-product?id=11595

he states the following

Have had the Emtron DX-3SP here for about 2 years now and have used it extensively. Can it do well over 4.5KW out? Yes - into a good dummy load - but I run mine at 1.5KW out on-the-air. Under 25 Watts in gets you 1.5KW out all day long in any mode. At the top end of 10 meters (29.7 MHz) it takes about 32 Watts in to get 1.5KW out. That is excellent performance!

so apparently the amplifier can really ouput over 4KW but he says he's using it at/below legal limit; fine and as I wrote in the initial post, such a thing would allow the amplifier tubes to have much less stress and last longer, yet I doubt that people "out there" would buy such an amplifier (or a similar one, the one I linked was just as an example) and run it at lower power, also since a (say) 2KW amplifier could be run at 1.5KW or less and allow obtaining the same result (less stress to tubes), so again, what's the purpose for a 5KW Ham HF amplifier ?

[gargle]

I may be a little naive but I think there is 2 aims :
- less power in lamp which accept much more, so longer life
- amp in the "middle" of the band, where it's the most linear, to reduce distortion.

But there is also a lot of ham people which consider that amp is life, and don't know the proverb :
So much for the ANTENNA
So much for the HAM STATION

 

[A.Z.]

So much for the ANTENNA
So much for the HAM STATION

or "90% of a station is the antenna system" (and I'd humbly add the grounding system too,)

[m3vuv]

to make the power gen/utility companys lots of money,i have a homebrew hf amp that will tx about 1700w but never use it when i saw what it draws from the mains,good way for big leccy bills for no real gain as ear as i see it,also being an m3 here a good way to get busted!/nicked.

[cdev]

Commercial broadcast, military, governments (diplomatic services?) demining, (ground penetrating radar). cooking, baking, soldering? Diathermy?

Perhaps there are special licenses that allow use of more than the usual power limit for certain purposes like bouncing a signal off the moon?

[cdev]

Commercial broadcast, military, governments (diplomatic services?) demining, (ground penetrating radar). cooking, baking, soldering? Diathermy?

Perhaps there are special licenses that allow use of more than the usual power limit for certain purposes like bouncing a signal off the moon?

To do that one doesn't need the legal limit, just a high gain antenna and a bit of power (enough to exceed the noise level at the receiver which presumably is also using a highly directional antenna).


AS I understand it its getting easier and easier to do, affordably and legally. Especially with digital modes.

I have some small directional antennas that could be combined with external dishes (As a feed) to give the requisite gain. Wonder if I could receive hams working EME?

When I lived elsewhere, at a restaurant equipment shop I found chrome plated steel pot lid thats a perfect parabola (as shown by its ability to focus sunlight into a point with absolute precision. It makes my eyes hurt just to think about it. )

Anyway, this does not do much at low microwave frequencies (I suspect for wifi it might deliver ~20 db gain or so.) but the higher you go the more gain you get. This is roughtly an 18 inch dish..  A 1 meter dish is fairly affordable and easy to find. These are popular for direct-TV like services.

Hige parabolic dishes are very impractical because of wind loading in storms. But smaller ones would work for EME on higher bands.

[geggi1]

Remember that this rating is on CW and SSB. If the linear is used on AM the maximum power output to not damage the valves is probably 30%-40% of the maximum rating (1200W - 1600W) that is very close to legal limit in the US, Australia and probably plenty of other countries.

[bd139]

Another legal reason is using compromised antennas or feeds. For example your ERP might be within the legal limit but the power you stick up the feed might be considerably higher. If you have a massive beam antenna remotely located then that is perfectly reasonable.

But mostly it's these retards I expect



Not that I do it now but I kept my shit under 10W apart from a surprisingly successful IRF530 based amp which ran a whole 40W on CW.

[cdev]

I didn't realize people got credit for cable loss and got to make it up. If that is what you are proposing.

Are you sure?

Also, how are directional antennas handled. I could see this getting kind of complicated quickly and where regulatory matters go, sometimes simpler is better. Also, the law shouldn't discourage or penalize people for good practices considerate of the resource. People should use the least power and the antenna, seems preferably a directional antenna - not wasting signal where its not going to help...whatever is necessary to make the link work, IMHO.

[cdev]

Thats an illegal CB amplifier. His voice makes me think he's from the southern US.

Do those peoples signals make it to the EU? I bet some of them do.

[bd139]

Regarding feed loss, that is one thing yes. But directional antennas on low frequencies are quite large. Even a 40m yagi is impractical for most. So you have to put up with somewhat inefficient radiators potentially.

On longer wavelength bands things get interesting though. For example on 2200m expect to throw 170 watts down the feedline and get 0.4W EIRP. To hit the limit of 5W EIRP in some regions, you'd have to throw 2125 watts down that feed line.

Also on top of that some of the modulations are not very bandwidth efficient. AM for example is terrible. SSB is marginal. CW and FT8 etc are excellent. To get a better SnR you have to throw much more power down the line on AM or SSB to reach the same distance.

CW is my favourite though. I managed to hit Tasmania from the UK on 2 watts thanks to some glorious propagation conditions once!

[cdev]

Transistors that work at LF frequencies would be quite affordable, most here likely already have em..

For antenna, make a mag loop out of several turns of copper pipe or maybe coax (for the braid and coax connectors) , and a big homemade capacitor, maybe?

It seems as if it makes sense to use a magnetic loop antenna or similar so you wont need radials.. Cuts down on ground losses, I would guess..


Look at helical magnetic loops.. They look like a good approach.

[bd139]

IRF530 MOSFETs seem to be the workhorse for this stuff. Slightly explodey but cheap as anything.

Google for some 630m and 2200m loading coils. That’s what people seem to be doing. The mag loops would still be too big.

[tkamiya]

In my day's in Japan, it was possible to purchase Henry 8K.  A remote capable unit produces 10KW at 100% duty cycle.  Of course I neither had a budget or desire to buy such a monster.

Some serious contesters have have quite a few of way over legal limit amplifiers.  Somewhere on Internet, there is a 40KW amp someone designed as part of dare. 

My max is 100 watts.  I never needed anything more.

[knapik]

We have an SPE 2 kW HF amplifier at work (more than the legal limit for amateur radio over here) because we calibrate in line power meters, so all of that energy is being dumped right into a termination anyways. Even with 2kW we still have to turn down a lot of power meters because they're rated at a maximum of 10 kW.

[thinkfat]

I do remember a story of a US ham operator who saved a satellite by overpowering a leaking oscillator in one of its transponders that clogged the command channel, from his ground station. He sent a command to disable the transponder, saving the satellite. His signal was "louder" than the leak from the LO. I don't quite remember, but it was one of the AMSAT vehicles.

[bd139]

Probably followed immediately by the FCC turning up 

[rfclown]

I worked at Sunair for a short time. Our HF transceiver had an output of 125W, but the external amplifiers were 500W, 5kW and 10kW. Their market wasn't amateur radio.

[thinkfat]

I do remember a story of a US ham operator who saved a satellite by overpowering a leaking oscillator in one of its transponders that clogged the command channel, from his ground station. He sent a command to disable the transponder, saving the satellite. His signal was "louder" than the leak from the LO. I don't quite remember, but it was one of the AMSAT vehicles.

I finally found a reference of this:
http://om6bb.bab.sk/files/HAM%20kniznica/Magaziny/QST/09%20September%202000%20QST.pdf

The HAM in question is David Blaschke, W5UN, and the satellite was DOVE-OSCAR 17.

Not easy to find stuff that predates Y2K, on the internet.

[Jr460]

Market for HF high power......

Sure, long ago when I was a kid went on a tour of the VOA site about 5 miles from me.   Rather than a normal tour, it was a bunch of HAMs and most of the operations people at the VOA site were Hams.   We saw all the cool stuff and got shown things that most people had no idea what it was.

They did crazy things like 500KW, yes half a million, HF band into a curtain antenna to beam a double side band suppressed carrier with a different program in each sideband to somewhere in Africa.   And that was just one of the transmitters.

In the winter the building was heated from steam from the cooling water around the tubes.   The audio transformer of an AM transmitter, B+ for RF output tubes it runthru it, was as tall as I was at the time.   You could hear what was broadcast if you were in the right room because the steel laminations were not perfectly tight and and so large that they produced some sound.

Now the VOA site with all the towers supporting the antennas and feed lines are gone, now a park.   The operations/transmitter building remains for history.

[M0HZH]

1. There are 194 more countries besides the US and they all have different legal limits for amateur radio; Canada has 2.25kW for example, others allow special experimental licenses with higher limits (UK can allow up to 2kW) etc.

2. Many amplifiers are rated for amateur radio typical duty cycle, which is quite low and not really standardised; solid amplifiers are rated for the ICAS (Intermittent Commercial and Amateur Service) standard, which is 50% duty cycle (5 minutes on / 5 minutes off) but tested in a dummy load. In a contest you might exceed 50%, continuously for 48+ hours, in a antenna system that doesn't have perfect SWR across the entire band, in a room that might get too hot; you need an amplifier "normally" rated much higher than the legal limit to be able to do that many weekends a year, for many years, without failing.

3. People like to have more power available if needed for that special DX pileup, even if they break the limits .

[A.Z.]

1. There are 194 more countries besides the US and they all have different legal limits for amateur radio; Canada has 2.25kW for example, others allow special experimental licenses with higher limits (UK can allow up to 2kW) etc.

2. Many amplifiers are rated for amateur radio typical duty cycle, which is quite low and not really standardised; solid amplifiers are rated for the ICAS (Intermittent Commercial and Amateur Service) standard, which is 50% duty cycle (5 minutes on / 5 minutes off) but tested in a dummy load. In a contest you might exceed 50%, continuously for 48+ hours, in a antenna system that doesn't have perfect SWR across the entire band, in a room that might get too hot; you need an amplifier "normally" rated much higher than the legal limit to be able to do that many weekends a year, for many years, without failing.

3. People like to have more power available if needed for that special DX pileup, even if they break the limits .

All good points, but then one sees stuff like these

http://www.dc9dz.de/en/tsunami.html

http://www.dc9dz.de/en/tsunami100k.html

and starts wondering if that's just "to have more power available if needed" 

[M0HZH]

I see DC9DZ's projects more like engineering achievements, but there are some in the wild; of course there are people running them ilegally.

Also, the numbers are very misleading; "100kW" RF output with a 30kVA power supply, that's probably 15kW real output with the tube massively outside spec (rated for 11kV anode voltage, absolute max limit 13kV, ran at 17kV here). A realistic safe-ish number is probably 10kW for RF output.

[mag_therm]

20m ft8  is getting spoiled by appliances in USA day time  with their wick turned up too high.
FT8 reception can't use conventional AGC.

Yesterday there were transmissions coming in here in Michigan, more than S9 +20dB

If wsjr-x gets a signal over its +80dB level, it will stop decoding.
Also the computer sound card can clip.
Yesterday I turned the receiver IF down by about 20dB in the day, and then progressively turned it up overnight.

I am thinking about a very slow AGC based on out of band noise level.

[cdev]

A better antenna seems to me to almost always make more sense than more power.  Unless people like a one way monologue over a conversation!