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Author Topic: 2m amplifiers???  (Read 2030 times)
KG9ZTX
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Posts: 65




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« on: January 27, 2019, 09:03:04 PM »

Ok, first off I know we should only transmit with enough power to successfully be able to communicate without using more then we need.

Yet we are allowed to use up to 1500watts on VHF 2m bands.

The most I have ever seen  HT have is 10watts, the most in a mobile is 100watts.

I understand, that in a HT more power would mean shorter batter life and higher expense.

Even with mobiles there are vehicle restraints to some degree, then higher cost.

I have seen some VhF 2m amplifiers that can take a Radio to as much as 300 watts.

So am I to assume, no one ever transmits at 1500watts? That there just aren’t any vhf radios including repeaters that come anywhere close to transmitting and using that much power?

Please don’t assume that I am wanting more power in my radios or even feel the need to have that much power.

How much power does an AVERAGE repeater have?

How much power does it take to go any distance? Assume for that question, that there are no structures or trees or landscape blocking the antenna set at a height of 50’ and the only thing that would keep line of sight is curvature of the Earth. If that was the case, how much power does it take to go how far?

Does having more VHF power allow it to better punch its way through buildings and vegetation?
« Last Edit: January 27, 2019, 09:08:02 PM by KG9ZTX » Logged
G3RZP
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Posts: 1319




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« Reply #1 on: January 28, 2019, 03:35:48 AM »

Those sort of powers were used on EME when people were using CW, and also for DX work on CW on 2m such as Hawaii to California.  The newer digital modes allow the use of less power, but some contest stations used (and possibly still do) up to 1500 watts output on 2 and 70cm, with big antennas. The only time I've operated in a VHF/UHF contest, I was on 70cms with about 1kW out and was having a QSO rate of 30 an hour over paths around 600miles - until the generator failed! That was as a visitor to a station on a hilltop in Maine.....
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W9IQ
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Posts: 3534




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« Reply #2 on: January 28, 2019, 04:11:25 AM »

If there are no obstructions between them, two towers at 50 feet each will yield a reliable radio range of about 20 miles (32 km) on 2 meters. This of course assumes that both tower bases are at the same elevation.

If you place 1/4 wave ground plane antennas on the top of each 50 foot tower, use marginal coax cable to connect them to the transceivers, and use moderate quality transceivers, you will need less than 1 mW (0.001 watts) of power to communicate over the 20 mile path on 2 meters. If you could obtain a 100 mile line of sight path, you would only need about 20 milliwatts (0.02 watts) of power. Look up the Friis equation to learn more about this calculation.

Repeater output power (from the duplexer output) can run from 10 to 150 watts or more. Antenna system gain will typically raise this further. This "extra" power is to offset the effects of trees, buildings, terrain, rubber ducky antennas, etc.

High power amplifiers are typically used for simplex modes that involve reflected (e.g. atmosphere or moon) signals that are not simple line of sight communications.

- Glenn W9IQ

« Last Edit: January 28, 2019, 04:24:30 AM by W9IQ » Logged

- Glenn W9IQ

I never make a mistake. I thought I did once but I was wrong.
G8HQP
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Posts: 971




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« Reply #3 on: January 29, 2019, 06:40:40 AM »

At VHF frequencies the world roughly divides into two groups: those within your radio horizon (you can communicate with them using a few watts), those beyond your radio horizon (you can't communicate with them at all). This simple picture is not quite true, because there are also:
1. people just on your radio horizon - a bit more power might just reach them, but a lot more power won't get you much further
2. people you can reach via distant reflectors (e.g. the Moon, tropospheric forward scatter) - for these you need high power
However, these people need high power too otherwise you won't hear them. Hence the general rule that quite low power (by HF standards) is enough for most purposes for VHF.

HF is different because you have more attenuation, you are almost always using distant reflectors and you have more local noise at the receiving end.
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N8FVJ
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Posts: 910




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« Reply #4 on: January 29, 2019, 07:12:31 AM »

50 watts vs higher power on 2 meters can help under certain circumstances. The ham may have his beam antenna pointed in the wrong direction and cannot hear 50 watts. The band is noisy and the extra power gets you out of the noise at the fringe range. Tall buildings in a city may block a lower power signal, but I do not have that issue. For most communications within line of site, 25 to 50 watts is enough power on 2 meters SSB. I use 350 watts on 2 meters for a little extra power with a 8dB dual band beam antenna.

I have not performed the math, but perhaps a 14-16dB gain beam antenna with 50 watts equals a 350 watt signal into an 8dB beam antenna. I just do not care for extremely narrow beam antennas as I may miss a signal.

1500 watts out on 2 meters makes for a very expensive amplifier and tube such as an 8877 tube. I'll pass.
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AC2RY
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Posts: 756




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« Reply #5 on: January 29, 2019, 07:51:23 AM »


So am I to assume, no one ever transmits at 1500watts? That there just aren’t any vhf radios including repeaters that come anywhere close to transmitting and using that much power?

1.5kW is needed if you are serious about using tropospheric scatter for propagation beyond line of sight (up to several hundred miles). Though you likely need to go higher in frequencies all way to GHz to make higher gain antennas to augment high power.

This mode is commonly used for land based military communications.
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W4KYR
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« Reply #6 on: January 29, 2019, 08:22:00 AM »

I knew someone in Northern NJ that used a 160 watt amp and a 10 element antenna who regularly got out to New England on 2 meter SSB, he told that he used to have almost regular QSO's with someone in Rhode Island.
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W1VT
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Posts: 3397




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« Reply #7 on: January 29, 2019, 08:25:39 AM »

http://manitousys.com/home/products/communications-amplifiers/series-la-communications-amplifier/
Here is a company that makes 1500W 2M amplifiers.  I don't know how much product they sell.  I know the former owner/founder sold amps until he passed away.

https://qrznow.com/the-vhfuhf-dx-book-2017-replica-edition-is-now-available-for-free-download/
This book describes how to build and operate high power tube type amplifiers in great detail.
The UK limit is 400 watts, but really, there isn't all that much difference between 1500W and 400W aside from the cost of the tubes.

« Last Edit: January 29, 2019, 08:29:35 AM by W1VT » Logged
WB2WIK
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Posts: 21837




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« Reply #8 on: January 29, 2019, 11:02:13 AM »

A lot of moonbouncers still run 1500W output power.

My own 2m amplifier (homebrew dual 4CX250Bs) runs 1 kW CW output or about 800W PEP on SSB.

FM users rarely if ever run power close to that.   If "one" did, it would make him an "alligator" (big mouth, small ears) so lots of stations would hear him, but he wouldn't hear them unless they could also run that power level -- which would be very rare.

Most 2m repeaters run in the 50W - 100W output range.

Handheld rigs running more than about 7W output are rare due to battery limitations, but also due to heat dissipation limitations.   If the radio gets so hot you can't hold it comfortably, it's no longer realoly a "handheld." Cheesy
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KA4WJA
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Posts: 1098




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« Reply #9 on: January 29, 2019, 11:39:21 AM »

Gary,
Here is a pic of my 1200 watt 2m amp....the grey box on top of my Alpha 77...
It runs a pair of 8874's / 3CX400u's, and makes 1100 to 1200 watts, cleanly...on CW and SSB...and while could run 800 - 1000 watts intermittently on FM, it's rated for 400 watts continuous-duty for FM broadcast....

 
It's a Tempo 2002, from 1979, that I bought used in 1983 (for about the cost of the tubes, and I got a spare pair as well...)
It's 40 years old, and with original tubes still outputs 1100 - 1200 watts....and never a hick-up!

I used it on 2m EME (moonbounce), that's about a half-million miles, round trip!! and also on some long-haul 2m tropo-scatter work (800 - 900 miles)....and of course on a few 2m Es openings, and one GREAT evening of 1500 - 2000 mile F2 opening....and occasionally used it for just some local tropo work (300 - 400 miles)....I had 4 long-boom yagis on Az/El drive, at 50'....fed with 7/8" Heliax and tower-mounted GaSFET rec pre-amp (that I blew up twice, before I made a good sequencer!)



Now, as for your actual questions...

As some have noted, high-power "2m amplifiers" are a rare breed....but, not just because the need is small (just long-range troposcatter and moonbounce), but also because of the expense ($)...and the knowledge / care needed to design or build one...

{FYI, most modern ham repeaters are 25 to 50 watts, with some few wide-area-coverage repeaters (like mine) having 100 - 125 watts....and a few with extra long/lossy feedlines, might be 250 watts, that's about it....repeater coverage is all about antenna height (above average terrain), and sometimes about antenna patterns, but usually the transmit power never needs to be much more than any mobile radio attempting to use it...}

The origins of "high-power" VHF and UHF amateur radio amplifiers have their genesis in military surplus VHF gear, as well as some old "mobile phone" gear....this was in the 1950's, and the best most could do was a pair of 4x150a's and about 500 watts out, from military surplus VHF / UHF transmitters/amps....but most had only 100 - 250 watts from single tube amps....
Take note that some of these were actually Class C amps, so were just for CW....(or FM)

Some even used high-power "triplers" to get on 432mhz, from a 144mhz CW transmitter....and then added a 4x150a or even a 4cx250b PA stage...

Much of this was homebrew, with some modified military surplus VHF/UHF transmitters...

As things progressed the 4CX250b became readily available to hams (that means it was CHEAP!) and that meant that some hams designed and built single-tube amps with ~ 200 - 300 watts out....but they had issues with stability....so, even though this was always the place for only those with knowledge and experience, it was now an issue for even the best of the best, to make sure their VHF and UHF amps were not just high-power out-of-band oscillators!!

In the 1960's some "plumber's specials" and "strip-line" tank circuit designs were made, that allowed for a fairly stable high-power amplifier....
(and, around this same time, most non-amateur VHF/UHF systems were never more than a few hundred, to 500, watts...so, except for the BIG tubes and amps used for multi-kilowatt FM Radio Broadcast and VHF TV Broadcast, 500 to 600 watts was about all that could be done for most hams...)
So, a pair of 4cx250b's became the standard high power vhf and uhf amateur station's set-up...and from the 1960's thru the 1980's, this was "normal" high-power...

Now, please remember, that the FCC rules back then only permitted 1000 watts DC plate input power (there was no output power rule, back then), and as such typical max "legal" output was about 600 watts...
So, that's what most high-power stations had!

 

Then in the late 60's, there was a "relatively" affordable new tube, from Eimac....the 3cx1500 / 8877...which was capable of 2000+ watts output thru 250mhz, and actually worked well thru 450mhz (producing 1500-1700 watts out, at 432mhz, if you had an adequate power supply)

But, who had one of those new tubes??
Well, the answer was Bob Southerland, W6SAI (later, W6PO)....Bob worked for Eimac...
And, in the late 60's he designed a vhf amplifier (and a uhf amplifier) using this new tube...

He wrote of his amp, including schematic, and construction details in 1971....and the ham community now had a somewhat affordable, higher-power tube / amplifier....and it was wonderfully stable, very clean, and high-gain as well....
{and, btw, almost 50 years later, is still considered to be THE definitive 2m high-power amp!}

http://www.w5un.net/8877-1.htm








But, FCC rules still wouldn't allow more than 1000 watts DC input, so that meant that if you built an 8877 amp, you just said "I'm running an 8877"  or "I'm running a W6PO amp"....and everyone knew you were running 1500 - 2500 watts out....
NOBODY ever had an issue with that, ever....mostly because nobody ever heard these guys, unless you had an array pointed at the moon, as this was almost the exclusive use of this amp, 2m moonbounce!!  (most of those on 432mhz moonbounce were still using a pair of 4cx250b's...but a few did manage to build a 432mhz 8877 amp...and as the 8938 tube became available, 2000 watts on 432mhz was possible...)


Also in the early 1970's the "strip-line" design got a face-lift of sorts, with the K2RIW design....  
Started as a improvement of a UHF strip-line design, Dick, K2RIW designed what is still considered to be the best "small form" mid-power UHF and VHF amp!

http://www.g4ohv.com/k2riw.html

http://www.newsvhf.com/2m_stripline.pdf

{BTW, in college (1981?) myself and classmate built a K2RIW 432mhz amp, for a NE contest station...and we got a big power supply from the EE building, and it ran 800 watts out!!  And, I think it was stil running 20 years later....}


In the 1970's Pliumber's Specials tank circuits (where actual copper plumbing pipe is used as part of the tank circuit) were also very popular, especially for those desiring a "easier" construction project, or for "mass production"...
Yep, there were a few hams that made amps for others....and they were wonderful!
But, as of yet, there were still no real "high-power" (600 - 2000 watt) ham radio VHF / UHF amps made in "production"...(except for a few 6m amps??  and a few "mid-power" amps)
Well, that changed with Henry Radio...

Henry Radio (in California) rolled out their "2000" series of amps, using a pair of 8874's (the little brother of the big 8877)...
The "Tempo 2002" was 2m...the "Tempo 2006" was for 6m....and while I never saw one, the "Tempo 2004" was for 432mhz.... (and they also made a "Tempo 6 n 2" which did both 2m and 6m)
These all have a huge / heavy-duty power supply, and run a pair of the high-gain, and very stable 8874's in grounded-grid, in a plumber's special design...
They make 1100 to 1200 watts out (with 40 to 60 watts of drive)...

Here is the pic of mine....



In the mid / late 1980's Henry Radio came out with their "3000 series"....the 3002, 3004, and 3006....these were their stand-alone console amps from 2m, 6m, and 432mhz, using the 8877 and a big power supply (and I think the W6PO design)...
I had a friend that had the 3002, and driving it with 80 watts, he had about 1900 - 2000 watts out...
The darn things were big and heavy....and expensive (~ $3500 in 1980's dollars)

{BTW, the FCC also changed the rules to "1500 watts out PEP" for all modes...so, that made those running big amps on 2m amd 432mhz, legal...well, almost "legal", 'cuz nobody runs an 8877 on 2m moonbounce at only 1500 watts, unless they're power supply-limited!! }

Here is a pic...



In the 1990's Henry changed the old 2002, 2004, and 2006...to the 2002a, 2004a, and 2006a....when they changed from a pair of 8874's to a single 3cx800....
The 3cx800 had higher gain, and made construction/production easier, but...
But a pair of 8874's are more rugged than a single 3cx800, and there were some with tube failures, so Henry upgraded them (sold 'em) to the 3000 series amps....
The 2002a is a good amp, and will do all the original 2002 will do, but the 2002a is a bit more "dainty" and you need to be careful on that tube, so most will only drive 'em to 800 - 1000 watts out, so they get many years of service from them
{BTW, on a side note, my 2002 still makes 1100 to 1200 watts out, on ORGINAL 40 year old 8874's!!...only work I've ever done (other than cleaning it) was to replace the HV caps and rectifier sticks....and it keeps on purring along!}
 

Over the years, there have been others making very small quantities of 2m high-power amps...usually built-to-order, and not shipped right off-the-shelf....such as Lunar Link's amps...


You'll notice that none of the above are solid state??
The answer to why, up until the past 5 years or so has been that were not any real high-power solid-state devices that were affordable.....and for the most part, compared to tubes, that IS still true!!

But, with the introduction of reasonably-priced high-power LDMOS devices, some have tried to make 1Kw to 1200 watt 2m amps....but they haven't been successful...
Now, some here will quibble with that statement, saying that some were made....yep, that's true, but none were successful!!
Mainly due to "cost" / complexity, as well as heat dissipation, etc...BUT...

But, fact is the IMD of them was really bad....and while the FCC doesn't care about ham radio IMD, most of these 2m 1200 watts LDMOS amps couldn't pass FCC certification (part 15, etc.) nor harmonic regs....
{Two of my best friends did the FCC cert testing for some of them....and they were horrified by the crappy results, and crappy design/build....they found 3rd order IMD of only -18 to -20db(PEP)....and some harmonics were only 35 - 40 db down....true "CB Radio-type" performance...}

Of course, you could design and build a SS high-power 2m amp (whether MOSFET or LDMOS) that would be good (and clean), but so far nobody has one on the market....



Now, Gary, I do hope I cleared up the "mystery" of 2m amps??

As for "how much power does it take?"...well, as you can see, for most 2m communications 10 watts to 50 watts is all that is needed...with some needing 100 - 150 watts...
But, only a few (working long-haul tropo-scatter, or some still doing meteor-scatter, or the few doing moonbounce) using CW (or some SSB) have any need at all for any power over that....and as you can see, for moonbounce (CW) there's almost no such thing as "too much power"...  Smiley

{BTW, I personally don't consider computer-only-decoding modes (or computer-to-computer-only modes) to be actual real hams making contact....in my opinion it is computers making contact, not the human.....so, I haven't included any of the "negative signal-to-noise-ratio" / computer modes, like JT-65, JT-9, FT-8, etc., into any of my comments above....just CW, SSB (and FM)....'cuz if a human can't hear it, then a human isn't actually making that contact....just my opinion, so don't shoot me!}


73,
John,  KA4WJA
« Last Edit: January 29, 2019, 11:42:59 AM by KA4WJA » Logged
KA4WJA
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Posts: 1098




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« Reply #10 on: January 29, 2019, 12:53:18 PM »

BTW, I left out mention of the Dentron Clipperton V and the Gonset 903, 'cuz they're being discussed in the other thread here...
https://www.eham.net/ehamforum/smf/index.php/topic,1234.msg1111116.html#new

73,
John,   KA4WJA
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G3RZP
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Posts: 1319




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« Reply #11 on: January 29, 2019, 02:00:08 PM »

Another area we haven't mentioned is Meteor Scatter and Auroral reflection where QRO helps. VHF and UHF isn't just the local repeater and the local area: there are a number of other propagation modes used to work DX, some of which have very high path losses, necessitating high transmit power and high gain antennas.
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K0UA
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Posts: 4802




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« Reply #12 on: January 29, 2019, 02:02:42 PM »

Quote
{BTW, I personally don't consider computer-only-decoding modes (or computer-to-computer-only modes) to be actual real hams making contact....in my opinion it is computers making contact, not the human.....so, I haven't included any of the "negative signal-to-noise-ratio" / computer modes, like JT-65, JT-9, FT-8, etc., into any of my comments above....just CW, SSB (and FM)....'cuz if a human can't hear it, then a human isn't actually making that contact....just my opinion, so don't shoot me!}

Newsflash.  If you want to work meteor scatter, you WILL be working MSK144.  No one tries to work CW or SSB meteor scatter any more.  Thank God.  And while you can make meteor scatter contacts on 6 meter with 100 watts, more is much much better.  I made 25 states on MSK144, but it is all about high gain beam, and amps.  You may not consider it a contact, and you are free to think whatever you like, but IT IS.  I don't have a whole lot of interest in the mode any more as I have worked 48 states on 6 meters, some on MSK144 some on E skip, but I am not going to work Alaska or Hawaii on meteor scatter as it is not possible on that mode.

Besides people used all sorts of electronic methods back when people used to use CW.  They sent CW at super high speeds, and then tried to record it on the recieveing end and slow the tape down. A real Kludge, but I guess it sort of worked.  When MSK144 came along it was a revelation and game changer.  Time marches on, techniques improve. This is called advancing the state of the art.
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73  James K0UA
ARRL Missouri Technical Specialist
W6RZ
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Posts: 365




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« Reply #13 on: January 29, 2019, 03:07:02 PM »

Those sort of powers were used on EME when people were using CW, and also for DX work on CW on 2m such as Hawaii to California.

The Hawaii to California duct doesn't require high power. I've worked it on SSB from Silicon Valley with 100 watts to a big 2m yagi. Here's my terrain profile in that direction.

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KB1GMX
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Posts: 1824




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« Reply #14 on: January 29, 2019, 03:46:41 PM »

At 100W I can work Eastern MA to NJ on 2M SSB and with 50W in the mobile to
a good repeater as far as the terrain allows typically 40 to 90 miles.

You need two things a path and propagation.  If you have only one of those its
a maybe and both "usually mostly" if its near the horizon or there is obstacles.

I used to work AO27 (and others) with a pair of HTs one for UHF RX and the
other VHF TX and the VHF was a whopping 1.5W (yes one point 5).  If memory
serves the orbit of AO27 was about 480 miles and when on the horizon it would
be something over 2000 miles from me.  But nothing in the way except air.

Distance at RF is at best unlimited and at worst hard to get across the street.

Allison
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