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LDMOS for QRO

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Edward R Cole

LDMOS for QRO

Joe,

You are correct that the specs are for pulse and one can run CW/JT65
at this level since there is no IMD produced by a single sine
wave. So combining two running 750w each gets you 1500w in linear
operation with 2400w dissipation.

1500w mobile!!! Are you serious? I'd guess 200-250w would be
adequate for mobile. But I do not do serious HF'ing.

Your issue with heat sinks and copper spreaders is already solved and
one can run simple fans instead of blowers. And combining two
devices is more complicated than combining 8 or 16? Huh? If you
think this is all theoretical you are mistaken as these are out there
as kits and assembled amps on VHF to 1296. Several companies have
them for sale (M2 is one). The kits come with the LDMOS already
installed on a copper spreader designed for the needed heat
conduction. They haven't hit the HF market as yet but no reason why
not (be interesting to re-examine this topic in dec. 2015).

I sure would consider a 50v PS a lot simpler and safer than a 4kV
PS. In fact I have one that I bought on e-bay for $31 made by HP (it
will run my 1100w 6m PA). I also have a HB 4kV - 1.5A PS for my
8877...cost me a lot more than $31.

Once I use up my current 8877, I will likely sell my amp with the
final 8877 "pull" that I have in hand and replace it with a LDMOS amp
since I can install it next to the base off my tower instead of
having it inside with all the noise and HV. Then I can haul the
1-5/8 inch Hardline to the metal recycle'r as I will only need to run
RG213 to the amp with 4w. Yes, 240vac will be needed but running
that is not rocket science as every home well pump is wired with buried 240vac.

73, Ed - KL7UW

From: "Joe Subich, W4TV" <[hidden email]>
To: [hidden email]
Subject: Re: [Elecraft] (no subject)
Message-ID: <[hidden email]>
Content-Type: text/plain; charset=utf-8; format=flowed

> But no longer do you need to run a dozen "pills" (man I hate that
> term). Here is all you need for 1250w 1.8-600 MHz:

Unfortunately, the LDMOS device data sheets provide *no* IMD spec's
for linear operation. The only data is for CW and pulse service. If
one is to extrapolate from similar LDMOS devices (single FET vs. two
FETs on a common die), one would need to derate to 800-900 W PEP in
order to achieve reasonable IMD levels. That conclusion is further
corroborated by the compression spec's (actual vs. ideal output power)
which show the onset of output compression above 59 to 60 dBm (59 dBm
=> ~800W).

The devices work at 1200 W CW (or JT65) because those modes are single
tone and work with saturated operation (class C amplifiers) where IMD
performance is not "tested".

At full output these devices would be as dirty in SSB operation as the
old FM "brick" amplifiers were when run in SSB service - perhaps like
the RMA Italia solid state amps <G>.

BTW, since these are 50V parts they are not suited for mobile use at
12V (13.8 V nominal) service.

> $241.50 compared with the new price of a 8877 is pretty cheap!

To even approach the IMD performance and reliability of an 8877 you
would need two devices and the cooling problems (cost of heat sinks,
heat spreaders, etc.) are much more difficult with two of these devices
than with a single 8877. Any cost advantage for even two of the LDMOS
devices over an 8877 will be more than offset by cooling system (in
addition to splitter/combiner and protection system) costs.

73,

... Joe, W4TV

73, Ed - KL7UW
http://www.kl7uw.com
"Kits made by KL7UW"
Dubus Mag business:
[hidden email]

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Wes (N7WS)

Re: LDMOS for QRO

On 12/14/2014 2:10 AM, Edward R Cole wrote:
>
> 1500w mobile!!! Are you serious? I'd guess 200-250w would be adequate for
> mobile. But I do not do serious HF'ing.
>
When you get serious, here's how to do it. My Elmer, W7UVR, ran a high level
modulated 4-1000A mobile in the 1950s. Later went to SSB and a 15KW generator in
a bigger trailer. The one in the photo (trailer) was "only" 5KW. The whip
antennas had motor-tuned matching networks with vacuum variables and edge-wound
inductors. The beam was later replaced with a tribander, diced up with machined
tubular hinges built by a tool-maker ham friend.

http://www.k0bg.com/gallery2/main.php?g2_itemId=1039

http://www.k0bg.com/gallery2/main.php?g2_itemId=1042

http://www.k0bg.com/gallery2/main.php?g2_itemId=1045

Wes N7WS
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Joe Subich, W4TV-4

Re: LDMOS for QRO

In reply to this post by Edward R Cole

> Your issue with heat sinks and copper spreaders is already solved
> and one can run simple fans instead of blowers. And combining two
> devices is more complicated than combining 8 or 16? Huh?

I'm not saying it isn't possible - nor that is hasn't been solved.
Only that is it not less expensive than an 8877 and that those who
say a single 1.25 KW LDMOS is a suitable replacement for an 8877
are not considering other performance issues like IMD, etc.

The multiple module with combiner configurations have been around for
a long time. The LDMOS modules were designed for television broadcast
service in addition to ISM purposes. The broadcaster transmitters use
a large number of combined modules to reach quite high power levels
but each module is running less than 1 KW and the transmitters have
significant amounts of adaptive precorrection to maintain linearity.

If you want to step back and design precorrection capability into
the transceiver DSP (e.g., an input for a directional coupler/RF
tap at the output of the *system*) and can maintain linearity of
multiple modules "close enough" to use a single composite correction,
be my guest. However, the cost and complexity are an order of
magnitude greater than a good cathode driven triode - but then if
you add phase modulation to the precorrection, perhaps you can get
away saturated (pulse) amplifiers.

73,

... Joe, W4TV

On 2014-12-14 4:10 AM, Edward R Cole wrote:

> Joe,
>
> You are correct that the specs are for pulse and one can run CW/JT65 at
> this level since there is no IMD produced by a single sine wave. So
> combining two running 750w each gets you 1500w in linear operation with
> 2400w dissipation.
>
> 1500w mobile!!! Are you serious? I'd guess 200-250w would be adequate
> for mobile. But I do not do serious HF'ing.
>
> Your issue with heat sinks and copper spreaders is already solved and
> one can run simple fans instead of blowers. And combining two devices
> is more complicated than combining 8 or 16? Huh? If you think this is
> all theoretical you are mistaken as these are out there as kits and
> assembled amps on VHF to 1296. Several companies have them for sale (M2
> is one). The kits come with the LDMOS already installed on a copper
> spreader designed for the needed heat conduction. They haven't hit the
> HF market as yet but no reason why not (be interesting to re-examine
> this topic in dec. 2015).
>
> I sure would consider a 50v PS a lot simpler and safer than a 4kV PS.
> In fact I have one that I bought on e-bay for $31 made by HP (it will
> run my 1100w 6m PA). I also have a HB 4kV - 1.5A PS for my 8877...cost
> me a lot more than $31.
>
> Once I use up my current 8877, I will likely sell my amp with the final
> 8877 "pull" that I have in hand and replace it with a LDMOS amp since I
> can install it next to the base off my tower instead of having it inside
> with all the noise and HV. Then I can haul the 1-5/8 inch Hardline to
> the metal recycle'r as I will only need to run RG213 to the amp with
> 4w. Yes, 240vac will be needed but running that is not rocket science
> as every home well pump is wired with buried 240vac.
>
> 73, Ed - KL7UW
>
> From: "Joe Subich, W4TV" <[hidden email]>
> To: [hidden email]
> Subject: Re: [Elecraft] (no subject)
> Message-ID: <[hidden email]>
> Content-Type: text/plain; charset=utf-8; format=flowed
>
>
> > But no longer do you need to run a dozen "pills" (man I hate that
> > term). Here is all you need for 1250w 1.8-600 MHz:
>
> Unfortunately, the LDMOS device data sheets provide *no* IMD spec's
> for linear operation. The only data is for CW and pulse service. If
> one is to extrapolate from similar LDMOS devices (single FET vs. two
> FETs on a common die), one would need to derate to 800-900 W PEP in
> order to achieve reasonable IMD levels. That conclusion is further
> corroborated by the compression spec's (actual vs. ideal output power)
> which show the onset of output compression above 59 to 60 dBm (59 dBm
> => ~800W).
>
> The devices work at 1200 W CW (or JT65) because those modes are single
> tone and work with saturated operation (class C amplifiers) where IMD
> performance is not "tested".
>
> At full output these devices would be as dirty in SSB operation as the
> old FM "brick" amplifiers were when run in SSB service - perhaps like
> the RMA Italia solid state amps <G>.
>
> BTW, since these are 50V parts they are not suited for mobile use at
> 12V (13.8 V nominal) service.
>
> > $241.50 compared with the new price of a 8877 is pretty cheap!
>
> To even approach the IMD performance and reliability of an 8877 you
> would need two devices and the cooling problems (cost of heat sinks,
> heat spreaders, etc.) are much more difficult with two of these devices
> than with a single 8877. Any cost advantage for even two of the LDMOS
> devices over an 8877 will be more than offset by cooling system (in
> addition to splitter/combiner and protection system) costs.
>
> 73,
>
> ... Joe, W4TV
>
>
> 73, Ed - KL7UW
> http://www.kl7uw.com
> "Kits made by KL7UW"
> Dubus Mag business:
> [hidden email]
>
> ______________________________________________________________
> Elecraft mailing list
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>

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Kevin Stover

Re: LDMOS for QRO

In reply to this post by Edward R Cole

W6PQL has designed and built a 1KW SSPA for 1.8-54MHz using an LDMOS
device. Freescale I think.
he has also designed a pretty stout Low Pass filter designed for 1.5KW
1.8-54 MHz.
He can get 1.2KW out of it at saturation with 2-3 W drive.
A pair of these devices @ 750W could do 1500W all day any mode. but then
the power supply becomes the limiting factor.. 50V at 70amps?

http://www.w6pql.com/1_kw_sspa_for_1_8-54_mhz.htm

--
R. Kevin Stover
AC0H
ARRL
FISTS #11993
SKCC #215
NAQCC #3441

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Myron WVØH

Re: LDMOS for QRO

Soon GaN will hold possibilities.

Myron WVØH
Printed on Recycled Data

> On Dec 14, 2014, at 8:41 AM, Kevin Stover <[hidden email]> wrote:
>
> W6PQL has designed and built a 1KW SSPA for 1.8-54MHz using an LDMOS device. Freescale I think.
> he has also designed a pretty stout Low Pass filter designed for 1.5KW 1.8-54 MHz.
> He can get 1.2KW out of it at saturation with 2-3 W drive.
> A pair of these devices @ 750W could do 1500W all day any mode. but then the power supply becomes the limiting factor.. 50V at 70amps?
>
> http://www.w6pql.com/1_kw_sspa_for_1_8-54_mhz.htm
>
> --
> R. Kevin Stover
> AC0H
> ARRL
> FISTS #11993
> SKCC #215
> NAQCC #3441
>
> ______________________________________________________________
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Ignacy

Re: LDMOS for QRO

In reply to this post by Kevin Stover

Kevin Stover wrote

W6PQL ....
A pair of these devices @ 750W could do 1500W all day any mode. but then
the power supply becomes the limiting factor.. 50V at 70amps?

Expert 2k-fa uses a commercial 50v 60A (more peak) PS that weights perhaps 5 lb and is pretty small. Costs $500 in single quantities. Running 1.5KW in contests, the Expert heats the room much less than TT Centurion.

For 2m SSB the Freescale device has decent IMD at 900W (and 50% efficiency) and indecent IMD but some 70% efficiency at 1.3 KW. With pre distortion (which every SDR will have soon) perhaps one can get IMD of -50 db at 1.3 KW. At HF the issue is of multi band efficient matching.

Ignacy, NO9E

David Cutter

Re: LDMOS for QRO [OT]

In reply to this post by Kevin Stover

I'm a little surprised that folks in this group haven't suggested liquid
cooling for this modest application. Semiconductor cold plates have been
around for a long time, are economical to use and in my view a much better
solution than forced air cooling. They are compact, quiet, require far less
cabinet space, keep junctions cooler and more stable than air could ever and
enable higher reliability.

Look at Aavid for instance, whose devices I used on many occasions:
http://www.aavid.com/sites/default/files/products/liquid/pdf/liquid-cold-plate-datasheet-hicontact.pdf

If you play your cards right, you can cool the amplifier and the power
supply on a short 4-pass plate. Put the heat somewhere convenient, not in
your shack.

73

David
G3UNA

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Elecraft mailing list

Re: LDMOS for QRO [OT]

Good point David,
I have seen an industrial RF amplifier heat sink made out of a 1/4 " copper plate married to a aluminum water cooled plate. Ran on a simple 120 VAC pump to a 5 gal tank, like my 5KW Bird water cooled dummy load that uses a total water waste system does the same dissipation. As I remember, many years ago, it was rated at removing 5KW of heat. I know should have the BTU but I don't remember.
Mel, K6KBE

From: David Cutter <[hidden email]>
To: [hidden email]
Sent: Sunday, December 14, 2014 3:32 PM
Subject: Re: [Elecraft] LDMOS for QRO [OT]

I'm a little surprised that folks in this group haven't suggested liquid
cooling for this modest application. Semiconductor cold plates have been
around for a long time, are economical to use and in my view a much better
solution than forced air cooling. They are compact, quiet, require far less
cabinet space, keep junctions cooler and more stable than air could ever and
enable higher reliability.

Look at Aavid for instance, whose devices I used on many occasions:
http://www.aavid.com/sites/default/files/products/liquid/pdf/liquid-cold-plate-datasheet-hicontact.pdf

If you play your cards right, you can cool the amplifier and the power
supply on a short 4-pass plate. Put the heat somewhere convenient, not in
your shack.

73

David
G3UNA

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Nick Kemp

Re: LDMOS for QRO [OT]

There are 3,413 btu per KW HR consumed.

Mel Farrer via Elecraft wrote...I know should have the BTU but I don't
remember.

Nick N1KMP
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Elecraft mailing list

Re: LDMOS for QRO [OT]

In reply to this post by Elecraft mailing list

Water cooling is OK for QRP. A friend of mine was building a "special" contest amplifier. He was working out the cooling which presented a problem because of the heat involved. I suggested using an upright type freezer and put amp in the freezer, It worked great!!
George, fritkin

On Sunday, December 14, 2014 3:55 PM, Mel Farrer via Elecraft <[hidden email]> wrote:

Good point David,
I have seen an industrial RF amplifier heat sink made out of a 1/4 " copper plate married to a aluminum water cooled plate. Ran on a simple 120 VAC pump to a 5 gal tank, like my 5KW Bird water cooled dummy load that uses a total water waste system does the same dissipation. As I remember, many years ago, it was rated at removing 5KW of heat. I know should have the BTU but I don't remember.
Mel, K6KBE

From: David Cutter <[hidden email]>
To: [hidden email]
Sent: Sunday, December 14, 2014 3:32 PM
Subject: Re: [Elecraft] LDMOS for QRO [OT]

I'm a little surprised that folks in this group haven't suggested liquid
cooling for this modest application. Semiconductor cold plates have been
around for a long time, are economical to use and in my view a much better
solution than forced air cooling. They are compact, quiet, require far less
cabinet space, keep junctions cooler and more stable than air could ever and
enable higher reliability.

Look at Aavid for instance, whose devices I used on many occasions:
http://www.aavid.com/sites/default/files/products/liquid/pdf/liquid-cold-plate-datasheet-hicontact.pdf

If you play your cards right, you can cool the amplifier and the power
supply on a short 4-pass plate. Put the heat somewhere convenient, not in
your shack.

73

David
G3UNA

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Edward R Cole

Re: LDMOS for QRO

In reply to this post by Edward R Cole

OK. My reason for mentioning these amps was to answer some of the
negative points being made in regard to a fictitious KPA1500. These
days one does not have to combine a lot of lower power FETs to reach
QRO. I gave you a link to the device which is made by
Freescale. There are comparable devices made by NXP.

I replied to the argument that one can not run them linear at
1200w. To quote myself: "So combining two running 750w each gets you
1500w in linear operation with 2400w dissipation." Most RF
transistors will not be linear if driven into saturation so one backs
off on the drive and resultant output to improve linearity.

Heat dissipation is taken care of by using copper heat spreaders
under the transistors coming from all these suppliers unless you buy
the LDMOS directly (W6PQL uses a 3x5x1/2 inch copper spreader). I
would suggest either the amp kits or buying assembled amp pallets to
build with.

Price: two LDMOS would run roughly $500. I new 8877 from RFParts is
$1450 (Eimac) or $665 (Taylor). Of course you can purchase a used
8877 in the $350-450 range. The HVPS will run about $500 and you
probably would have another $400 in materials to complete a basic HF
amp with manual tuning (total= $2350 (Eimac) to $1250 (used 8877)).

W6PQL is offering an assembled single LDMOS amp for $825 so two would
run $1650 and probably another $400 to make a complete 1500w SSB HF
amp. Surplus HP Blade 50v -50A PS run $30-50 on e-bay. To run two
LDMOS you just have two 50vv PS supplying each separately. Total= $2150.

If you build your own you can save a little off this total - W6PQL
kit is $563 which includes the NXP BLF-188XR.
http://www.w6pql.com/parts_i_can_provide.htm est. total
2x$563+$400+$100 = $1625

No point belaboring this as there are going to be some amps showing
up this coming year using these LDMOS devices.

-----------------
From: Kevin Stover <[hidden email]>
To: [hidden email]
Subject: Re: [Elecraft] LDMOS for QRO
Message-ID: <[hidden email]>
Content-Type: text/plain; charset=ISO-8859-1; format=flowed

W6PQL has designed and built a 1KW SSPA for 1.8-54MHz using an LDMOS
device. Freescale I think.
he has also designed a pretty stout Low Pass filter designed for 1.5KW
1.8-54 MHz.
He can get 1.2KW out of it at saturation with 2-3 W drive.
A pair of these devices @ 750W could do 1500W all day any mode. but then
the power supply becomes the limiting factor.. 50V at 70amps?

http://www.w6pql.com/1_kw_sspa_for_1_8-54_mhz.htm

73, Ed - KL7UW
http://www.kl7uw.com
"Kits made by KL7UW"
Dubus Mag business:
[hidden email]

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David Woolley (E.L)

Re: LDMOS for QRO

In reply to this post by Edward R Cole

Neither morse (loosely called CW), nor JT65, are pure sine waves, so
they will have IMD, although it may well be less than the key clicks (as
conventionally understood for morse, and because of the abrupt frequency
changes in JT65). True CW cannot convey any more information than its
existence.

Measured in a 1Hz bandwidth, the JT65 IMD would be very low, and
measured in the total bandwidth, it would be concentrated, in time,
around signalling unit boundaries. Similarly for the "clicks".

As to the mobile powers, I would have thought that it would be unsafe to
operate at some of the power levels mentioned, both in terms of the risk
to other people (e.g. someone in an open, or soft, top vehicle, or even
pedestrians in slow moving traffic), and the risk of causing an accident
as as result of EMC failures in passing vehicles.

--
David Woolley
Owner K2 06123

On 14/12/14 09:10, Edward R Cole wrote:
>
> You are correct that the specs are for pulse and one can run CW/JT65 at
> this level since there is no IMD produced by a single sine wave. So
> combining two running 750w each gets you 1500w in linear operation with
> 2400w dissipation.
>
> 1500w mobile!!! Are you serious? I'd guess 200-250w would be adequate
> for mobile. But I do not do serious HF'ing.

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W1KSZ

Re: LDMOS for QRO [OT]

In reply to this post by David Cutter

I did a random selection of 3 of their alleged distributors and found
nothing on
their sites.

Too bad, they look like they could be useful. Guess I'll ping them
directly and see
what I get.

73 es HH, Dick, W1KSZ

On 12/14/2014 4:32 PM, David Cutter wrote:

> I'm a little surprised that folks in this group haven't suggested
> liquid cooling for this modest application. Semiconductor cold plates
> have been around for a long time, are economical to use and in my view
> a much better solution than forced air cooling. They are compact,
> quiet, require far less cabinet space, keep junctions cooler and more
> stable than air could ever and enable higher reliability.
>
> Look at Aavid for instance, whose devices I used on many occasions:
> http://www.aavid.com/sites/default/files/products/liquid/pdf/liquid-cold-plate-datasheet-hicontact.pdf
>
>
> If you play your cards right, you can cool the amplifier and the power
> supply on a short 4-pass plate. Put the heat somewhere convenient,
> not in your shack.
>
> 73
>
> David
> G3UNA
>
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
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Gerry Hull

Re: LDMOS for QRO [OT]

In reply to this post by David Cutter

Here's a 144MHz 1.5Kw water-cooled LDMOS amplifier putting out full power
in a June VHF contest, with me operating at W2SZ/1.
It was a cloudy day, and the amp was so cool, in fact, we were worried
about condensation. Look at the size! The power supply is a 50v/50a
surplus PC supply off of ebay.
The amp was built by Brian Justin, WA1ZMS.

I have found cold plates on the surplus market. Every once in a while,
Electronic Surplus Sales in Manchester, NH has em.

Amp in Action:

https://www.youtube.com/watch?v=vegBv6ddAUA

73

Gerry Hull, W1VE | Hancock, NH USA
AKA: VE1RM | VY2CDX | VO1CDX | 6Y6C | 8P9RM
<http://www.yccc.org> <http://www.yccc.org/>
<http://www.facebook.com/gerryhull>
<https://plus.google.com/+GerryHull/posts> <http://www.twitter.com/w1ve>

On Sun, Dec 14, 2014 at 6:32 PM, David Cutter <[hidden email]> wrote:

>
> I'm a little surprised that folks in this group haven't suggested liquid
> cooling for this modest application. Semiconductor cold plates have been
> around for a long time, are economical to use and in my view a much better
> solution than forced air cooling. They are compact, quiet, require far
> less cabinet space, keep junctions cooler and more stable than air could
> ever and enable higher reliability.
>
> Look at Aavid for instance, whose devices I used on many occasions:
> http://www.aavid.com/sites/default/files/products/liquid/
> pdf/liquid-cold-plate-datasheet-hicontact.pdf
>
> If you play your cards right, you can cool the amplifier and the power
> supply on a short 4-pass plate. Put the heat somewhere convenient, not in
> your shack.
>
> 73
>
> David
> G3UNA
>
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
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>
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> Message delivered to [hidden email]
>

David Cutter

Re: LDMOS for QRO [OT]

Thanks for showing us that, Gerry, be nice to see more of the water works. Do you have any pics of the build?

David
G3UNA
----- Original Message -----
From: Gerry Hull
To: David Cutter
Cc: Reflector Elecraft
Sent: Tuesday, December 16, 2014 3:19 AM
Subject: Re: [Elecraft] LDMOS for QRO [OT]

Here's a 144MHz 1.5Kw water-cooled LDMOS amplifier putting out full power in a June VHF contest, with me operating at W2SZ/1.
It was a cloudy day, and the amp was so cool, in fact, we were worried about condensation. Look at the size! The power supply is a 50v/50a surplus PC supply off of ebay.
The amp was built by Brian Justin, WA1ZMS.

I have found cold plates on the surplus market. Every once in a while, Electronic Surplus Sales in Manchester, NH has em.

Amp in Action:

https://www.youtube.com/watch?v=vegBv6ddAUA

73

Gerry Hull, W1VE | Hancock, NH USA

On Sun, Dec 14, 2014 at 6:32 PM, David Cutter <[hidden email]> wrote:
I'm a little surprised that folks in this group haven't suggested liquid cooling for this modest application. Semiconductor cold plates have been around for a long time, are economical to use and in my view a much better solution than forced air cooling. They are compact, quiet, require far less cabinet space, keep junctions cooler and more stable than air could ever and enable higher reliability.

Look at Aavid for instance, whose devices I used on many occasions:
http://www.aavid.com/sites/default/files/products/liquid/pdf/liquid-cold-plate-datasheet-hicontact.pdf

If you play your cards right, you can cool the amplifier and the power supply on a short 4-pass plate. Put the heat somewhere convenient, not in your shack.

73

David
G3UNA

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Dave-3

Re: LDMOS for QRO

In reply to this post by Edward R Cole

Hopefully the manufacturers will produce GAN devices that operate that low
in frequency. Currently available ones do 3GHz and above. I have one
producing 50W at 10Ghz and another 70W at 3.4GHz neither will even go down
to 1.2GHz

Dave
G4FRE

Date: Sun, 14 Dec 2014 08:53:24 -0700
From: Myron WV?H <[hidden email]>
To: Kevin Stover <[hidden email]>
Cc: "[hidden email]" <[hidden email]>
Subject: Re: [Elecraft] LDMOS for QRO
Message-ID: <[hidden email]>
Content-Type: text/plain; charset=utf-8

Soon GaN will hold possibilities.

Myron WV?H
Printed on Recycled Data

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W1KSZ

Re: LDMOS for QRO [OT]

In reply to this post by David Cutter

If one wanted to use one of these to cool an LDMOS VHF KW, where would
one find the design info to calculate which cold plate would provide
sufficient
cooling ?

I envision a stack something like this:

LDMOS PC Board
Copper Heatsink (thickness need be determined)
Cold Plate
Aluminum Heat Sink (is this really necessary ?).

73 es HH, Dick, W1KSZ

On 12/14/2014 4:32 PM, David Cutter wrote:

Wes (N7WS)

Re: LDMOS for QRO [OT]

Unless you want to run fresh water down the drain (in Arizona we don't do this)
you have to get the heat into the air someplace. I'm not sure that running
water lines to outside air is much easier than getting coax through a concrete wall.

Speaking of difficult, the U.S. Navy AIM-54A Phoenix Missile which with I was
intimately familiar, used oil (Coolanol) cooling. Chassis were mounted on cold
plates and the vacuum tube modulator and pulse transformer were immersed in oil
and it also circulated through the PA klystron. Lines ran from the missile
umbilical to the wing or belly mounted launchers then to the F4 aircraft where a
conditioning unit resided. The stuff was insidious to work with. I ruined lots
of clothes, And it was hygroscopic, just the thing to use on a ship-borne system.

Wes N7WS

>
> On 12/14/2014 4:32 PM, David Cutter wrote:
>> I'm a little surprised that folks in this group haven't suggested liquid
>> cooling for this modest application. Semiconductor cold plates have been
>> around for a long time, are economical to use and in my view a much better
>> solution than forced air cooling. They are compact, quiet, require far less
>> cabinet space, keep junctions cooler and more stable than air could ever and
>> enable higher reliability.
>>
>> Look at Aavid for instance, whose devices I used on many occasions:
>> http://www.aavid.com/sites/default/files/products/liquid/pdf/liquid-cold-plate-datasheet-hicontact.pdf
>>
>>
>> If you play your cards right, you can cool the amplifier and the power supply
>> on a short 4-pass plate. Put the heat somewhere convenient, not in your shack.
>>
>> 73
>>
>> David
>> G3UNA
>>
>

David Cutter

Re: LDMOS for QRO [OT]

In reply to this post by W1KSZ

Hi Dick

Start from the LDMOS data sheet and work out the temperature you wish to
keep within at the junction. Because water cooling is so good, you can
choose either to run the device cooler than you would with air cooling to
improve reliability, or stick to the same temperature and get more power /
use a smaller cooling plate / use less water. There's a direct relationship
between reliability and temperature, but it's not linear. Then use the
temperature rise per W rating of the device to get to the surface
temperature.

In work I did >10 years ago all devices were directly bolted to the
liquid-cooled plate without an intermediate spreader, however, these LDMOS
devices are so small (ie very high heat density) there is a good reason to
spread the heat out first before cooling proper takes place, I'm somewhat
hazy what thickness, but you must achieve good flatness of contact against
the plate. Some very large devices eg IGBTs and rectifiers the size of your
open hand are supplied curved and the bolting-down process achieves the
flatness with the correct torque setting on the bolts.
Then you do the same sums as you do with air cooling ie temperature rise v
watts dissipated from the heat sink data.

Say you want to dissipate 1kW of heat continuously (eg in a data contest)
then a small 2 pass model would give you around 90 to 100K rise at the
surface of the plate with 1 US gallon per minute, whereas a 4 pass model
would give you around 20K rise on a 152mm length plate. This of course
assumes that the heat is being delivered into the plate evenly over the
whole surface, ie using a spreader. Heat sink paste adds a little to the
thermal gradient and is needed in very small amounts, evenly spread.

Do the sums several times with different criteria until you get to the one
you feel comfortable with. If you live in a cold climate you can dump the
heat into a small central heating radiator to keep the shack warm and no
fans required just an aquarian pump to run it; if you live in a hot place,
then put the radiator on the shade side of the house or even bury it. If
water is abundant, eg river water or a pond, you can re-cycle it back to the
source.

You can make your own water cooling plate, see here a small example cooling
a dozen TO-220 devices:
https://www.youtube.com/watch?v=WGpau-raMho
Somebody here will check my sums I'm sure.
73
David
G3UNA

----- Original Message -----
From: "Richard Solomon" <[hidden email]>
To: <[hidden email]>
Sent: Tuesday, December 16, 2014 4:44 PM
Subject: Re: [Elecraft] LDMOS for QRO [OT]

> If one wanted to use one of these to cool an LDMOS VHF KW, where would
> one find the design info to calculate which cold plate would provide
> sufficient
> cooling ?
>
> I envision a stack something like this:
>
> LDMOS PC Board
> Copper Heatsink (thickness need be determined)
> Cold Plate
> Aluminum Heat Sink (is this really necessary ?).
>
> 73 es HH, Dick, W1KSZ
>
>
> On 12/14/2014 4:32 PM, David Cutter wrote:
>> I'm a little surprised that folks in this group haven't suggested liquid
>> cooling for this modest application. Semiconductor cold plates have been
>> around for a long time, are economical to use and in my view a much
>> better solution than forced air cooling. They are compact, quiet, require
>> far less cabinet space, keep junctions cooler and more stable than air
>> could ever and enable higher reliability.
>>
>> Look at Aavid for instance, whose devices I used on many occasions:
>> http://www.aavid.com/sites/default/files/products/liquid/pdf/liquid-cold-plate-datasheet-hicontact.pdf
>>
>> If you play your cards right, you can cool the amplifier and the power
>> supply on a short 4-pass plate. Put the heat somewhere convenient, not in
>> your shack.
>>
>> 73
>>
>> David
>> G3UNA
>>

Elecraft mailing list

Re: LDMOS for QRO [OT]

This is really a fascinating idea. I have noticed that there are water
cooling kits made for computer CPU's. Some of the bigger CPU's run over
225 watts of power. I wonder how applicable one those CPU kits might
be. They include a heat sink, pump and radiator.
73, Doug -- K0DXV

On 12/16/2014 11:10 AM, David Cutter wrote:

> Hi Dick
>
> Start from the LDMOS data sheet and work out the temperature you wish
> to keep within at the junction. Because water cooling is so good, you
> can choose either to run the device cooler than you would with air
> cooling to improve reliability, or stick to the same temperature and
> get more power / use a smaller cooling plate / use less water. There's
> a direct relationship between reliability and temperature, but it's
> not linear. Then use the temperature rise per W rating of the device
> to get to the surface temperature.
>
> In work I did >10 years ago all devices were directly bolted to the
> liquid-cooled plate without an intermediate spreader, however, these
> LDMOS devices are so small (ie very high heat density) there is a good
> reason to spread the heat out first before cooling proper takes place,
> I'm somewhat hazy what thickness, but you must achieve good flatness
> of contact against the plate. Some very large devices eg IGBTs and
> rectifiers the size of your open hand are supplied curved and the
> bolting-down process achieves the flatness with the correct torque
> setting on the bolts.
> Then you do the same sums as you do with air cooling ie temperature
> rise v watts dissipated from the heat sink data.
>
> Say you want to dissipate 1kW of heat continuously (eg in a data
> contest) then a small 2 pass model would give you around 90 to 100K
> rise at the surface of the plate with 1 US gallon per minute, whereas
> a 4 pass model would give you around 20K rise on a 152mm length plate.
> This of course assumes that the heat is being delivered into the plate
> evenly over the whole surface, ie using a spreader. Heat sink paste
> adds a little to the thermal gradient and is needed in very small
> amounts, evenly spread.
>
> Do the sums several times with different criteria until you get to the
> one you feel comfortable with. If you live in a cold climate you can
> dump the heat into a small central heating radiator to keep the shack
> warm and no fans required just an aquarian pump to run it; if you live
> in a hot place, then put the radiator on the shade side of the house
> or even bury it. If water is abundant, eg river water or a pond, you
> can re-cycle it back to the source.
>
> You can make your own water cooling plate, see here a small example
> cooling a dozen TO-220 devices:
> https://www.youtube.com/watch?v=WGpau-raMho
> Somebody here will check my sums I'm sure.
> 73
> David
> G3UNA
>
> ----- Original Message ----- From: "Richard Solomon"
> <[hidden email]>
> To: <[hidden email]>
> Sent: Tuesday, December 16, 2014 4:44 PM
> Subject: Re: [Elecraft] LDMOS for QRO [OT]
>
>
>> If one wanted to use one of these to cool an LDMOS VHF KW, where would
>> one find the design info to calculate which cold plate would provide
>> sufficient
>> cooling ?
>>
>> I envision a stack something like this:
>>
>> LDMOS PC Board
>> Copper Heatsink (thickness need be determined)
>> Cold Plate
>> Aluminum Heat Sink (is this really necessary ?).
>>
>> 73 es HH, Dick, W1KSZ
>>
>>
>> On 12/14/2014 4:32 PM, David Cutter wrote:
>>> I'm a little surprised that folks in this group haven't suggested
>>> liquid cooling for this modest application. Semiconductor cold
>>> plates have been around for a long time, are economical to use and
>>> in my view a much better solution than forced air cooling. They are
>>> compact, quiet, require far less cabinet space, keep junctions
>>> cooler and more stable than air could ever and enable higher
>>> reliability.
>>>
>>> Look at Aavid for instance, whose devices I used on many occasions:
>>> http://www.aavid.com/sites/default/files/products/liquid/pdf/liquid-cold-plate-datasheet-hicontact.pdf
>>>
>>>
>>> If you play your cards right, you can cool the amplifier and the
>>> power supply on a short 4-pass plate. Put the heat somewhere
>>> convenient, not in your shack.
>>>
>>> 73
>>>
>>> David
>>> G3UNA
>>>
>
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:[hidden email]
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
> Message delivered to [hidden email]
>