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Author Topic: Who likes a pair of MRF157?  (Read 17004 times)
VK4DD
Member

Posts: 79




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« on: December 24, 2011, 11:40:59 PM »

Hi

Who likes a pair of MRF157? Nothing wrong with that?
I think Granberg wrote an application note for that.

http://www.macomtech.com/datasheets/MRF157.pdf

So my friend send me a reply and says yes Ron your not wrong.
So how about this one?

http://www.dnjradio.com//product_info.php?products_id=43&osCsid=7660d2e9c2cfed8ea3667b5039ff5e37

Any comments.

73 Ron
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ZENKI
Member

Posts: 980




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« Reply #1 on: December 25, 2011, 12:34:03 AM »

You have high expectations from an illegal CB linear amplifier factory!

Stuffing devices into a box and then calling it a  amplifier any idiot can do that, look at the rubbish  that the cbérs use.
We have enough application note amplifiers that have been copied for the last 30 years and none can really deliver the full IMD
potential of these devices across all bands.

Engineering the devices to deliver guaranteed performance across all the HF/vhf range is a serious design challenge.
Take all the current MRF150 amplifiers on the market, then measure their performance across all the bands and tell me why there is so much variation in IMD performance across the range. Trying to  squeezing -40db 3rd order out of any MRF150  amplifier across the ham bands and you will have yourself a real challenge.  I

Unfortunately their are few engineers out their in the ham industry who can really a design a decent solid state PA without using google or some application note. Expecting a Cb amp manufacturer to deliver a decent amplifier is asking a lot especially when they cant even manage something as simple as getting their amplifiers type accepted. I would not be a silly fool and invent such a large sum of money with an illegal CB amplifier manufacturer.

The devices are interesting non the less, having all you eggs in two baskets you would want to have a lot of faith in the protection circuits!



Hi

Who likes a pair of MRF157? Nothing wrong with that?
I think Granberg wrote an application note for that.

http://www.macomtech.com/datasheets/MRF157.pdf

So my friend send me a reply and says yes Ron your not wrong.
So how about this one?

http://www.dnjradio.com//product_info.php?products_id=43&osCsid=7660d2e9c2cfed8ea3667b5039ff5e37

Any comments.

73 Ron
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VK4DD
Member

Posts: 79




Ignore
« Reply #2 on: December 25, 2011, 01:24:22 AM »

You have high expectations from an illegal CB linear amplifier factory!

On what do you base this?

Stuffing devices into a box and then calling it a  amplifier any idiot can do that, look at the rubbish  that the cbérs use.
We have enough application note amplifiers that have been copied for the last 30 years and none can really deliver the full IMD
potential of these devices across all bands.

Do you have any facts on this amplifier? Or do you assume this.

Engineering the devices to deliver guaranteed performance across all the HF/vhf range is a serious design challenge.
Take all the current MRF150 amplifiers on the market, then measure their performance across all the bands and tell me why there is so much variation in IMD performance across the range. Trying to  squeezing -40db 3rd order out of any MRF150  amplifier across the ham bands and you will have yourself a real challenge.  I

Unfortunately their are few engineers out their in the ham industry who can really a design a decent solid state PA without using google or some application note. Expecting a Cb amp manufacturer to deliver a decent amplifier is asking a lot especially when they cant even manage something as simple as getting their amplifiers type accepted. I would not be a silly fool and invent such a large sum of money with an illegal CB amplifier manufacturer.

Its a Granberg application note, the IM3 guru from Motorola.

The devices are interesting non the less, having all you eggs in two baskets you would want to have a lot of faith in the protection circuits!

Yes big fets, but also big enough to cool in a decent way.
If you have one big tube you hall only one egg.
If the protection works than it works.

May be RM is getting serious because they read this forum and they decided to listen to you Zenki.

73 Ron.
« Last Edit: December 25, 2011, 02:49:32 AM by VK4DD » Logged
W5JON
Member

Posts: 174




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« Reply #3 on: December 25, 2011, 12:20:40 PM »

Zenki,

What is your amateur radio callsign, and why do you choose to make anonymous, unsubstantiated allegations on so many topics?

73,

John W5JON
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TANAKASAN
Member

Posts: 933




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« Reply #4 on: December 25, 2011, 12:55:20 PM »

For a working project using a pair of these devices see http://www.ibelings.com/n4ip/mrf157.html

Note the size of the heatsink and the heat spreader because a KW amplifier is a serious piece of kit. FYI the current price of the MRF157 from Mouser is 610 Dollars per device.

Tanakasan
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M0HCN
Member

Posts: 473




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« Reply #5 on: December 25, 2011, 03:25:18 PM »

Expensive parts, probably better to use 4 SD2933 with a magic T splitter/combiner, the sand works out much cheaper and it gives you a sane degraded mode of operation when it all goes wrong.

The SD2933 is ~$150, and good  for 300W balls out, so a pair on a amplifier module will give you 500W to the combiner for $300 on transistors, or ~1KW post combiner for $600 on transistors. Back it off to 800W or so and reliability (and IMD performance) will come up, and you could run to 4 sets for the cost of a single pair of 157's (~2KW all up, or 1KW of really clean, reliable power). 

Of course with that kind of thing the ferrite starts to cost, as does power and cooling, so the choice of sand may not be that huge a factor in overall amplifier cost, but I still say that 8 * SD2933 makes a better KW then 2 MRF157 for about the same money.

That RM amp has some 'interesting' features (VOX switching?), and the (granted, preliminary) data sheet is more then a little  thin on the details (IMD, Duty cycle, harmonics), but VOX is odd as it never works well on SSB, and I always figured it for a total CBism.

Merry Christmas all, Regards, Dan (Who has been drinking so if I have dropped one, that is why).
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ZENKI
Member

Posts: 980




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« Reply #6 on: December 25, 2011, 04:24:31 PM »

Unsubstantiated facts?

The biggest company selling illegal CB amplifiers fact?
No IMD performance data published fact?
No FCC type acceptance fact?

You seem to have a lot of faith in a company that has such a poor image problem in the ham market. You just willing too accept without
question the claims that this company makes blindly?

These are are the facts as they stand today.   If you have other data or information maybe you can present this data.

Zenki,

What is your amateur radio callsign, and why do you choose to make anonymous, unsubstantiated allegations on so many topics?

73,

John W5JON
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K1ZJH
Member

Posts: 1135




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« Reply #7 on: December 25, 2011, 04:27:32 PM »

Zenki

It seems many of FCC type accepted ham amplifiers also fail to meet your criteria.
Perhaps some of the RMI junk might be as good as the certified equipment, if they
are run within the limits for the active RF devices and  no to the exhorbitant adverstising
claims?

Pete
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W5JON
Member

Posts: 174




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« Reply #8 on: December 25, 2011, 05:32:00 PM »

Zenki,

Seems you did not answer the "what is your amateur radio callsign".  OVER

73,

John W5JON
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AD6KA
Member

Posts: 2238




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« Reply #9 on: December 25, 2011, 10:36:35 PM »

Quote
Perhaps some of the RMI junk might be as good as the certified equipment, if they are run within the limits for the active RF devices and  no to the exhorbitant (spadverstising (sp)
claims?
Seriously, if you think just running those "amps"
at lower power is going to clean up IMD your mistaken.
Low pass filters will help with harmonics but that is the easy problem.
LPF networks don't clean up IMD at all. Period, impossible.
They are NOT linear, are not designed to be linear,
(ineffective or none at all bias control circuitry)

There's good money to continue making and marketing
garbage CB amps with garbage PA transistors.

There's little money and a BIG RISK to redesign
a chunk of your product line with sophisticated
circuitry and established PA devices.
JUST FOR THE USA, cause nobody
in Europe has any qualms about putting that shit on the air.

Then....THEN you've got to advertise and compete against
long established products AND overcome your stigma of
"The CB Junk Amp Company".
Ken AD6KA
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K1ZJH
Member

Posts: 1135




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« Reply #10 on: December 26, 2011, 07:36:57 AM »

Some of the RMI amps do use 28 volt devices and avoid the common 12 volt CB power devices...

Tom Rauch has tested at least one of those amps, and posted the results on his webpage. Concluding
remarks:

 



90 watts PEP: The HLA-150 is a 90-watt PEP amplifier at best, and if operated that way will be acceptable for many uses. It is not as good as it could be for the very wide bandwidth distortion at higher power, but it is comparable to worse-case IMD for a common radio like the FT1000MP when it is at 90-watts PEP output.


The HL150 amplifier has exceptionally good harmonic suppression on most bands. The low-pass filters work well. It is an acceptable amplifier when operated at 90 watts PEP output or less.

 


It appears that running these amps conservatively might indeed improve IMD.  It is pretty sad to see the IMD can even be
compared to the typical IMD of what is a very popular transceiver.

Personally, if someone gave me one I'd consider using it after a 10 watt K2 or K3 on CW providing the harmonic suppression
meet FCC spec.

Pete
« Last Edit: December 26, 2011, 08:09:22 AM by K1ZJH » Logged
N3OX
Member

Posts: 8847


WWW

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« Reply #11 on: December 26, 2011, 08:31:56 AM »

It appears that running these amps conservatively might indeed improve IMD.  It is pretty sad to see the IMD can even be
compared to the typical IMD of what is a very popular transceiver.

I want to know TWO things about the above comments.

1) Does the FT-1000MP on the worst band have excessive 9th, 11th, 13th, etc. products like the HLA-150V? or is it just the third-order spec that is comparable? The higher order products are not such a big deal for a 100W-ish amplifier used by a typical backyard ham station on 75m or 20m, but if you are on a quiet band or have particularly good antennas and propagation coming together, distortion products that don't roll off strongly are kind of evil.  Maybe some popular ham rigs that are likely to get coupled to decent antennas are kind of evil too Sad

It's kind of like the Flexradio spur problem a while back, where there was an exact copy of the CW signal down 2.4kHz or something that was a LEGAL amount of spurious emission, but on 160m that spur was routinely S7 or S8 because the main signal it was associated with with was S9+30dB.

2) How can we expect people to operate their RM Italy amplifier conservatively at 90W when the webpage says that a HLA-150V will put out 250W PEP on SSB?

http://www.rmitaly.com/scheda.asp?IDGr=1&cat=19&tipo=186

That spec is meaningless for an amplifier that saturates at 155W. 

The mistrust I have because of that is enough for me to firmly say that I won't give RM Italy four thousand bucks for a BLA-1000 even if independent testing shows it to be just fine.  If RM Italy starts giving honest technically reasonable specs on all of their amplifiers, drops their entire unfiltered CB amp product line, and so forth I might buy something from them.  But I very much doubt that it's hams buying $4000 "kW" amps that are their bread and butter.  I have a suspicion that it's really hundreds of thousands of active CB/freeband types buying the little red ones that don't even have harmonic filtering.

For what it's worth I bet the good harmonic filtering on the HLA-150V is a marketing trick aimed at assuaging hams who have been told that RM Italy amps don't even have harmonic filtering. The last time I looked at a "KL" series when a ham asked about one, there was nothing in the schematic past the transistors besides a broadband ferrite transformer and a T/R relay.

Technical issues aside, I personally don't want to support such a manufacturer. 
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73,
Dan
http://www.n3ox.net

Monkey/silicon cyborg, beeping at rocks since 1995.
K1ZJH
Member

Posts: 1135




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« Reply #12 on: December 26, 2011, 09:25:53 AM »

Oh, I'd never buy one.... but, if someone gifted one I'd be tempted to put it on the bench and
see what can  be done with it.  At a minimum, and with harmonic filtering, it might have some
use for perking up a QRP CW rig. 

The higher order IMD products that go on forever would bother me. But, I have to wonder what
sort of IMD specs my 100 watt solid state amps have on 6 and 2 meters, and on 432MHz.
They are all American made.
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VK4DD
Member

Posts: 79




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« Reply #13 on: December 26, 2011, 06:45:37 PM »

Oh, I'd never buy one.... but, if someone gifted one I'd be tempted to put it on the bench and
see what can  be done with it.  At a minimum, and with harmonic filtering, it might have some
use for perking up a QRP CW rig. 

The higher order IMD products that go on forever would bother me. But, I have to wonder what
sort of IMD specs my 100 watt solid state amps have on 6 and 2 meters, and on 432MHz.
They are all American made.

Do you  mean that the MRF157 is not a clean fet?
Have you got IMD measurements or other data to substantiate this claim?

73 Ron.
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K1ZJH
Member

Posts: 1135




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« Reply #14 on: December 26, 2011, 07:51:00 PM »

Oh, I'd never buy one.... but, if someone gifted one I'd be tempted to put it on the bench and
see what can  be done with it.  At a minimum, and with harmonic filtering, it might have some
use for perking up a QRP CW rig. 

The higher order IMD products that go on forever would bother me. But, I have to wonder what
sort of IMD specs my 100 watt solid state amps have on 6 and 2 meters, and on 432MHz.
They are all American made.

Do you  mean that the MRF157 is not a clean fet?
Have you got IMD measurements or other data to substantiate this claim?

73 Ron.


Ron

Which RMI amplifiers use the MRF157?  I never said anything about the MRF157 in any of
my posts.

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