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Author Topic: Who likes a pair of MRF157?  (Read 15404 times)
N3OX
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Posts: 8854


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« Reply #15 on: December 26, 2011, 08:11:14 PM »

Quote from: K1ZJH
Which RMI amplifiers use the MRF157?

The RMI BLA-1000 in VK4DD's original post uses them.  It seems to show quite good IMD in a 2 tone test at 500W output according to IK4AUY's webpage.  I don't know about 1kW.
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73,
Dan
http://www.n3ox.net

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

Posts: 911




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« Reply #16 on: December 26, 2011, 08:28:24 PM »

The MACOM data sheet has IMD specifications of -25db at 30mhz.

This is the point I was originally trying to make. Just stuffing 2 devices in box  and making claims that the amp is clean should be tempered  with caution until this fact can be proven.  Here we have the manufacturer of the device stating that the IMD is marginal  and yet we have the  manufacturer and its supporters making unsubstantiated claims that the amp is clean.

If RM or anyone else wants to make claims that the amp is clean they should provide evidence that proves that it is clean. Its not hard doing these measurements, but I would bet that RM Italy would not even own a spectrum analyzer and test jig to make IMD measurements. Since i dont see that data published anywhere i can just assume that the claims are  marketing hype.

Its an engineering challenge to design a amplifier with decent IMD performance that holds across the entire HF range. Data sheet circuits with one set of IMD measurements at one frequency does not prove that the amplifier can maintain its performance across the HF range.

There is an excellent published treatise on this subject: High Linearity RF Amplifier Design by Peter B Kenington This book covers  this challenge in great detail. Maybe some people should do more research rather  than believing marketing hyperbola by the manufacturer.




Quote from: K1ZJH
Which RMI amplifiers use the MRF157?

The RMI BLA-1000 in VK4DD's original post uses them.  It seems to show quite good IMD in a 2 tone test at 500W output according to IK4AUY's webpage.  I don't know about 1kW.
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VK4DD
Member

Posts: 79




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« Reply #17 on: December 26, 2011, 08:55:51 PM »

Hi

This post was not about the RM 1000MB amplifiers or other CB gear but only about these MRF157. So I was a little confused when the discussion all of a sudden went in that direction.

I liked these MRF157 because they have a big flat cooling area with 4 screws to bolt them down to a heat sink. This making them much easier to cool in comparison with other fets.
The down side it that I am not impressed by IM3 so far. -29dB IM3 which is basicly 23dB above the IM3 products which I think is marginal for these expensive bits. I would have expected better from $900 for a pair of fets.

On the other end these things might last for ever when properly cooled.

BTW if you do a search in this forum than you will find the RM 1000MB amplifier as a stand alone topic, off course Zenki gave it his usual recommendations.

73 Ron.


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W5JON
Member

Posts: 163




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« Reply #18 on: December 27, 2011, 06:40:20 AM »

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: 949




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« Reply #19 on: December 27, 2011, 09:13:01 AM »

Hi

This post was not about the RM 1000MB amplifiers or other CB gear but only about these MRF157. So I was a little confused when the discussion all of a sudden went in that direction.
 73 Ron.




Hi Ron

I didn't make the connection between the DNJ reference and the RMI until I reread the first post and clicked on the
hyperlinks... 

Pete
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VK4DD
Member

Posts: 79




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« Reply #20 on: December 27, 2011, 11:51:44 AM »

Hi Pete,

Don't worry these these happen all the time to me as well.

Ron.
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VK4DD
Member

Posts: 79




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« Reply #21 on: December 27, 2011, 12:17:37 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

Hi John,

I counted 3 of your post, and Zenki would have seen them for sure.

Personally I read his posts but don't take them to seriously. I laugh about them but VK4AKV got really offended by his post over his 12V amplifier (when I wrote about his doorknob band filter). Zenki accused it of being a splatter amp while VK4AKV build it using Granberg application notes for low IM3.  But I do agree that if you write in these HAM radio forums you should use your call sign. I mean who is Zenki, he might as well be a ghost Roll Eyes.

On the other hand he seems to know a lot and stirs up some good discussion too.

Don't take it too serious, this is just a hobby.

73 Ron.

« Last Edit: December 27, 2011, 12:21:32 PM by VK4DD » Logged
ZENKI
Member

Posts: 911




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« Reply #22 on: December 27, 2011, 04:55:29 PM »

DNJ Radio another illegal seller of CB amplifiers most of which end up on the US market.  I wonder when the FCC will close them down? OH I forgot its for export only!


Hi

This post was not about the RM 1000MB amplifiers or other CB gear but only about these MRF157. So I was a little confused when the discussion all of a sudden went in that direction.
 73 Ron.




Hi Ron

I didn't make the connection between the DNJ reference and the RMI until I reread the first post and clicked on the
hyperlinks... 

Pete
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ZENKI
Member

Posts: 911




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« Reply #23 on: December 27, 2011, 05:24:23 PM »

Well your friend can measure the IMD of his amplifier and post his results, put up or shutup as the saying goes. On second thought dont bother, every mother loves their baby even if it looks like it got beat up with the engineering ugly stick in terms of performance!

This is what infuriates me about new hams. They have this attitude because that they doing something today that other hams did 30 years ago, and also measured 30 years ago, it is of no relevance and importance to them what others did before them. They feel as if they are the ones inventing the light globe.

This  same stupid attitude persists with hams who use CB  amplifiers on the ham bands. They used them on the CB band for past 20 years so they know different and think that they are experts at driving class C amps in a clean manner. In reality they just idiots. If it was  possible to build a clean  2sc2879 amplifier and run it in cleaner manner  many hams would have done so a long time ago. You can put lipstick on a pig however its still a pig and this comment applies to all  2sc2879 amplifiers. Now there is no doubt that in a typical low efficient  mobile installation that they are practical and work, they are horrendous amplifiers to be using on a home station with a big antenna purely because their IMD performance is so poor.

I hear a ZL station on the longpath on 20 meters just  about every day. He runs his ham station from a CAR attached to a fixed antenna. His running a 12 volt mobile amplifier. In Europe when he is only S9  we can hear his splatter. There are numerous comments on the cluster  about his poor signal. I guess these kinds of people just dont get it.

If you friend was such a great  engineer, prudence would have told him to build a proper  FET amplifier and not get his wise inspirational ideas from the CBérs. Granberg was smart enough to know what good IMD performance was, he measured  the IMD performance of  amps  a million times over. Its a long bow to draw that just because he read and copied someone else's  application note that his baby is automatically the gold standard for IMD performance. Certainly if he read through Granbergs notes he would have come to the conclusion  in the first few applications notes that 12 volt devices are not the best choice if you seeking the best IMD performance. He probably thought that the CBérs are doing it, it must be OK? If he feels he has  managed to turn a filthy 2sc2879 into a IMD marvel I suppose he should submit his work for publishing in QEX.

Wise ham cleans up CB amp from 30 years ago, it should make good reading.



DNJ Radio another illegal seller of CB amplifiers most of which end up on the US market.  I wonder when the FCC will close them down? OH I forgot its for export only!


Hi

This post was not about the RM 1000MB amplifiers or other CB gear but only about these MRF157. So I was a little confused when the discussion all of a sudden went in that direction.
 73 Ron.




Hi Ron

I didn't make the connection between the DNJ reference and the RMI until I reread the first post and clicked on the
hyperlinks... 

Pete
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VK4DD
Member

Posts: 79




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« Reply #24 on: December 27, 2011, 11:12:04 PM »

Well your friend can measure the IMD of his amplifier and post his results, put up or shutup as the saying goes. On second thought dont bother, every mother loves their baby even if it looks like it got beat up with the engineering ugly stick in terms of performance!

This is what infuriates me about new hams. They have this attitude because that they doing something today that other hams did 30 years ago, and also measured 30 years ago, it is of no relevance and importance to them what others did before them. They feel as if they are the ones inventing the light globe.

This  same stupid attitude persists with hams who use CB  amplifiers on the ham bands. They used them on the CB band for past 20 years so they know different and think that they are experts at driving class C amps in a clean manner. In reality they just idiots. If it was  possible to build a clean  2sc2879 amplifier and run it in cleaner manner  many hams would have done so a long time ago. You can put lipstick on a pig however its still a pig and this comment applies to all  2sc2879 amplifiers. Now there is no doubt that in a typical low efficient  mobile installation that they are practical and work, they are horrendous amplifiers to be using on a home station with a big antenna purely because their IMD performance is so poor.

I hear a ZL station on the longpath on 20 meters just  about every day. He runs his ham station from a CAR attached to a fixed antenna. His running a 12 volt mobile amplifier. In Europe when he is only S9  we can hear his splatter. There are numerous comments on the cluster  about his poor signal. I guess these kinds of people just dont get it.

If you friend was such a great  engineer, prudence would have told him to build a proper  FET amplifier and not get his wise inspirational ideas from the CBérs. Granberg was smart enough to know what good IMD performance was, he measured  the IMD performance of  amps  a million times over. Its a long bow to draw that just because he read and copied someone else's  application note that his baby is automatically the gold standard for IMD performance. Certainly if he read through Granbergs notes he would have come to the conclusion  in the first few applications notes that 12 volt devices are not the best choice if you seeking the best IMD performance. He probably thought that the CBérs are doing it, it must be OK? If he feels he has  managed to turn a filthy 2sc2879 into a IMD marvel I suppose he should submit his work for publishing in QEX.

Wise ham cleans up CB amp from 30 years ago, it should make good reading.


I am terribly sorry its not my intention to upset you or any one else in this forum.
I will no longer talk about a certain Italian brand which used to produce CB stuff that was a mistake.

Any way Zenki you wanted to talk about IM3 and stirred up my harmonic doorknob filter post. I opened this IM3 topic especially for you. Now after 200 posts and almost 10.000 hits later I think I won't post any more in this topic. I pretty much got the picture after reading the first 20 posts. I would have been happy to buy you a beer when I see you in Friedrich haven or Dayton but pfff I dunno who to look for.

73 Ron.

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K1ZJH
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Posts: 949




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« Reply #25 on: December 28, 2011, 08:31:00 AM »

Don't take these forums too seriously Ron. When Zenki rants and raves about the 2SC2879 being
a crap CB transistor, it should be mentioned that it was used in Henry and Ameritron amplifiers,
and in numerous other ham equipment, that was legally sold in the USA.  Grin Grin

Pete
« Last Edit: December 28, 2011, 08:51:09 AM by K1ZJH » Logged
ZENKI
Member

Posts: 911




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« Reply #26 on: December 29, 2011, 01:24:19 AM »

That might be so. However that does not change the fact that the IMD performance of these 2SC2879's are poor. Why dont we stick with issue.  The issue was not if was legal or not or whether lots of companies use these devices. The issue was  do these devices  produce acceptable IMD performance? The answer is  to that is question is no.  If you can provide evidence to the contrary you can present that evidence. What is worst is that the device is no longer manufactured  by the original manufacturer so who knows what the ultimate performance is of all these copy devices. The originals were already bad enough especially on the higher frequencies.

We all want cheap affordable amplifiers tube or otherwise. I dont think having a cheap high power amplifier at the expensive of IMD performance is an acceptable way of doing things. Just go down to the CB band if you want a reminder of what power for the sake of power without regards to  good engineering practice means.

I just find it ironic how hams were supposed to have the technical high moral ground, and in many places we find our minds and engineering abilities are down in the gutter with the CBérs!

Don't take these forums too seriously Ron. When Zenki rants and raves about the 2SC2879 being
a crap CB transistor, it should be mentioned that it was used in Henry and Ameritron amplifiers,
and in numerous other ham equipment, that was legally sold in the USA.  Grin Grin

Pete
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VE7RF
Member

Posts: 212




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« Reply #27 on: December 29, 2011, 06:53:00 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.

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.

##  NO , it's NOT.  Just look at the link the fellow provided in the very 1st post. [data sheet].  IMD3 @ 30 mhz..and 600w pep out [ ONE device] is a paltry -25 db. Some Italian station recently measured the IMD on this 1 kw rm italy amp and it was pretty damn good...but that was backed down to 500w pep out.   The problem is, at 500w pep out, the eff is lousy,since the xfmr is not desgined for a higher load Z.   I read the manual for that kw rm amp..and it also meters eff.  And you can not run the amp at less than 400w!  The eff is so low at  that power level, that it kicks itself offline.

##  I also looked at all their other amps they make...typ listed as  "10/12M amps"  or  "10m amps" and all of those only need 5 watts to drive em, and some are as low as 1/2 watt.  Some are listed as "20-30 mhz" .  Any idiot can see these are designed for the 11m market...esp when they have em optimized for the 10/11/12m bands.

later... Jim  VE7RF     
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VE7RF
Member

Posts: 212




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« Reply #28 on: December 29, 2011, 06:57:00 AM »

Zenki,

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

73,

John W5JON

##  "zenki" doesn't post his callsign  for a specific reason. I know who he is.  Suffice to say, he's the real deal and no BS artist.  Besides, posting one's callsign violates the privacy act. Post your callsign, and every nutcase now has your street address too.

later... Jim  VE7RF
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VE7RF
Member

Posts: 212




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« Reply #29 on: December 29, 2011, 07:01:24 AM »

Don't take these forums too seriously Ron. When Zenki rants and raves about the 2SC2879 being
a crap CB transistor, it should be mentioned that it was used in Henry and Ameritron amplifiers,
and in numerous other ham equipment, that was legally sold in the USA.  Grin Grin

Pete

##  It was used in the Ameritron AL-500 mobile  500w amp.  It is junk. Even Ameritron specs it at -25db  IMD3.  W8JI was gonna suggest to Ameritron, that the AL-500 only be used in mobile applications...and NOT used at home..like with real ants. Stick a big 13.8 vdc supply on that thing..and then into the yagi..and you will not be popular.  In a Mobile, ur signal isn't loud enough to start with.

later... Jim   VE7RF
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