Call Search
     

New to Ham Radio?
My Profile

Community
Articles
Forums
News
Reviews
Friends Remembered
Strays
Survey Question

Operating
Contesting
DX Cluster Spots
Propagation

Resources
Calendar
Classifieds
Ham Exams
Ham Links
List Archives
News Articles
Product Reviews
QSL Managers

Site Info
eHam Help (FAQ)
Support the site
The eHam Team
Advertising Info
Vision Statement
About eHam.net

   Home   Help Search  
Pages: [1]   Go Down
  Print  
Author Topic: Cheap eBay Amps - are they any good?  (Read 4500 times)
G7DMQ
Member

Posts: 40




Ignore
« on: March 24, 2013, 10:59:24 AM »

Things like this:
http://www.ebay.co.uk/itm/RM-KL-400-CB-HF-AMPLIFIER-burner-/160963272475?pt=UK_Mobile_Phones_Communication_Ham_Radio_Amplifiers&hash=item257a289f1b

It claims to work between 3 & 30Mhz - and I just wondered what the difference in use is between something like this and one costing several times more?

I have been considering building, effectively an SDR using a microcontroller (something like a Raspberry Pi) which is unlikely to spit out more than a couple of watts.  I wondered if something like this would be a reasonable way to get a decent amount of power out of it - without breaking the bank!

Si
Logged
N4ATS
Member

Posts: 849




Ignore
« Reply #1 on: March 24, 2013, 11:59:48 AM »

They work very well , however not US Type Accepted which is a shame as those overseas companies have plenty to offer but good 'ole USA won't honor because of.

I have a 300 watt RM HF Amp , it has been working flawless for 8 years.

Logged
W6GX
Member

Posts: 3003




Ignore
« Reply #2 on: March 24, 2013, 12:02:11 PM »

Does it have any protection circuitry to protect the output transistors?  Why would the FCC not approve them if they meet the specs?

73,
Jonathan W6GX
Logged
W8JX
Member

Posts: 6472




Ignore
« Reply #3 on: March 24, 2013, 12:57:31 PM »

Does it have any protection circuitry to protect the output transistors?  Why would the FCC not approve them if they meet the specs?

73,
Jonathan W6GX

Maybe because they support CB right out of the box. If so, that's a no go here with FCC.
Logged

--------------------------------------
All posted wireless using Win 8.1 RT, a Android tablet using 4G/LTE/WiFi or Sprint Note 3.
K2OWK
Member

Posts: 1073




Ignore
« Reply #4 on: March 24, 2013, 01:36:47 PM »

I have a question related to these RM amps. I realize they are not FCC type accepted, but from my understanding this means it is against FCC rules to sell them in the US (the amps being of commercial manufacture and capable of operating on 11 meters). As a licensed ham radio operator, it is my understanding that I can operate any type of transmitters in the ham band provided they are operated in good radio practice. I am responsible for my transmissions. I can operate home built equipment. I can not understand why I could not use these RM transmitters, if they meet FCC emission standards? I know the company is not supposed to sell non type excepted equipment, but it is not illegal to buy it, or operate it as licensed a ham, why all the problems? If I legally bought a home brew linear from a fellow ham, this would not be type accepted, but I could still use it legally. The heathkit SB-200 series liners are not type accepted and will operate 11 meters as built (11 meters was a ham band back in my day). This all confuses me. Can I operate this RM amplifier, or for that matter any commercial linear amplifier that is not FCC type accepted as long as it meets emission standards for good operation procedure?

73s

K2OWK  
Logged
G3RZP
Member

Posts: 4845




Ignore
« Reply #5 on: March 24, 2013, 03:05:01 PM »

It depends whether or not you are talking USA or EU. In the EU (27 countries) equipment 'placed on the market' i.e. generally offered for sale must meet the requirements of various Directives - basically the EMC Directive and the Radio & Telecommunications Terminal Equipment Directive. (R&TTED).  Pre-used, home brew and kits all intended for use by radio amateurs are exempt. (What about model train controller kits and the like that produce wicked radio noise? Being basically a load of technically incompetent idiots in the European Commission, they never thought of that! - so they get through as 'kits'.)

What is NOT stated about the RM amplifiers is what EU Harmonised Standards they meet, or, if not, what Competent Body reports apply to show compliance.

In the EU, a company with an adequate (e.g. ISO9000 compliance certificate) can 'self certify'. They have to have adequate paperwork...............but they can self certify. Since compliance monitoring other than in Germany basically doesn't exist  (and even in Germany it's a bit sketchy), a manufacturer can get away with murder. If the whole situation goes t*ts up, he can go into liquidation and start again.....

And the idiots in Brussels cannot get their heads around this state of affairs.......

Sorry guys, I do this for a living......
Logged
G7DMQ
Member

Posts: 40




Ignore
« Reply #6 on: March 24, 2013, 04:48:38 PM »

So, should I buy one?  To go with my non FCC or EU approved, yet to be built transceiver?

Si
Logged
W4OP
Member

Posts: 441


WWW

Ignore
« Reply #7 on: March 24, 2013, 04:51:54 PM »

From what I can see, the amplifier in question does not have a bandswitch- thus it has no output filtering (except maybe for 10/11M). So in addition to the amp,  be prepared to buy build a filter set and a way to switch them when you change bands.

Dale W4OP
Logged
W9GB
Member

Posts: 2656




Ignore
« Reply #8 on: March 24, 2013, 04:55:11 PM »

eBay sellers that use "Private listing / registration" is a NO BUY, in my book.

RM ITALY HLA-150 tests
http://www.w8ji.com/rm_hla-150_test.htm

The DX Shop Limited (UK) acquired the business of Linear Amp UK in the Autumn of 2012 from Paul Cullen.  No interest in these products?
http://linamp.co.uk/
« Last Edit: March 24, 2013, 04:57:46 PM by W9GB » Logged
AD6KA
Member

Posts: 2238




Ignore
« Reply #9 on: March 24, 2013, 11:16:10 PM »

Quote

The HLA-150, though till a questionable amp,
(will only hold specs to 90 watts, no further)
is a far different animal than the one in the link
the poster provided.
THAT one is only for CB.
Like the man said, it'll probably just work on
10 & 11m anyway.

As for just adding low pass filters to those kind
of amps, they will do nothing for IMD, the real problem.

Stay away, stay very far away.

If you absolutely can't afford a Type Accepted amp(or whatever
the current term is.) At least look at the decks built
by 4z4rb,Baruch on ebay. At least he adds good bias
and fold back protection circuits. You'lll have to add LPF's
an enclosure, fan, etc. An example:
http://www.ebay.com/itm/SDR-QRP-45W-driver-LINEAR-AMPLIFIER-MODULE-PRE-DRIVER-/150993410099#vi-content
I am sure Zenki will jump in here with both feet soon....
73, KEN  ad6KA
Logged
K1ZJH
Member

Posts: 1150




Ignore
« Reply #10 on: March 25, 2013, 07:15:36 AM »

Even though RMI claims that amp will do 400 watts on SSB, the claim is utter nonsense! It is rated for two hundred watts on CW, and that will be the same for SSB peak power.  And that's providing the amplifier isn't being driven into flat-topping, with horrendous distortion products.
Logged
G7DMQ
Member

Posts: 40




Ignore
« Reply #11 on: March 25, 2013, 08:19:21 AM »

I'll take that as a 'NO' then!

Are there any 'good value' (read cheap) amps which will do a decent job on 40 & 60m (there's too much noise on 80 round here)?

Slightly off topic, has anyone made a 'digital' amp for HF?  By digital, I mean pulse width modulation with filtering on the output to smooth it out.

I've built a couple of motor speed controllers, using IGBT's delivering up to 60kw into a motor.  Typical THD of less than 1% (what sort of THD figure do you need for radio?).  Granted, these were only clocking at 80kHz - and upping that by 100x would be a problem efficiency wise because of the relatively high gate capacitance giving rise to slow on/off transitions, but maybe not impossible?  It may be that the efficiency suffers to the point that a class B is more efficient?

Si
Logged
M0HCN
Member

Posts: 473




Ignore
« Reply #12 on: March 25, 2013, 12:27:34 PM »

The thing about an RF amp is that by and large we do NOT care about the shape of the RF (That is what lowpass filters are for!), but we care deeply about the shape of the envelope.

There are good ways to make an efficient 'digital' amp for HF, but they typically do not do direct PWM and usually require additional signals from the exciter, further they are often rather narrowband (See the class E stuff beloved of the AM Phone crowd). HF extends across ~4 octaves, which is way too wide for easy direct PWM or such (Harris have a PWM rig for shortwave broadcast but it is not exactly frequency agile).

One efficiency trick that occurred to me is to note that most amps are specified to deliver full power into 1.5:1, meaning that the drain match has to be such that full power will be delivered into 75 ohms, now that means that for the same power into 50 ohms the transistors are dissipating quite a lot of heat because the AC component of the drain voltage is smaller then optimal. However if one placed an impedance bridge at the output of the PA then feed |V|/|I| back to a switchmode power supply, the drain voltage could be set to only that required for the load impedance actually being presented (Especially helpful when running a rig that can do full power into 1.5:1 hi Z at 1.5:1 low Z....).
Result: less heat and efficiency much closer to that typical of a tube amp with its variable match (at least for resistive loads).
I have been getting some promising results from feeding the envelope to a buck converter so as to have the supply partially track the envelope, but that really needs advanced feedback techniques to compensate the resulting phase modulation, at which point you have a transmitter as opposed to an amplifier. 

73 M0HCN.
Logged
G3RZP
Member

Posts: 4845




Ignore
« Reply #13 on: March 25, 2013, 01:33:57 PM »

In the European Union, the legal position is that any equipment 'placed on the market' i.e. offered for sale as a commercial venture should carry a CE mark. Where the vendor, or the manufacturer if not the vendor, has an adequate QA system (e.g. ISO 9000 approval), he/she  may self certify that the equipment meets a Harmonised European Standard (HEN): in the case of commercially available amateur radio equipment, this means EN 301 783 -2 and EN301 489-1 and EN301 489 -15. If they do not have a approved QA system, they should have a technical file and a certification from a Notified Body that the equipment meets the requirements of the applicable Directives.

In the UK, failure to do this can carry a fine of up to £5000 or a 6 month prison sentence. If the equipment is not commercially available e.g. you've made one but that's it or it's a kit or it is pre-used, the requirements don't apply.

Enforcement is almost non existent......except maybe in Germany. It's case of 'no problems, no worries to the Administrations'.

Realistically, they could have totally exempted all amateur radio equipment. The problems caused by commercial gear is usually lack of immunity in the victim, so all they do is add expense.


But the Brussels bureaucrats know almost nothing about the technicalities, and generally, they are incompetent lawyers as well.....

OK, I am a cynic. I also deal with this rubbish professionally......
Logged
Pages: [1]   Go Up
  Print  
 
Jump to:  

Powered by MySQL Powered by PHP Powered by SMF 1.1.11 | SMF © 2006-2009, Simple Machines LLC Valid XHTML 1.0! Valid CSS!