KPA500 Combiner - MFJ ACB-1000


j
 

Has anyone tried the MFJ ACB-1000 combiner with a pair of KPA500's?  TNX,  Jeff / K1ZN


Ken K6MR
 

I have not tried specifically the MFJ combiner (and don’t forget you’ll also need the splitter for the inputs) but I used the W6PQL splitter/combiner units for 4 years.  Worked fine.

 

Ken K6MR

 

From: j
Sent: Wednesday, April 28, 2021 15:43
To: Elecraft-K3@groups.io
Subject: [Elecraft-K3] KPA500 Combiner - MFJ ACB-1000

 

Has anyone tried the MFJ ACB-1000 combiner with a pair of KPA500's?  TNX,  Jeff / K1ZN

 


CW CW
 

Interesting piece of equipment.

N5CW

On Wednesday, April 28, 2021, 05:43:35 PM CDT, j <jacantor9@...> wrote:


Has anyone tried the MFJ ACB-1000 combiner with a pair of KPA500's?  TNX,  Jeff / K1ZN


Bob McGraw - K4TAX
 

It is interesting that no loss figure is given in the specs.   I've never known of a combiner design that didn't have some amount loss.  I guess this is typical of MFJ, attaining performance that flies in the face of laws of physics. 

73

Bob, K4TAX

On 4/28/2021 5:42 PM, j wrote:
Has anyone tried the MFJ ACB-1000 combiner with a pair of KPA500's?  TNX,  Jeff / K1ZN


David Bunte
 

Bob -

I don't understand your statement "I guess this is typical of MFJ, attaining performance that flies in the face of laws of physics."

I only glanced at the item in the MFJ Catalog but did not see any claim that is patently false. They say the device combines the output of two amplifiers... I did not see a claim that it accomplished that without loss. Did you see a claim that I missed, or are you just choosing to bash MFJ?

Dave - K9FN


On Sat, May 1, 2021 at 9:55 PM Bob McGraw - K4TAX <rmcgraw@...> wrote:

It is interesting that no loss figure is given in the specs.   I've never known of a combiner design that didn't have some amount loss.  I guess this is typical of MFJ, attaining performance that flies in the face of laws of physics. 

73

Bob, K4TAX

On 4/28/2021 5:42 PM, j wrote:
Has anyone tried the MFJ ACB-1000 combiner with a pair of KPA500's?  TNX,  Jeff / K1ZN


Mark Morin
 

On Sat, May 1, 2021 at 08:01 PM, David Bunte wrote:
Bob -
 
I don't understand your statement "I guess this is typical of MFJ, attaining performance that flies in the face of laws of physics."
 
I only glanced at the item in the MFJ Catalog but did not see any claim that is patently false. They say the device combines the output of two amplifiers... I did not see a claim that it accomplished that without loss. Did you see a claim that I missed, or are you just choosing to bash MFJ?
 
Dave - K9FN

Dave, as soon as I saw this product, the first question that popped into my mind was losses. Transmitter combiners always have loss and it’s usually quite significant. I downloaded the very scant “manual”, which does not include any loss specification but it does say that you can obtain twice the power compared to a single amplifier. That statement implies zero loss, which is physically impossible. 

So I’m with Bob on this on. It looks and smells like snake oil to me. 

Mark VA2MM 


David Bunte
 

Mark -

I see your point. Had I seen that I would at least have done an eyeball roll. 

My apologies to Bob. 

Dave - K9FN 

On Sun, May 2, 2021 at 7:49 AM Mark Morin <mark@...> wrote:
On Sat, May 1, 2021 at 08:01 PM, David Bunte wrote:
Bob -
 
I don't understand your statement "I guess this is typical of MFJ, attaining performance that flies in the face of laws of physics."
 
I only glanced at the item in the MFJ Catalog but did not see any claim that is patently false. They say the device combines the output of two amplifiers... I did not see a claim that it accomplished that without loss. Did you see a claim that I missed, or are you just choosing to bash MFJ?
 
Dave - K9FN

Dave, as soon as I saw this product, the first question that popped into my mind was losses. Transmitter combiners always have loss and it’s usually quite significant. I downloaded the very scant “manual”, which does not include any loss specification but it does say that you can obtain twice the power compared to a single amplifier. That statement implies zero loss, which is physically impossible. 

So I’m with Bob on this on. It looks and smells like snake oil to me. 

Mark VA2MM 


Bob McGraw - K4TAX
 

Combiners of and any form have loss.  Therefore using 2 amplifiers of equal power will not produce twice the power of one amplifier.  I'm not bashing MFJ, but I am disputing their written claims. 

If they specified using two identical amplifiers and the inputs were driven 180 degrees and then combined accordingly, this might make more sense as the combined power stage would be push-pull.  To be effective, the phase shift through the system would have to be maintained very carefully, including identical electrical lengths of input and output coax lines. 

I can visualize the use of conventional tube amps and there associated Tune and Loading circuits, not having identical phase relationships,  producing horrifying signal results on the bands.  

The system may work great, but buyer beware. 

73

Bob, K4TAX

On 5/2/2021 6:49 AM, Mark Morin wrote:
On Sat, May 1, 2021 at 08:01 PM, David Bunte wrote:
Bob -
 
I don't understand your statement "I guess this is typical of MFJ, attaining performance that flies in the face of laws of physics."
 
I only glanced at the item in the MFJ Catalog but did not see any claim that is patently false. They say the device combines the output of two amplifiers... I did not see a claim that it accomplished that without loss. Did you see a claim that I missed, or are you just choosing to bash MFJ?
 
Dave - K9FN

Dave, as soon as I saw this product, the first question that popped into my mind was losses. Transmitter combiners always have loss and it’s usually quite significant. I downloaded the very scant “manual”, which does not include any loss specification but it does say that you can obtain twice the power compared to a single amplifier. That statement implies zero loss, which is physically impossible. 

So I’m with Bob on this on. It looks and smells like snake oil to me. 

Mark VA2MM 


Virus-free. www.avg.com


Lou W7HV
 

Hah.  Yeah.  Dumping on MFJ is never out of style.  I always figured the more one knew and understood, the better use they'd get out of MFJ products. I have a few that have served me and met my appropriately set expectations for many years.  Coincidentally, I happened to notice MFJ has 14 full page ads in the May QST. That can be viewed in a number of ways, but MFJ is certainly helping pay for the publication of the mag.

Lou W7HV 


K9MA
 

Lack of active cooling suggests that the loss can't be large: a 1dB loss would be about 300 W.

The manual definitely should specify equal cable lengths.

73,
Scott K9MA 

----------

Scott Ellington

 --- via iPad

On May 2, 2021, at 7:53 AM, Bob McGraw - K4TAX <rmcgraw@...> wrote:



Combiners of and any form have loss.  Therefore using 2 amplifiers of equal power will not produce twice the power of one amplifier.  I'm not bashing MFJ, but I am disputing their written claims. 

If they specified using two identical amplifiers and the inputs were driven 180 degrees and then combined accordingly, this might make more sense as the combined power stage would be push-pull.  To be effective, the phase shift through the system would have to be maintained very carefully, including identical electrical lengths of input and output coax lines. 

I can visualize the use of conventional tube amps and there associated Tune and Loading circuits, not having identical phase relationships,  producing horrifying signal results on the bands.  

The system may work great, but buyer beware. 

73

Bob, K4TAX

On 5/2/2021 6:49 AM, Mark Morin wrote:
On Sat, May 1, 2021 at 08:01 PM, David Bunte wrote:
Bob -
 
I don't understand your statement "I guess this is typical of MFJ, attaining performance that flies in the face of laws of physics."
 
I only glanced at the item in the MFJ Catalog but did not see any claim that is patently false. They say the device combines the output of two amplifiers... I did not see a claim that it accomplished that without loss. Did you see a claim that I missed, or are you just choosing to bash MFJ?
 
Dave - K9FN

Dave, as soon as I saw this product, the first question that popped into my mind was losses. Transmitter combiners always have loss and it’s usually quite significant. I downloaded the very scant “manual”, which does not include any loss specification but it does say that you can obtain twice the power compared to a single amplifier. That statement implies zero loss, which is physically impossible. 

So I’m with Bob on this on. It looks and smells like snake oil to me. 

Mark VA2MM 


Virus-free. www.avg.com


Ken K6MR
 

I have not looked at the MFJ unit specifically, but it’s very easy to make an efficient coupler these days.  I ran the W6PQL coupler with two KPA500s for years and the “loss” was virtually unnoticeable.  Remember that all of the new two pallet solid state amps use a combiner.  The combiner I used was mounted in a closed aluminum box, and even running full power RTTY it barely got warm.  So it can be done.

 

Ken K6MR

 

From: K9MA
Sent: Sunday, May 2, 2021 08:52
To: Elecraft-K3@groups.io
Subject: Re: [Elecraft-K3] KPA500 Combiner - MFJ ACB-1000

 

Lack of active cooling suggests that the loss can't be large: a 1dB loss would be about 300 W.

 

The manual definitely should specify equal cable lengths.

 

73,

Scott K9MA 

----------

 

Scott Ellington

 

 --- via iPad



On May 2, 2021, at 7:53 AM, Bob McGraw - K4TAX <rmcgraw@...> wrote:



Combiners of and any form have loss.  Therefore using 2 amplifiers of equal power will not produce twice the power of one amplifier.  I'm not bashing MFJ, but I am disputing their written claims. 

If they specified using two identical amplifiers and the inputs were driven 180 degrees and then combined accordingly, this might make more sense as the combined power stage would be push-pull.  To be effective, the phase shift through the system would have to be maintained very carefully, including identical electrical lengths of input and output coax lines. 

I can visualize the use of conventional tube amps and there associated Tune and Loading circuits, not having identical phase relationships,  producing horrifying signal results on the bands.  

The system may work great, but buyer beware. 

73

Bob, K4TAX

On 5/2/2021 6:49 AM, Mark Morin wrote:

On Sat, May 1, 2021 at 08:01 PM, David Bunte wrote:

Bob -

 

I don't understand your statement "I guess this is typical of MFJ, attaining performance that flies in the face of laws of physics."

 

I only glanced at the item in the MFJ Catalog but did not see any claim that is patently false. They say the device combines the output of two amplifiers... I did not see a claim that it accomplished that without loss. Did you see a claim that I missed, or are you just choosing to bash MFJ?

 

Dave - K9FN

Dave, as soon as I saw this product, the first question that popped into my mind was losses. Transmitter combiners always have loss and it’s usually quite significant. I downloaded the very scant “manual”, which does not include any loss specification but it does say that you can obtain twice the power compared to a single amplifier. That statement implies zero loss, which is physically impossible. 

So I’m with Bob on this on. It looks and smells like snake oil to me. 

Mark VA2MM 

 

Virus-free. www.avg.com

 


Dan Roberts
 

Combining transmitters to increase power output is not new technology.  I was personally involved in a broadcast situation almost 50 years ago where we combined two 20 kW tube-type FM transmitters to make 40 kW.  About 15 years ago, I was involved in a situation where a 20 kW and a non matching 10 kW solid state transmitters were combined to make 30 kW.  Yes, it’s possible, but not for the average ham radio guy. The vast majority of broadcast transmitters these days are solid state and use multiple internal combiners to achieve high power.

 

I’m not dumping on MFJ.  I’ve bought lots of stuff from them over the years and their after-sale service has been above average. However, Bob is correct and they need to publish more information on this combiner beyond vague power limitation specifications, box size and SO239 connectors.  The schematic published in the downloadable “Instructions” simply shows two transformers and a 100 Ohm resistor of unknown wattage.  Nothing more.  No frequency limits are shown.  The power handling of that 100 Ohm resistor is very important, should there be a problem with one of the transmitters.  And, of course, no mention of how to properly install and manage a system of this sort.

 

This is an interesting piece of equipment.  It might work fine, given proper care is taken in putting the system together, but I wouldn’t be buying one until I got more information.

 

Dan – K9DR

 

Sent from Mail for Windows 10

 

From: Lou W7HV via groups.io
Sent: Sunday, May 2, 2021 6:23 AM
To: elecraft-k3@groups.io
Subject: Re: [Elecraft-K3] KPA500 Combiner - MFJ ACB-1000

 

Hah.  Yeah.  Dumping on MFJ is never out of style.  I always figured the more one knew and understood, the better use they'd get out of MFJ products. I have a few that have served me and met my appropriately set expectations for many years.  Coincidentally, I happened to notice MFJ has 14 full page ads in the May QST. That can be viewed in a number of ways, but MFJ is certainly helping pay for the publication of the mag.

 

Lou W7HV 

 


Joe Subich, W4TV
 

On 2021-05-02 11:51 AM, K9MA wrote:
a 1dB loss would be about 300 W.
Only if one is combining two US "legal limit" amplifiers which in
itself would make the combination illegal.

If combining two 800 W amplifiers - which is the more appropriate
application - a 1 dB loss is 160 Watts. However, the efficiency of
a well designed splitter/combiner is on the order of 95%+ (or around
-0.25 dB which is 80W for 2 x 800W amplifiers).

73,

... Joe, W4TV


On 2021-05-02 11:51 AM, K9MA wrote:
Lack of active cooling suggests that the loss can't be large: a 1dB loss would be about 300 W.
The manual definitely should specify equal cable lengths.
73,
Scott K9MA


Lou W7HV
 

Many amps will put out more than 1500W.  It's only transmitting in excess of 1500W PEP is prohibited. Combine two 1500W amps and keep the combined output to 1500W or less, and you're legal.


Colin Smithers
 

The manual shows a transformer hybrid combiner (which can indeed achieve low loss) and talks about requiring equal inputs. This is indeed very brave, as tuning and therefore phase differences between amplifier inputs and outputs, even if the outputs are equal amplitude, will result in considerable dissipation in the internal 100 ohm load.

 

I’m not sure they have mentioned clearly enough that the amplifiers must be fed with the same signal on the same band for it to work without dissipating huge internal power. A box that size (looking at the SO239) will not dissipate significant power. They do not mention how to feed the amplifiers to achieve this  (you will need another box like this though smaller). Also you could not use amplifiers of different model (unless you are unreasonably lucky), but this is more implied than stated. If one amplifier were to fail, or fail to switch in, the internal dissipation would be half of the working amplifier’s output.

 

Again as has been previously stated the 100-ohm internal load needs to be very manly to cope with all likely conditions.

 

73, Colin G4CWH

 

From: Elecraft-K3@groups.io [mailto:Elecraft-K3@groups.io] On Behalf Of Lou W7HV via groups.io
Sent: 02 May 2021 20:51
To: Elecraft-K3@groups.io
Subject: Re: [Elecraft-K3] KPA500 Combiner - MFJ ACB-1000

 

Many amps will put out more than 1500W.  It's only transmitting in excess of 1500W PEP is prohibited. Combine two 1500W amps and keep the combined output to 1500W or less, and you're legal.


Chuck Hill K0MV
 

Hi Colin,

I'll offer my take on this.

Reading the manual on the ACB-1000 power combiner.  It is meant to be used with the ALS-500 solid-state amplifier (1995 vintage) and the ASP-200 power splitter.  There is no statement that this power combiner is general purpose or claim it could be used with other equipment. 

A review of the schematic of the ALS-500 shows it is already using a power combiner with transistors to achieve its power output.  Considering this is only claimed to work with the ALS-500 and its limited operating range up to 21.6MHz, the phase shift between two ALS-500s is probably not serious, feedline length matching is for 15 meters at most and on a single desk co-located isn't an issue.  The ASP-200 and ACB-1000 are a means to continue to continue the paralleling of the power transistors except in different ALS-500 boxes, considering the limitations of 1995 vintage transistors. 

If something goes wrong, that 100 ohm could get fried--good point.  It'd be a shame if one fried their KPA500 as well. 

I'd recommend against using the ACB-1000 with two KPA500s, because it is beyond the recommended operation of either.  A detailed review of the KPA500 schematic could result in a different conclusion, though.

I do recommend simply getting a KPA1500.  Expensive though.  Paired with the K3s, it's a really sweet setup complete with ATU, automatic bandswitching, quick turnon.  Beats my old Alpha 76PA.

73,

Chuck K0MV


On 5/2/21 2:17 PM, Colin Smithers wrote:

The manual shows a transformer hybrid combiner (which can indeed achieve low loss) and talks about requiring equal inputs. This is indeed very brave, as tuning and therefore phase differences between amplifier inputs and outputs, even if the outputs are equal amplitude, will result in considerable dissipation in the internal 100 ohm load.

 

I’m not sure they have mentioned clearly enough that the amplifiers must be fed with the same signal on the same band for it to work without dissipating huge internal power. A box that size (looking at the SO239) will not dissipate significant power. They do not mention how to feed the amplifiers to achieve this  (you will need another box like this though smaller). Also you could not use amplifiers of different model (unless you are unreasonably lucky), but this is more implied than stated. If one amplifier were to fail, or fail to switch in, the internal dissipation would be half of the working amplifier’s output.

 

Again as has been previously stated the 100-ohm internal load needs to be very manly to cope with all likely conditions.

 

73, Colin G4CWH

 

From: Elecraft-K3@groups.io [mailto:Elecraft-K3@groups.io] On Behalf Of Lou W7HV via groups.io
Sent: 02 May 2021 20:51
To: Elecraft-K3@groups.io
Subject: Re: [Elecraft-K3] KPA500 Combiner - MFJ ACB-1000

 

Many amps will put out more than 1500W.  It's only transmitting in excess of 1500W PEP is prohibited. Combine two 1500W amps and keep the combined output to 1500W or less, and you're legal.


K9MA
 

It's also probably a bad idea to try to use a power combiner with internal ATU's in the amplifiers, unless you can make absolutely sure they both use the same settings. Better to use a single tuner AFTER the combiner.

73,
Scott K9MA

On 5/2/2021 4:41 PM, Chuck Hill K0MV wrote:

Hi Colin,

I'll offer my take on this.

Reading the manual on the ACB-1000 power combiner.  It is meant to be used with the ALS-500 solid-state amplifier (1995 vintage) and the ASP-200 power splitter.  There is no statement that this power combiner is general purpose or claim it could be used with other equipment. 

A review of the schematic of the ALS-500 shows it is already using a power combiner with transistors to achieve its power output.  Considering this is only claimed to work with the ALS-500 and its limited operating range up to 21.6MHz, the phase shift between two ALS-500s is probably not serious, feedline length matching is for 15 meters at most and on a single desk co-located isn't an issue.  The ASP-200 and ACB-1000 are a means to continue to continue the paralleling of the power transistors except in different ALS-500 boxes, considering the limitations of 1995 vintage transistors. 

If something goes wrong, that 100 ohm could get fried--good point.  It'd be a shame if one fried their KPA500 as well. 

I'd recommend against using the ACB-1000 with two KPA500s, because it is beyond the recommended operation of either.  A detailed review of the KPA500 schematic could result in a different conclusion, though.

I do recommend simply getting a KPA1500.  Expensive though.  Paired with the K3s, it's a really sweet setup complete with ATU, automatic bandswitching, quick turnon.  Beats my old Alpha 76PA.

73,

Chuck K0MV


On 5/2/21 2:17 PM, Colin Smithers wrote:

The manual shows a transformer hybrid combiner (which can indeed achieve low loss) and talks about requiring equal inputs. This is indeed very brave, as tuning and therefore phase differences between amplifier inputs and outputs, even if the outputs are equal amplitude, will result in considerable dissipation in the internal 100 ohm load.

 

I’m not sure they have mentioned clearly enough that the amplifiers must be fed with the same signal on the same band for it to work without dissipating huge internal power. A box that size (looking at the SO239) will not dissipate significant power. They do not mention how to feed the amplifiers to achieve this  (you will need another box like this though smaller). Also you could not use amplifiers of different model (unless you are unreasonably lucky), but this is more implied than stated. If one amplifier were to fail, or fail to switch in, the internal dissipation would be half of the working amplifier’s output.

 

Again as has been previously stated the 100-ohm internal load needs to be very manly to cope with all likely conditions.

 

73, Colin G4CWH

 

From: Elecraft-K3@groups.io [mailto:Elecraft-K3@groups.io] On Behalf Of Lou W7HV via groups.io
Sent: 02 May 2021 20:51
To: Elecraft-K3@groups.io
Subject: Re: [Elecraft-K3] KPA500 Combiner - MFJ ACB-1000

 

Many amps will put out more than 1500W.  It's only transmitting in excess of 1500W PEP is prohibited. Combine two 1500W amps and keep the combined output to 1500W or less, and you're legal.


-- 
Scott  K9MA

k9ma@...