BACK in the pre-historic times, when there were no transistors and only
tubes, the US had a power limit of 1000w Input Power.
P=Isq. R, or P=E/I were common formulas to use.
Let's take the second one.
We have a linear running 1000v and 500 mA of courrent.
Multiply 1000 x 0.5 = 500w input power
Now let's assume that amp is running in Class C mode.
Class C typically yields about 60% to 65% efficiency.
Let's go with 65%
65% of 500w Input Power = 325 Watts Output Power.
So is this a 500w amp or a 325w amp? That is Input vs. Output.
BUT, for SSB, we can't run class C (too much distortion).
So we must run perhaps class B.
Class A gets only about 50% efficiency, class B about 55%.
Let's say we were running that amp in class B (ssb).
55% X 500 = 275 watts (now that 500w input amp is in reality only a 275w
amp if we specify it in output power).
As a rule of thumb for estimating, it simply to take 50%.
A 1500w MFJ Matchbox rated for the old SSB rating system is really a 750w
matchbox.
Their 3000w Matchbox can handle 1500w if the SWR does not get too high.
Viola. Now you know.
73
Rick
-----Original Message-----
From: tentec-bounces@contesting.com [mailto:tentec-bounces@contesting.com]
On Behalf Of Richards
Sent: Thursday, December 01, 2011 12:25 PM
To: Discussion of Ten-Tec Equipment
Subject: Re: [TenTec] Jupiter Autotuner upgrade?
I must admit to not understanding what MFJ means by input power versus
output power. I figure output power is what comes out of the amp on the
way to the antenna, with the tuner in between... OK... but I don't get
what they mean by "amplifier input power" - which I have read in the
catalog descriptions.
It is just this sort of doubletalk that sent me to Palstar for a pair of
tuners.
My big stick has an 4:1 Un-Un made by DX-Engineering. It came with a
4:1 current balun that worked fine (the original balun was a 4:1
combination current balun and and RF choke design that is supposed to be
OK, but after Zero-5 was caught peddling the wrong type balun (a voltage
balun) from ArraySolutions, then Array Solutions got wise and quickly
supplied a proper Un-Un. There was some flap on this on qRZ.com where
some Dutch ham complained and the guys on the forum figured it out (He
re-wired his to the correct configuration and it worked swell after
that...) Soon thereafter, DX-Engineering came out with its 4:1 Un-Un.
Long story, but I was there all the way, and DX-Engineering
practically gave me the new design Un-Un because I was fairly prominent
in promoting the product on various web discussion groups.
Coincidence ? Yes, absolutely !
I like the guy at Balun-Designs. He made the one I use on my OCF
dipole. He and I had quite a nice discussion about where to put the
feed point in order to maximize performance on 15 meters, and lower
overall impedance to around 200 ohms (referencing our previous
discussion thereon.)
I agree that, if I were to try one of these newer MFJ tuners, I would
probably pick the legal limit model, and then only run about 500 - 600
watts at most, keeping everything conservative. I don't like to stress
the amp, either. It is not worth it, and does not really get you any
more S-meter units.
========================= JHR ================================
On 11/30/2011 9:53 PM, Rick - DJ0IP / NJ0IP wrote:
> What James, a Chinese product with quality issues?
> Are you serious?
> ;-)
>
> Now I'll be serious and say that the CG-2000 which is the low power
version
> MFJ is re-badging, in the meantime is shipping at a pretty good quality
> level. It wasn't always. That of course is no assurance that the bigger
> versions will have no quality issues. In fact my experience, having
worked
> with the Chinese a lot is that you have serious quality issues with every
> new product, much more so than we know it with new products made in our
own
> countries.
>
> Also, as Geoff pointed out earlier, these power ratings of 1500 and 600
are
> misleading and possibly bogus.
> Besides being subject to the same rules of all matchboxes, "when the SWR
is
> higher, you have to reduce power", we also need to understand if these new
> boxes are still rated with the "old" MFJ rating system of "SSB Input
Power".
> If so, then you can halve those power ratings immediately before you even
> unpack it. A straight forward question to MFJ tech support should get an
> answer to this, if you can get an answer from them.
>
> My hunch is that this unit is actually rated in output power because
that's
> how the CG-2000 and CG-3000 are rated.
> Just don't forget the bit about reducing power when the SWR is high.
>
> Now in its manual it says:
>
> Features
> . Automatically matches antennas from 12 to 1600 ohms impedance (SWR up to
> 32:1)
> . Handles 1500 watts SSB/CW
>
> Here it does not specify whether it is Input Power or Output Power.
> In the specifications section it is also vague.
> Unfortunately there is no schematic, so I could not see the voltage
ratings
> on the capacitors.
>
> The matchbox is rated to an SWR of 32:1, or 1600 Ohms.
>
> There is a long paragraph explaining how to add additional feedline
lengths
> when you get impedances which cannot be matched. Same as in every other
> matchbox's manual.
>
> So James, I guess the big question is, will your big stick present an
> impedance on any band which is above 1600 Ohms?
> I would suggest using a 4:1 Unun (I sourced one from Balun Desgins just
for
> this purpose). If you have a good 4:1 balun, you only have to re-solder
one
> wire and it's an Unun.
> You may find that you have to switch the unun out on some bands,
especially
> the low bands.
>
> Finally, being as you only run 600w anyway, you shouldn't have a problem
> with it, especially if you use an Unun where required.
>
> 73
> Rick
>
> -----Original Message-----
> From: tentec-bounces@contesting.com [mailto:tentec-bounces@contesting.com]
> On Behalf Of Richards
> Sent: Thursday, December 01, 2011 1:20 AM
> To: Clayton Brantley; Discussion of Ten-Tec Equipment
> Subject: Re: [TenTec] Jupiter Autotuner upgrade?
>
> MFJ has a new remote auto tuner that costs about $750 - supposed to
> handle 1500 watts. They have one that handles 600 watts for $400.
>
> Some of use with 43 foot monopole vertical antennas are waiting to see
> how the first user reviews look before we dive into an MFJ product. I
> suspect they are made by the same Chinese outfit that made similar
> tuners formerly sold by Array Solutions - but Jay Terleski the owner
> said they dropped the line over quality control issues. At that time,
> they had one that could handle 800 watts. I suspect (hope, actually)
> that if they are from the same manufacturer, they have been improved.
> Time, I suppose, will tell.
>
> ========================== JHR ==============================
>
>
>
>
>> From: Rick - DJ0IP / NJ0IP<Rick@DJ0IP.de>
>
> I think MFJ recently came out with one that can handle high power,
>> but I haven't seen it yet and don't know how much it costs.
>
>
> ===============================================================
>
>
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