I have little RF amplifier knowledge however I believe that your 66:1 SWR
comment is for pulsed service which has a much lower duty cycle than a
typical amateur radio transmission, especially the popular FT8 mode. A
higher duty cycle with high SWR creates more heat that needs to be
dissipated. A LDMOS can definitely fail, even on commercial amps with
protection circuits.
John KK9A
Sent via the Samsung Galaxy 7 edge, an AT&T 4G LTE smartphone.
On Tue, Mar 10, 2020 at 10:32 PM rjairam@gmail.com <rjairam@gmail.com>
wrote:
> LDMOS itself does not require perfect SWR. The older MOSFETS did. LDMOS do
> not. They can be operated at 66:1 SWR. This is a dead short at full output.
> There are videos of them arcing with them and welding. Probably not for
> extended duty cycle, but guess what- neither can your ceramic tube amp with
> tubes made of unobtainium.
>
> The fragile parts in a solid state amp that are affected by high SWR are
> the filter network, the capacitors and inductors.
>
> The software in modern amplifiers, if properly implemented will absolutely
> protect your amplifier and antenna system. If you throw high SWR it will
> shut down or fold back (de-rate).
>
> The KPA1500 has an internal antenna tuner that can handle up to 6:1 SWR.
>
> Other amplifiers such as the PGXL (which I have) can operate at high SWR
> with no tuner. I can run mine at 2.5:1 with software derating. I get about
> 1.3kw out of it at that high SWR. With about 3:1 SWR I can do about 500w
> depending on the band. Beyond that I get a fault. With 2:1 SWR I can do
> 1.5kW. There is a tuner being developed for that one as well. I don’t abuse
> it and I try to run my antennas resonant. I’ve had this amp since it was
> being alpha tested and run it through a variety of antennas and duty cycle.
>
> I also ran an Alpha 91B so I have an idea of what a tube amp can do. The
> solid state amps work well and in terms of SWR tolerance are pretty good.
> Elecraft and SPE did a very good thing by including built in antenna
> tuners. The SPE implementation is excellent as it follows CAT. From my
> limited use of the KPA1500 it seems To do the same thing.
>
> This is based on my actual experience and not assumptions.
>
> 73
> Ria, N2RJ
>
>
>
> On Tue, Mar 10, 2020 at 6:11 PM <john@kk9a.com> wrote:
>
>> Those are two completely different animals, one is lightweight and has
>> LDMOS finals that need an antenna tuner or a perfect antena and the
>> other uses a ceramic tetrode that can tolerate 3:1 SWR. A tetrode
>> tunes differently than a triode but perhaps the auto tune takes care
>> of this. I am not sure if there is an OM power list but there is an
>> Elecraft list where you can follow any issues or complaints that
>> people may have. Is quietness a concern? Is quickly setting it up
>> without a lot of adjustments a concern?
>>
>> FWIW, I have used an Acom 2000A several times and basically I just
>> plugged it in and it worked plus it's super quiet. The only issue I
>> have saw with this amp is that it is sensitive to arcs in the antenna
>> system.
>>
>> John KK9A
>>
>>
>>
>> K4XS wrote:
>>
>> Looking for a backup amp for the new station. Probably going to run
>> SO2R so auto-tune is important. I'm running a K3S and the second
>> radio will also be a K3S. I really don't care if the amp "matches"
>> the K3S in looks. Like most of you guys I'm concerned about
>> performance. Both rigs are equal in price.
>> Here's the question: If you were buying a new amp and were buying it
>> to satisfy the above criteria, which would you choose and why?
>> K4XS
>>
>>
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>>
>
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