The point I responded to was the statement that some amps fold-back with
very low SWR's. Clearly the use of an antenna tuner was not included.
The fact that most (not all) SS Amps have Automatic Antenna Tuners just
reinforces my statement.
It may take some innovative fellow to come up with a SS Amp that behaves
better and my mention of LDMOS devices may be the way to go.
Some of the newer LDMOS devices are quite robust, and seem to be
oblivious of SWR (to a point).
Clearly, the Tube Amp beats any of the SS Amps today, hopefully that will
change in my lifetime.
73, Dick, W1KSZ
On Sat, Oct 26, 2013 at 6:23 PM, Roger (K8RI) on TT <
K8RI-on-TowerTalk@tm.net> wrote:
> On 10/26/2013 3:34 PM, Richard Solomon wrote:
>
>> That just shows the failings of SS Amps. A 1.3:1 SWR equates to 1.7%
>> reflected power. Any
>> Amp that can't handle that has no place in my shack.
>>
>
> I disagree. It's not a fault in the amp. Your and my tube amp "have tuners
> built in" called a PI or PI/L network that matches the high plate impedance
> to the low impedance of the antenna system. If you put the equivalent tuner
> at the output of the SS amp it too will operate into a wide range of
> impedances.
>
> When operated into a low SWR the SS amp doesn't need a tuner.
>
> The short comings of the SS amp are not an inability to operate into a
> high SWR, but rather the fragility of solid state devices. Where a tube can
> swallow a voltage spike, even one lasting a tiny fraction of a second will
> render the SS device inoperative. The same is true of exceeding the
> dissipation rating of the device. Most tubes used in QRO have a lot of
> mass, presenting a large thermal inertia while even power transistors have
> a die with a mass of a few grams, hence little or no tolerance for
> excessive dissipation.
>
> SS amps require sophisticated and fast protection from, voltage, current,
> over drive, temperature and SWR. As was mentioned, when they are operated
> into a load that is not closely matched IM products go up and the power
> goes down. If you ran a tube amp with the output impedance fixed, wouldn't
> it do the same or similar?
>
> Many of today's hams have trouble properly tuning and operating Tetrode
> amps resulting in increased IM products. A given tube also, usually has a
> plate voltage where IM products are minimized. Granted, Triodes are a
> little easier to tune, but more than a few abuse the tubes in those as
> well. However, many tube amps now come with much the same protection as do
> SS amps, when in the old days you "might" find a glitch resistor. Even
> "top end amps" back then had little more than a circuit breaker for the AC
> power source. It was up to the operator not to blow the grids out of those
> Hallicrafters and Collins amps. Whether Triode or Tetrode, protective
> circuitry was pretty much non existent.
>
>
>
>> As for tube amps, just shows the benefits of a tuneable Pi-Network.
>>
>> I am surprised the Quadra was that bad.
>>
>
> I think you will find that SS QRO amps are all quite similar in tolerating
> SWR although devices are becoming more rugged. OTOH many of the high power
> and SWR handling are for pulse service rather than for CW and SSB, let
> alone, digital.
>
> Even with my QRO amp, I use a VNA through a tuner to match the antenna
> system so the rig sees a very low SWR.
> I use an A/B switch, select the bar graph tune function and match the
> system to a very low swr QUICKLY. I then tune the amp into a dummy load
> knowing the settings ahead of time. A tune up only takes a few seconds.
>
> With this approach the using a SS amp would be little different than the
> tube amp except for not needing the extra tuning step.
>
>
> 73
>
> Roger (K8RI)
>
>
>> 73, Dick, W1KSZ
>>
>>
>> On Sat, Oct 26, 2013 at 12:03 PM, Mark Robinson <markrob@mindspring.com
>> >wrote:
>>
>> I looked at the LPDA and wasn't impressed by the front to back ratio, so
>>> I
>>> installed an Optibeam OB11-5. I have been very happy with it.
>>>
>>>
>>> Mark N1UK
>>>
>>>
>>> ----- Original Message ----- From: "Pete Smith N4ZR" <
>>> n4zr@contesting.com>
>>> To: <towertalk@contesting.com>
>>> Sent: Saturday, 26 October, 2013 2:19 PM
>>>
>>> Subject: Re: [TowerTalk] Tower and antenna decisions
>>>
>>>
>>> My Yaesu Mark 5 would begin to roll back its power output over about
>>>
>>>> 1.8:1. What really bugs me about LPDA's is the terrible tradeoff
>>>> between
>>>> weight and size and gain/directivity at any given frequency.
>>>>
>>>> 73, Pete N4ZR
>>>> Check out the Reverse Beacon Network at
>>>> http://reversebeacon.net,
>>>> blog at reversebeacon.blogspot.com.
>>>> For spots, please go to your favorite
>>>> ARC V6 or VE7CC DX cluster node.
>>>>
>>>>
>>>> On 10/26/2013 1:56 PM, steve jobes wrote:
>>>>
>>>> Rick I disagree with your statement. As a owner of a Tennadyne T-10 and
>>>>> currently a T-12 your statement is flat out wrong. I swept my T-12
>>>>> with my
>>>>> rig expert AA-230 analyzer and it was below 2-1 across the 13-30 mhz.
>>>>> range. Not sure what you are talking about, OR WHAT BRAND. But to say
>>>>> mediocre SWR is a false statement.
>>>>>
>>>>> 73,
>>>>> Steve W1DXH
>>>>>
>>>>>
>>>>> -----Original Message-----
>>>>> From: Richard (Rick) Karlquist <richard@karlquist.com>
>>>>> To: towertalk <towertalk@contesting.com>
>>>>> Sent: Fri, Oct 25, 2013 7:25 pm
>>>>> Subject: Re: [TowerTalk] Tower and antenna decisions
>>>>>
>>>>>
>>>>>
>>>>> I briefly looked at log periodics and one thing
>>>>> that hasn't been discussed here is the mediocre
>>>>> SWR of LPDA's. You're pretty much going to have
>>>>> to use a tuner, and you also have increased feedline
>>>>> loss. Might work for some users, but I'm sticking
>>>>> with my SteppIR antennas (3 of them so far).
>>>>>
>>>>> An LPDA would however, make a good broadband receive
>>>>> antenna for a skimmer, if you want to optimize
>>>>> one direction.
>>>>>
>>>>> Rick N6RK
>>>>> ______________________________****_________________
>>>>>
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>>>>> >
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>>>>>
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