[TowerTalk] Tower and antenna decisions

Sat Oct 26 21:23:01 EDT 2013

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 at 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 at contesting.com>
>> To: <towertalk at 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 at karlquist.com>
>>>> To: towertalk <towertalk at 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
>>>> ______________________________**_________________
>>>>
>>>>
>>>>
>>>> ______________________________**_________________
>>>> TowerTalk mailing list
>>>> TowerTalk at contesting.com
>>>> http://lists.contesting.com/**mailman/listinfo/towertalk<http://lists.contesting.com/mailman/listinfo/towertalk>
>>>>
>>>>    ______________________________**_________________
>>>>
>>>>
>>>>
>>>> ______________________________**_________________
>>>> TowerTalk mailing list
>>>> TowerTalk at contesting.com
>>>> http://lists.contesting.com/**mailman/listinfo/towertalk<http://lists.contesting.com/mailman/listinfo/towertalk>
>>>>
>>>>
>>> ______________________________**_________________
>>>
>>>
>>>
>>> ______________________________**_________________
>>> TowerTalk mailing list
>>> TowerTalk at contesting.com
>>> http://lists.contesting.com/**mailman/listinfo/towertalk<http://lists.contesting.com/mailman/listinfo/towertalk>
>>>
>> ______________________________**_________________
>>
>>
>>
>> ______________________________**_________________
>> TowerTalk mailing list
>> TowerTalk at contesting.com
>> http://lists.contesting.com/**mailman/listinfo/towertalk<http://lists.contesting.com/mailman/listinfo/towertalk>
>>
> _______________________________________________
>
>
>
> _______________________________________________
> TowerTalk mailing list
> TowerTalk at contesting.com
> http://lists.contesting.com/mailman/listinfo/towertalk