[AMPS] In Search Of: The Nearly Perfect T-R Switch

[Jim]

I have used the Ameritron QSK in a Heathkit SB-1000.  The only drawback that
I had found is that the MOS FET would short. This happened on way to many
occasions.

I would consider another Ameritron unit if the reliability was improved.
Is there a improved version ?  How about mods to the old version.

What about using the QSK-5 or RTTY contesting at 1500 watts output with a L
O N G cq. What about RTTY rag chewing at 1000- 1300 watts out for 10 minuets
?

Thanks and I am certainly enjoying the PIN diode discussion.

Jim W7RY


-----Original Message-----
From: Tom Rauch <w8ji@contesting.com>
To: Phil Clements <philk5pc@tyler.net>; amps@contesting.com
<amps@contesting.com>; Jim <jdc@ieway.com>
Date: Tuesday, July 06, 1999 2:11 AM
Subject: Re: [AMPS] In Search Of: The Nearly Perfect T-R Switch



>     IMHO, the use of mechanical relays for T-R switching modern radios and
>     amplifiers is about 10 years behind the times. The PIN diode T-R
>     switch introduced by Heath for the SB-1000 amp, and later produced by
>     Ameritron as the QSK-5 is using old hardware and technology.

The Ameritron switch came first.

>     was challenged by an article in QST some years back to use newly
>     available, much more robust PIN diodes in their products.

Ameritron was challenged publicly by a salesman who sells PIN
diodes to use the diodes his company made, even though they
were ten times the cost of diodes used and had a shorter carrier
lifetime.

Car salesmen challenge me to buy new cars all the time, like the
"spy under your seat" feature. Doesn't mean it's a good deal.

>     this up by calling Ameritron and asking if they had plans to modernize
>     the QSK-5. The guy I talked to at the time said Ameritron had no plans
>     to make any upgrades in the unit, which proved to be true, as there
>     have been no changes to this date in the QSK-5. Their only upgrade
>     available is a fan to supposedly increase the power handling
>     capability.

The fan is necessary in the outboard box because it has no airflow
at all. It is not necessary in a PA, where the board has airflow.

>     In the mid '80's, an outfit called Design Electronics Ohio, out of
>     Groveport emerged with a product called the QSK-1500.( Does anyone
>     know what happened to these folks?)

Designed with telephone help from me. It used half the diodes but
diodes of the same type as used by Ameritron.

>     Phil Pesavento developed the QSK-3000, using the new Macom 4P902-985
>     PIN diodes. These diodes were apparently very robust, as the technical
>     manual describes that they are installed on the board with wrenches!
>     (Has anyone ever heard of Macom, especially where to purchase these
>     diodes?)

Get your wallet out. Rather than use those diodes, I'd use vacuum
relays. You could buy a lifetime of vacuum relays for one P902.

With a quad of smaller diodes in parallel, you could handle the
same power at 10% of the cost. Every time you double the number
of diodes, you multiply power rating by a factor of at least four.

Four 500 watt 50 ohm load HF rated diodes in parallel on the
transmit line will conservatively handle 8 kW, and cost about 10
dollars wholesale. A single stud mount to do the same thing would
cost 50 dollars. Which would a smart person use?  Which one
would a salesman on commission try to sell the manufacturer?


73, Tom W8JI
w8ji@contesting.com

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