> 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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