[TowerTalk] Was "43ft Vertical Feeding Question and Balun Type"

[Ian White GM3SEK]

jimlux Wrote:

>Richards wrote:
>>>I just wish someone made a full gallon rated, self contained and 
>>>powered, automatic remotely operated antenna tuner.
>
>> Yes - I would buy one immediately and install it on my vertical.
>>
>>          (Marketing gurus pay attention!)
>>
>How much would you be willing to pay for this?
>
>The SGC 500W tuner is, as I recall, about $1500.. the Palstar 1500W
>autotuner is $1200, but not exactly designed for driving a vertical, nor
>is it in a weatherproof box.. The LDG is similar.
>
>If you're willing to do some fabrication one could probably cobble a
>solution up for around $2K (box, remote controls, etc.)
>
>A turnkey solution (like a kilowatt SGC equivalent) would probably be
>around $2500, if it were a product.  If you pay someone to design and
>integrate it from what's available today, figure more like $3-3.5.
>

Perhaps something like this: ebay item # 330287848331
The photographs in this listing show the type of construction that is 
required.

(For complete disclosure, I do know the seller, and some years ago 
bought one of the 1kW Racal auto-tuners from him. To avoid a  bidding 
frenzy from the USA, please note that it's local pickup only, in 
England.)

The main part of the manufacturing cost is obviously the QRO RF 
components and the enclosure. If anyone had the nerve to do it, they 
could buy a cheap QRP auto-tuner and substitute all the relays, 
inductors and capacitors. That would give the best of both worlds - high 
power handling with all the 'smarts' of a modern frequency agile 
auto-tuner.

The higher power requires some additional control logic that a 
lower-power ATU wouldn't need. To prevent damage due to hot-switching at 
high power, the ATU controller must automatically disable the PA while 
tuning-up. For example, the Racal units tune at 10-40W, which the relays 
can hot-switch without damage. These precautions also prevent damage to 
the PA and transceiver while tuning. When tuning is complete, the RF 
sampler in the ATU must also be switched out of line to avoid burning 
out the diodes.

The second problem area is the enclosure. It needs to keep everything 
dry in condensing atmospheres, but it also needs to remove the waste 
heat from internal RF losses. The massive finned metal case of the Racal 
ATUs is not just to make them rugged - its main purpose is to act as a 
giant heat sink. The units are hermetically sealed with a silica gel 
capsule to keep the air dry, and one of the photographs shows that some 
of the relays and capacitors are also encapsulated in silicone rubber to 
prevent arcing when using high power into very unfavorable loads.

All of these problems could be overcome if a resourceful individual is 
willing to shop around for one-off surplus parts. However, that route is 
not open to manufacturers, which explains why the commercial units are 
so expensive.


-- 

73 from Ian GM3SEK