>>// 10MHz requires a bandswitch with an additional contact because 10MHz
>>is too far from from 7MHz or 14MHz to allow sharing bands -- such as
>>12m/10m.
>
>Very untrue. The SB-200 will tune up quite nicely on 30 meters in stock
>form, just like it does on 17 and 12 using the 15 and 10 meter band spots. I
>do not remember which band was better, 7 or 14 mhz, but she will tune up
>there with ease.
>
// Surely. My SB-220 tunes up on 30m when the bandswitch is either on
the 40m or 20m position. However, there are tradeoffs. When the
bandswitch is on the 40m position, there is too much L, so the Q is c. 7
- which limits the ability of the tank to match the load. When the
bandswitch is on the 20m position and the driving signal is on 30m,
operating Q goes to the other extreme -- i.e., up. Increased Q is good
for the tank's abilty to match, however, even though the Tune-C and
Load-C have enough capacitance to tune up, the tuning is sharp and the
tank's circulating current is c. 40% higher. This may not sound like a
big thing, but 40% more current means a doubling of the I^2 loss in the
bandswitch contacts. Admittedly, doubling the heat dissipated in the
bandswitch is probably not a biggie for those who enjoy working on
amplifiers, like surprises, and have an abundance of spare bandswitches.
Yet another problem is input mismatch.
cheers, Lane
>
>>
>> >Any instruction available? Also interested to add
>> >1,8MHz. All hints are very welcome!
>> >
>>// 1.8MHz is difficult to add to a SB-200 because, unlike the SB-220,
>>there is not much room for the added L, Tune-C, and Load-C padders.
>>
>>cheerio, Jukka
>>
>>- R. L. Measures, 805.386.3734,AG6K, www.vcnet.com/measures.
- R. L. Measures, 805.386.3734,AG6K, www.vcnet.com/measures.
end
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