[TowerTalk] HP8761A

[Michael Tope]

jimlux wrote:

>Roger (K8RI) wrote:
>  
>
>>jimlux wrote:
>>    
>>
>>>John Kemker wrote:
>>> 
>>>      
>>>
>>>>Yeah, that's why I'm asking others about it.  It's only rated for 
>>>>10W, but has a 5kW peak?  That's an interesting spread.  I wonder why 
>>>>the large range between nominal rating and peak rating?
>>>>
>>>>    
>>>>        
>>>>
>>>The average rating is determined by heating.  The peak rating is 
>>>determined by voltage breakdown.
>>>  
>>>      
>>>
>>Unless I'm missing something,  this would render the peak rating 
>>meaningless for almost all amateur use  Even SSB  at 100 watts PEP  is 
>>going to be pushing the 10W average unless making short transmissions. 
>>About the only thing I can think of that might work would be short 
>>pulses of high speed digital.
>>    
>>
>
>You're probably right.
>
>There are a variety of non-ham applications where the distinction is 
>important.  For instance, maybe you have a system which has some sort of 
>automatic shutdown, which might burp out high power pulses before the 
>automatic shutdown takes over. You'd have to know things about the 
>thermal time constant, etc.
>  
>
The 10 W average rating is probably worst-case at 18GHz where according 
to the data sheet the insertion loss can be as high as 0.8dB. That's 
equivalent to 1.7 watts dissipation with 10 watts input. Insertion loss 
at lower frequencies is going to be much better than that, so I wouldn't 
be surprised if the switch reliably carries 100W CW at VHF and UHF 
frequencies. OTOH, the relay contacts are probably very small in order 
to maintain good VSWR and isolation at 18GHz. This presumeably limits 
power handling compared with larger relay contacts whose VSWR and 
isolation would be unacceptable at 18 GHz.

73,  Mike W4EF....................