[TenTec] OmniVI Plus Over Drive Amp

[Ken Brown]

Okay Jerry, I'll try it. Since we were talking about a Ten-Tec Hercules 
II amplifier, what frequency between 1.8 and 29.7 MHz would you suggest 
I try, in order to see the most significant effect of two Bird 43s 
cascaded on a 50 ohm feed line into a 50 ohm non-inductive inductive 
load? I could use a  500H element, since I have one, and that seems 
appropriate for a Hercules II. Yet since Jim was talking about using a 
250H, and I also have one of them, I'll have to suffer the consequences 
of the more tight coupling of the sensitive 250 watt element. Then, 
running only 250 watts from the Hercules II, I'll have half as much 
reflected to look for.

The manual for the Bird 43 says the insertion VSWR is less than 1.05. 
The chart in the manual indicates 0.06% reflected power at VSWR of 1.05, 
so I'll expect to see less than 500 * 0.0006 = 0.3 watts reflected by 
the second Bird 43, back to the first Bird 43. (Or 0.15 watts if I'm 
using only 250 watts) If I see more than that, and the second meter is 
indicating almost zero reflected from the termination, I'll conclude 
that Bird has made a mistake in their specifications for the Bird 43. 
Three tenths of a watt might be difficult to see using the 250 watt 
element. The lowest power HF element I have is the 50H. If I use that to 
measure the reflected on the meter closest to the source, I should be 
able to see 0.3 watts, as the first hash mark on the 50 watt scale is 1 
watt. The tight coupling of that 50 watt element should not have any 
detrimental effect on the SWR on the feed line, including the second 
Bird 43, between the first Bird 43 and the termination.

I'll also have to factor in the specified accuracy of the Bird 43, which 
is +/-5% of full scale power. Using the 50 watt element that is +/- 2.5 
watts. So any reading below 0.3 + 2.5 = 2.8 watts reflected, between the 
second and third marks on the meter scale, will be acceptable. (Or at 
the 250 watt level 0.15 + 2.5 = 2.65 watts reflected, still in between 
the second and third marks)

I'll post my results when I have finished the test.

DE N6KB


>> The input Z of a Bird 43 feeding a matched load is also a matched load, 
>> as long as we are talking about a 50 ohm impedance system. The input Z 
>> of a Bird 43 feeding an unmatched load is an unmatched load, and that 
>> load is not the same Z as without the Bird in line. Just like any added 
>> length of feed line when there is significant SWR on the line, the Z 
>> changes along the line.
>>     
>
> Try two birds in cascade before you are so sure.
>
>   
>