[Lowfer] more on preamplifiers

[Zack Widup]

On Thu, 1 Mar 2007, Jay Rusgrove wrote:

> Just a further note...
> 
> The preamplifier referenced in John's loop antenna article is much more robust in terms of 2nd and 3rd order IM distortion than the JFET preamplifier you are using. This means that his preamplifier might not overload itself, but it's possible the additional gain from the preamplifier could cause overload in the receiver. If it turns out to be receiver overload rather than preamplifier overload then a filter between the preamplifier and the receiver could work.
> 
> You can determine if overload is coming from the preamplifier or the receiver by temporarily inserting a 50 ohm attenuator ( 6 dB for example) between the preamplifier and the receiver. If the interference drops by an amount equal to the amount of attenuation the problem is in the preamplifier. If the interference drops by more than the amount of the attenuation (2 or 3 times the amount of the attenuation) the problem is in the receiver.
> 
> The aliens have descended.
> 
> Jay W1VD / WD2XNS

Thanks Jay (and others)! I am using a TS-850SAT as the receiver.  I MAY 
not even need a preamp with it; it has a lot of gain since I bypassed the 
bc band filtering they put into the rig. I have switched on and off the 
preamp (AIP) in the receiver and put in the 6 and 12 dB attenuators.  They 
didn't affect the problem, so I'm assuming it's from the preamp.  

I'll try removing the preamp this weekend and see how the loop performs 
without it.

I hope the aliens like coffee! I put on the coffee pot.  ;-)

73, Zack W9SZ