[TowerTalk] Antenna loads for bench testing

[jimlux]

On 2/15/19 3:37 PM, Richard (Rick) Karlquist wrote:
> 
> 
> On 2/15/2019 2:01 PM, n0tt1 at juno.com wrote:
> 
>>
>> The question is, if a builder wants to make "loads" for bench testing
>> (to simulate the actual antenna feed point impedances), how is the
>> negative
>> load resistance simulated?  If there is, say an impedance of -27 + j3.0
>> Ohms,
>> does the builder just ignore the negative sign of the resistive part of
>> the load
>> and use a 27 Ohm resistor in series with the required amount of inductive
>>
>> reactance or what?
>>
>> Thanks,
>> Charlie, N0TT
> 
> No, you definitely can't ignore the sign of the resistance.
> 
> See this construction article about how to realize a negative RF 
> resistance:
> 
> http://www.vk6fh.com/vk6fh/lambda_diode.htm
> 
> VK6FH shows how to use this to make a "Tunnel Dipper"
> without the tunnel diode, but you can repurpose.
> 
> Rick N6RK

I'm not sure you can build a negative resistance antenna simulator with 
that.. it's negative "dynamic resistance" (small increase in voltage is 
small decrease in current), but still positive overall.  I suppose you 
can AC couple it, and then your circuit has to work at RF.

Another approach is use an amplifier, but that has all sorts of 
complexities too - one could probably get it to work in steady state at 
a single frequency.