MavamQ
Member
Hi all,
I just a recently erected superloop terminated with 910Ω.
I just finished a test comparing the use of an
amp to using just a 9 to 1 transformer.
The amp consists of a Lankford 2 FET amp,
This amp has a high input impedance so does not load the 900Ω antenna, this a 6db voltage gain over transformer that matches the load.
A matching transformer causes a 6db voltage loss compared to a an amp with high input impedance.
Then a 900Ω to 100Ω transformer has 3 to 1 voltage stepdown, that is another 9.5db voltage loss.
6db + 9.5db = 15.5 db. Meaning a high input amp already has 15.5db over the use of a matching transformer.
and a Norton Noiseless Feedback (NNF) amp setup for about 11db gain.
With the NNF gain of 11db plus the 15.5 db, I would expect 26.5 db of signal over the use of
a matching transformer. After logging signal strength of 20 stations with the transformer and then amp,
then using an attenuator in the feedline, I reduced the signal to equal the transformer signal strength.
I needed to add between 20 and 25 db of attenuation to get the signal equal. Mostly it was 22db.
That's close, to 26.5, however do you any thoughts about where the other 4db went?
Ya, I know signal to noise is the issue, but, the amps are supposed to be low noise,
and I don't notice any difference, but, then I don't notice any audible difference between an
S6 signal and an S9 signal.
I have an SDR in my future to see such things.
Thank, Mikek
I just a recently erected superloop terminated with 910Ω.
I just finished a test comparing the use of an
amp to using just a 9 to 1 transformer.
The amp consists of a Lankford 2 FET amp,
A matching transformer causes a 6db voltage loss compared to a an amp with high input impedance.
Then a 900Ω to 100Ω transformer has 3 to 1 voltage stepdown, that is another 9.5db voltage loss.
6db + 9.5db = 15.5 db. Meaning a high input amp already has 15.5db over the use of a matching transformer.
and a Norton Noiseless Feedback (NNF) amp setup for about 11db gain.
With the NNF gain of 11db plus the 15.5 db, I would expect 26.5 db of signal over the use of
a matching transformer. After logging signal strength of 20 stations with the transformer and then amp,
then using an attenuator in the feedline, I reduced the signal to equal the transformer signal strength.
I needed to add between 20 and 25 db of attenuation to get the signal equal. Mostly it was 22db.
That's close, to 26.5, however do you any thoughts about where the other 4db went?
Ya, I know signal to noise is the issue, but, the amps are supposed to be low noise,
and I don't notice any difference, but, then I don't notice any audible difference between an
S6 signal and an S9 signal.
I have an SDR in my future to see such things.
Thank, Mikek
