Topband: NCC and phased Active verticals follow up
k7tjr at msn.com
Wed Oct 24 14:29:22 EDT 2007
Tod wrote: I inserted the jumper designed to enhance 160 meter operation and measured
the BC band signals and also the 1850 spur at the station end of the active
vertical. Here is what I found:
590 kHz = -35 dBm
1290 kHz = -18 dBm
1850 kHz = -80 dBm
The answer is to insert a band pass filter or a very good high pass
filter that has high rejection of frequencies in the BC band in the output
feed line of the active whip to reduce the out of band signals.
Thanks for sharing your success Tod as I am convinced that we have not seen the best out of these small arrays yet. It is these tid-bits of information that will advance the state of this art.
Just a word of caution for those that may want to try this on other arrays more complicated than 2 variably phased elements. Installing any inductor/filter on the input of a Hi-Z amp may cause some undesirable phase shifts, perhaps even amplitude shift. The phase shift could vary between different hi-z amps. It probably would not matter in something as forgiving as a 2 element or 4-square but might factor in when using really narrow array element spacing. Of course it would not when using a variable amplitude/phase shifting combiner. It would be imperative to know the phase shift tolerances of any Hi-Z preamps under different input filter arrangements if they were to be used in more complicated arrays. Also adding a BCB filter as Tod has suggested in each output line could insert a phase shift in each leg of an array which for only 2 elements as he is using would not matter but in other multi element arrays would need to be accounted for. Does any one know if DXE publishes amplitude and phase shift specs for their Hi-Z antenna/amplifier.
Lee K7TJR Oregon www.k7tjr.com
More information about the Topband