[Antennas] Create log periodic antenna question

Mon Jun 2 07:00:11 EDT 2008

Hi Y S!
If all the elements are ok and connected properly then perhaps the 
test setup is the culprit? The logperiodic should work just fine in a 
vertical orientation and would even in this orientation give a 
substantial gain. Some possible causes in random order... (just 
guessing here as I do not know anything about your setup)
If the two antennas are close to each other there might be a detuning 
effect between the antennas. As the vertical is rather imperviuos to 
detuning, the more sophisticated logperiodic can get much more 
"confused". Likewise, metal structures at close distances will have a 
negative effect. A log-periodic is more of a "tuned instrument" than 
the raw vertical.
Are the test frequency used within the antenna's specification?
The test-transmitter must be located quite a long way away to let the 
far field get established. A distance of 5-10 wavelengths is a 
minimum. Perhaps a broadcast station can be used as a distant and 
stable signal source?
The log-periodic's lobe might be higher than the vertical's if the 
latter has a very good ground system. This would result in better low 
take-off angle response for the vertical.
If you tell us a bit more about your setup (physical distances, 
ground, frequency/ies used, SWR, how you measure signal strength etc) 
then you may get a more precise answer.
/Micke SM5JAB
On 2 jun 2008, at 09.26, Y S Lee wrote:
> Hello;
> I recently obtained an used Create 5130-2N logperiodic antenna
> from a local ham. I installed the antenna vertically and compared 
> receiving signal
> strength with a vertical antenna. The vertical antenna showed better 
> signal
> strength than the log periodic pointing to a transmitting station. 
> This
> did not make sense because the log periodic antenna is supposed to
> have higher gain. Changing cable did not make any difference.
> So my conclusion is that something must be wrong with the log 
> periodic.
> I checked all element connections and the connector and all seemed 
> fine.
> Any opnion what could be wrong?
> de HL1FB/WW6N
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