[Antennas] Create log periodic antenna question

[Michael Josefsson]

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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