Where do I start?

[bubbablitz]

When using one of these, and calculating Mhz/Length for VHF public safety band, where do I start measuring? Do I start at the bottom of the connector, or above the base? Also, do I collapse from the top or bottom, or does it matter. Thank You and Merry Christmas.

 

[Delta2_Coms]

My suggestion is to start measuring from the top of the base, which is part of the connector. The outer part of the connector is shielding the actual antenna element in that section, so it should not count in the antenna length...unless the manufacturers instructions dictate otherwise. I'm not sure of the internal construction of the antenna.

As for collapsing from the top or bottom, I would start collapsing from the top. This will keep the antenna's taper as smooth as possible, which is better for both reception and overall strength.

These things being said, in the end you probably won't notice much of a difference in reception no matter where you start measuring or collapsing from.

-All the Best

 

[mmckenna]

For receiving, it's not super critical.

But, you'd start from the top of the BNC connector, where the antenna element starts. Below that it's shielded and considered part of the feed.
Measure up from that point.

As for collapsing the sections...
A thicker antenna element will have more bandwidth (usable resonate frequency width), so collapsing from the top may have some slight improvement, but at that point you are really splitting hairs.

An antenna on top of a portable radio at anything below around UHF frequencies is going to suffer due to the lack of a suitable counterpoise (the 'other half' of the antenna).

 

[bubbablitz]

For receiving, it's not super critical.

But, you'd start from the top of the BNC connector, where the antenna element starts. Below that it's shielded and considered part of the feed.
Measure up from that point.

As for collapsing the sections...
A thicker antenna element will have more bandwidth (usable resonate frequency width), so collapsing from the top may have some slight improvement, but at that point you are really splitting hairs.

An antenna on top of a portable radio at anything below around UHF frequencies is going to suffer due to the lack of a suitable counterpoise (the 'other half' of the antenna).

 

[bubbablitz]

Thank You.