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Jimmy

Lectro whips - How does the length affect performance / frequencies?

11 posts in this topic

#: 1   Posted

Other than indicating the block, how does the length affect the performance? For instance the difference in length between a block Block 21 whip and a Block 25 whip is about an inch. Does this inch really make a difference in the frequencies the transmitter can access? I'm assuming it does and if so, how? I've always wondered this. Thanks!

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#: 2   Posted

The length of the whip is calc'ed to be optimal for transmitting and receiving the freqs in the band the equipment is in.  Yes, it makes a difference, especially at the edge of range.

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#: 3   Posted

1 hour ago, Jimmy said:

Other than indicating the block, how does the length affect the performance? For instance the difference in length between a block Block 21 whip and a Block 25 whip is about an inch. Does this inch really make a difference in the frequencies the transmitter can access? I'm assuming it does and if so, how? I've always wondered this. Thanks!

The short answer is "wavelengths."

However, it would appear you haven't "wondered this" enough to do even some basic internet research.  There are dozens, more likely hundreds, of web sites that contain information about the whys and wherefores of antenna design -- even past discussions on this site about the topic.

Study some of these and then come back with any specific questions.

I wouldn't venture onto a web site by, and for, doctors and ask, "Surgeries have always interested me. How do you choose each of the tools you use?"

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#: 4   Posted

how does the length affect the performance? For instance the difference in length...is about an inch. Does this inch really make a difference...I'm assuming it does and if so, how?


An inch makes a big difference in performance. However, I've learned that girth is just as, if not more, important.


Sent from my iPad using Tapatalk

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#: 5   Posted

Most antennas are cut to be optimal at the center frequency of the specific block they are meant for. If a block is say 500Mhz to 550Mhz the antenna is cut for 525Mhz. The closer to the center frequency that you can tune to the better your results should be.

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#: 6   Posted

In 2010, over several issues of the 695 Quarterly (now Production Sound and Video), I conducted some tests of antenna performance. I attempted to make comparisons that would reveal the advantages of various designs and identify exactly how much one type might outperform another. The results were generally instructive but trying to plot exact antenna performance is rather like trying to measure smoke. While patterns were discernible, a "weak" design would sometimes "hit above its weight" and confound expectations.

I made the first tests and set the groundwork for subsequent investigations in the Spring 2010 issue:

http://www.local695.com/Quarterly/695QuarterlyPDFs/695-Quarterly-2010-Spring.pdf

(The early issues were archived only as full issues and not broken down by article.)

As part of those tests, I mounted a cut-down whip on a transmitter to investigate how much range might be lost using the "wrong" antenna. The cut-down whip was about 1/2 the length specified for that radio. Always remembering the caveat that individual test runs are not necessarily indicative of future performance (sounds like the disclaimer of a stock broker), these were some results using proper length and cut-down antennas:

Range using an SMQV at 50mW output with standard whips on the receiver:

standard whip -  562 feet (receiver 8 feet above ground)
cut-down whip - 358 feet

standard whip -  518 feet (receiver 4 feet above ground)
cut-down whip - 300 feet

Range using an SMQV at 50mW output with SNA 600 antennas on the receiver:

standard whip  - 570 - 752 feet (distance to first isolated "hit" - end of range)
cut-down whip - 390 feet

standard whip  - 670 - 743 feet (distance to first isolated "hit" - end of range)
cut-down whip - 381 feet

Half the proper length is a considerable deviation from ideal. As Larry Fisher of Lectrosonics has often said, in the best circumstances a bent and rusty coat hanger will function just fine as an antenna. But, under challenging circumstances careful attention to detail is likely to pay dividends. 

David

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On 5/8/2017 at 0:17 PM, Christopher Salazar said:

 


An inch makes a big difference in performance. However, I've learned that girth is just as, if not more, important.


Sent from my iPad using Tapatalk

 

.....and that's how you make a dull thread more interesting !!!

thumbs up!

On 5/8/2017 at 8:50 PM, David Waelder said:

In 2010, over several issues of the 695 Quarterly (now Production Sound and Video), I conducted some tests of antenna performance. I attempted to make comparisons that would reveal the advantages of various designs and identify exactly how much one type might outperform another. The results were generally instructive but trying to plot exact antenna performance is rather like trying to measure smoke. While patterns were discernible, a "weak" design would sometimes "hit above its weight" and confound expectations.

I made the first tests and set the groundwork for subsequent investigations in the Spring 2010 issue:

http://www.local695.com/Quarterly/695QuarterlyPDFs/695-Quarterly-2010-Spring.pdf

(The early issues were archived only as full issues and not broken down by article.)

As part of those tests, I mounted a cut-down whip on a transmitter to investigate how much range might be lost using the "wrong" antenna. The cut-down whip was about 1/2 the length specified for that radio. Always remembering the caveat that individual test runs are not necessarily indicative of future performance (sounds like the disclaimer of a stock broker), these were some results using proper length and cut-down antennas:

Range using an SMQV at 50mW output with standard whips on the receiver:

standard whip -  562 feet (receiver 8 feet above ground)
cut-down whip - 358 feet

standard whip -  518 feet (receiver 4 feet above ground)
cut-down whip - 300 feet

Range using an SMQV at 50mW output with SNA 600 antennas on the receiver:

standard whip  - 570 - 752 feet (distance to first isolated "hit" - end of range)
cut-down whip - 390 feet

standard whip  - 670 - 743 feet (distance to first isolated "hit" - end of range)
cut-down whip - 381 feet

Half the proper length is a considerable deviation from ideal. As Larry Fisher of Lectrosonics has often said, in the best circumstances a bent and rusty coat hanger will function just fine as an antenna. But, under challenging circumstances careful attention to detail is likely to pay dividends. 

David

Great Post.  Interesting info. from the tests. Thanks.

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On 09/05/2017 at 7:17 AM, Christopher Salazar said:

An inch makes a big difference in performance. However, I've learned that girth is just as, if not more, important.

 

So you are telling me I should make my antennas thicker? ;-)

But seriously, would it be an ok idea to put a layer of shrink wrap cable over them to make them more robust and last longer? As especially TX antennas can suffer a lot of abuse over their life span.

On 09/05/2017 at 1:39 PM, Eric Toline said:

Most antennas are cut to be optimal at the center frequency of the specific block they are meant for. If a block is say 500Mhz to 550Mhz the antenna is cut for 525Mhz. The closer to the center frequency that you can tune to the better your results should be.

Interesting point to keep in mind, as it then means if I've got a block I know I won't be using half of (such as blk27) then I could slightly optimize the antenna length by cutting it to the length to match the middle of the first half of that block.

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A length of shrink tubing is a very good idea as it does not affect transmission or reception to any noticeable degree and as mentioned above it offers great protection. Do it, you won't regret it. 

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