Railfan Technology > Telescoping Antenna

I have a telescoping antenna for a hand held scanner, and I need some advice on how to set it up.  It's 26" long with a coil 9" above the bottom.  What is the best length for this, and how should the bottom vs the top telescoping be set?

Thanks,
Neil

Is this for the RR band exclusively or for a wider band of some sort?

Any manufacturer or model number info?

Does it look kinda like this:

https://www.thunderpole.co.uk/handheld-scanner-antennas/retractable-telescopic-bnc-antenna-centre-loaded.html



Edited 1 time(s). Last edit at 10/18/22 12:19 by TCnR.

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TCnR Wrote:
-------------------------------------------------------
> Is this for the RR band exclusively or for a wider
> band of some sort?
>
> Any manufacturer or model number info?
>
> Does it look kinda like this:
>
> https://www.thunderpole.co.uk/handheld-scanner-ant
> ennas/retractable-telescopic-bnc-antenna-centre-lo
> aded.html

========================

That's exactly what it looks like.  I'm interested in the rail frequencies only.
 

Straight answer is 18 inches with the center of the load in the middle. There's probably an insulator at the base of the antenna, measure from there or basically the top of the BNC connector, theory says to measure to the top of the widget on the tip.. Trim as required for best reception.

Take the highest frequency you expect to use and plug it into this formula then divide by 1/4, 1/2 or 5/8, 1/4 being the standard and the other two have some antenna gain or larger antenna pattern.

https://www.everythingrf.com/rf-calculators/frequency-to-wavelength

Change to inches and then divide, or divide and then change to inches.

Everybody has their favorite frequency to use but with an extendable antenna there's plenty of room for slop.

Try using the local NWS 24 hour broadcast to check out the antenna and try to optimize the length.

Should add that the center load doens't really do anything for this application, it would be better to find one without it, for safety, stability, less to break, etc. The 1/4 wave antenna is often the best choice to reduce any intermodulation questions... those pager noises.


 



Edited 1 time(s). Last edit at 10/18/22 15:12 by TCnR.

TCnR Wrote:
-------------------------------------------------------
> Straight answer is 18 inches with the center of
> the load in the middle. There's probably an
> insulator at the base of the antenna, measure from
> there or basically the top of the BNC connector,
> theory says to measure to the top of the widget on
> the tip.. Trim as required for best reception.
>
> Take the highest frequency you expect to use and
> plug it into this formula then divide by 1/4, 1/2
> or 5/8, 1/4 being the standard and the other two
> have some antenna gain or larger antenna pattern.
>
> https://www.everythingrf.com/rf-calculators/freque
> ncy-to-wavelength
>
> Change to inches and then divide, or divide and
> then change to inches.
>
> Everybody has their favorite frequency to use but
> with an extendable antenna there's plenty of room
> for slop.
>
> Try using the local NWS 24 hour broadcast to check
> out the antenna and try to optimize the length.
>
> Should add that the center load doens't really do
> anything for this application, it would be better
> to find one without it, for safety, stability,
> less to break, etc. The 1/4 wave antenna is often
> the best choice to reduce any intermodulation
> questions... those pager noises.
>
>=======================

Thanks!
>  

Personally, I would throw the thing in the trash and buy a gain-type flexible "rubber ducky" antenna--the Diamond RG77CA, for example.  Here is why.  If you are using telescoping antenna on a portable radio (scanner, etc.), the antenna connection is often the weakest mechanical part of the radio.  Because the telescoping antenna has relatively little flexibility, when you put any bending stress on the antenna, that physical force is nearly all concentrated on the antenna connector on the radio.  That kind of force does not take much to break the electrical connections between the antenna connector and radio circuitry.  At that point, you have no antenna at all, and the radio may not even be repairable.  I've seen plenty of portable scanners over the years that have died an premature and avoidable death this way.  A telescoping antenna is best used on something like a desktop scanner that doesn't move around much.

https://www.amazon.com/Diamond-Original-RH77CA-Dual-Band-Handheld/dp/B00M1X73EA

Telescoping antennas are from the day of desktop scanners, adjust the antenna to your band of interest, place the desktop near a window and things would work pretty well. No cables, no worries and most folks were just happy to hear something.