Scanner Antennas

[Citizen]

I see antennas advertised as “scanner” antennas.  Does this mean that scanner antennas can only be used for RX only, or can any antenna be used for both RX and TX?

Why do I ask?  I bought an antenna specifically for my old RS VHF/UHF scanner.  Obviously the scanner is multi band, so I’m assuming the antenna is too.  I can receive some bands ok, like 70cm ham (like 444 and 453 Mhz), and 2m ham (like 146 Mhz), and business radio (like 464 Mhz).  I even get Marine band ok (156 Mhz).  But for some reason other frequencies in the middle of those are horrible, like GMRS (462) and FRS (467).

 

I’m hoping someone with some antenna expertise can answer these question:

1. Can I use a scanner antenna for TX on what-ever band?

2. Why is a multi-band scanner antenna good for 464 Mhz, but lousy for 462 and 467

Thanks in advance.

...

[BoxCar]

The other thing to consider is that an antenna designed for receiving may not handle the transmitter's output power.

[Citizen]

boxcar and mbrun, thanks much for those very clear and understandable answers.  Michael, I have a better understanding now about my scanner antenna and why it is good for some, but not all frequencies, and boxcar, I don't think I'll be using it for TX on any radio. 

Thanks again!  Love myGRMS and how people on here are willing to share knowledge!

: )

[mbrun]

I see antennas advertised as “scanner” antennas.  Does this mean that scanner antennas can only be used for RX only, or can any antenna be used for both RX and TX?

Why do I ask?  I bought an antenna specifically for my old RS VHF/UHF scanner.  Obviously the scanner is multi band, so I’m assuming the antenna is too.  I can receive some bands ok, like 70cm ham (like 444 and 453 Mhz), and 2m ham (like 146 Mhz), and business radio (like 464 Mhz).  I even get Marine band ok (156 Mhz).  But for some reason other frequencies in the middle of those are horrible, like GMRS (462) and FRS (467).


 
I’m hoping someone with some antenna expertise can answer these question:

1. Can I use a scanner antenna for TX on what-ever band?
   
2. Why is a multi-band scanner antenna good for 464 Mhz, but lousy for 462 and 467
   

Thanks in advance.


...

A scanner antenna can be thought of as a jack-of-all-trades, master-of-none antenna. This means the antenna, by design, prioritizes utility on many frequencies over optimum performance on any frequency. Since a scanner may have only one antenna input yet it can scan a wide range of frequencies, the ideal scanner antenna can be thought of as one which provides equal performance over a wide frequency range.

Yes, a scanner antenna can be used for transmit, just as any piece of wire can be used for transmit. How well it works, and how long you radio will last using it is purely a function of the antenna’s electrical and radiation characteristics on the frequency in question. If the SWR it presents to the transmitter is within acceptable range for the transmitter, you are good to go.

The simplest and most foundational of all antennas is the dipole antenna. Such an antenna resonates quite optimally at one frequency and thus performs exceptionally on it. Near that frequency it does OK to, but its performance degrades commensurate with the difference in frequency from its resonant value. The range of frequencies in which the antenna presents a certain range electrical characteristics to the radio that is deemed acceptable is referred to as its bandwidth. For example, my commercial GMRS antenna as a bandwidth of 10MHz and it only performs well in that range.

If you measure the performance of any antenna over a wide range of frequencies you will see an electrical pattern that mimics a mountain range. The wider the range measured the more mountains (variation) you will see. And each design variation will exhibit different patterns of peaks and valleys.

Designing antennas to work over a wide range is a major exercise in compromise. Sacrifice this to get that. That will include cases where some frequencies, even ones near one another perform quite differently, most notably in specialized antennas. A scanner antenna is a specialty antenna.

Hope this helps.


Michael
WRHS965
KE8PLM