SWR

[Guest jamesmaninpantyhose@yahoo.]

How much length do I have to trim from my GMRS Magnet mount antenna to get a proper SWR on 462mhz James Black WQZF786

[BoxCar]

The SWR curve is bell shaped. As you go up or down from the resonant frequency the SWR will increase so your question can't be answered until we know if the resonant frequency is higher or lower than your target frequency.

[marcspaz]

Along with what is mentioned above, you should be tuning for 465.1375 MHz, the center of all of the channels.  That will allow for maximum performance on all channels/frequencies.

[WyoJoe]

7 hours ago, Guest jamesmaninpantyhose@yahoo. said:

How much length do I have to trim from my GMRS Magnet mount antenna to get a proper SWR on 462mhz James Black WQZF786

If you have a GMRS magnet mount antenna, it may already be properly tuned so you don't have to trim anything. Most GMRS antennas are tuned to about 465 MHz, because this is the center of the GMRS band when you factor in the frequency range from 462.xxx to 467.xxx.

If your antenna is already tuned to 465 MHz, then you'll have to figure out how to extend it to tune it perfectly for 462 MHz, because when you go down in frequency, you increase the signal wavelength, and thus, need a longer antenna, as the antenna length is a ratio of the wavelength.

The best bet would be to get an antenna analyzer and see what your antenna is tuned for. If you have, or know anyone with, a NanoVNA, it will work well for this purpose. Otherwise, if you know anyone that is a "ham" (amateur radio operator), they may have what you need to analyze the antenna.

[WyoJoe]

One other thing I neglected to mention in my post above, if the antenna is tuned to 465 MHz, it should perform very well on 462 MHz, and should not need to be retuned.

There is more to antenna performance than just a great SWR, as I'm sure many on this forum will tell you if you ask.

Have you checked the antenna's SWR? Is it below 1:2?

People generally want a "perfect" 1:1 SWR, when in reality, an SWR below 1:2, or even higher in some cases, is acceptable.

[marcspaz]

1 hour ago, WyoJoe said:

One other thing I neglected to mention in my post above, if the antenna is tuned to 465 MHz, it should perform very well on 462 MHz, and should not need to be retuned.

There is more to antenna performance than just a great SWR, as I'm sure many on this forum will tell you if you ask.

Have you checked the antenna's SWR? Is it below 1:2?

People generally want a "perfect" 1:1 SWR, when in reality, an SWR below 1:2, or even higher in some cases, is acceptable.

 

Good points... Chasing great SWR is not needed in many cases.  There is an aphorism I like... "The best is the enemy of the good."  or the modern version "Perfect is the enemy of good."

 

It is widely accepted that an SWR of 3:1 is the maximum safe SWR.  Many radio's will alert or shutdown transmit at anything above 3:1; and still others will detune (pull back power) if the SWR is otherwise unsafe.

 

At 3:1, if you start with 50w into the antenna, you will have 37.5w ERP (on a zero gain antenna).  Not fantastic, but I wouldn't be tossing stuff in the trash either.  A 2:1 will be about 44w ERP, which is pretty good.  Depending on how performance is elsewhere, I may not even attempt to improve a 2:1 in a low power system.  Especially when many antenna manufactures don't even guarantee better than 2:1 on their budget-friendly products.