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How important is antenna length?


Mark O'Russa
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After running across checked my Zaxcom antennae and found them to be a little off of the correct length for my block. So I want to ask, how important is antenna length?

 

I have two QRX receivers and some TRX transmitters. They have all operated well-enough. During my measurements I found some to be 1/4" too long, which puts them 2 blocks away according to the Zaxcom antenna length chart. The current TRX and QRX manuals show the same chart. I used precise digital calipers for the measurement.

 

I can't say I noticed any difference now compared to before. There are so many variables that affect reception, how do I know if the antenna length was a weak point?

 

I'd like to hear from Glenn and Larry.

 

Mark O.

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As a point of reference, I have 2 sets of Sony WRR 27 wireless in the 950mhz band. The tx antennas are about 2.75" long, I don't have any antennas for the rx which uses a BNC connector so I tried a 12" long BNC terminated VHF antenna that was made for the 170MHz band for a Lectro 185 set. Lo & behold it worked just fine out to about 100ft line of sight. Draw your own conclusions.

 

Eric

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As a point of reference, I have 2 sets of Sony WRR 27 wireless in the 950mhz band. The tx antennas are about 2.75" long, I don't have any antennas for the rx which uses a BNC connector so I tried a 12" long BNC terminated VHF antenna that was made for the 170MHz band for a Lectro 185 set. Lo & behold it worked just fine out to about 100ft line of sight. Draw your own conclusions.

 

Eric

100' line of sight isn't enough to draw a conclusion, except maybe about the fallacy of the correlation between transmitted output power and range. But while the antenna length is certainly a factor that must be considered, a small variance will almost always go unnoticed in real-world performance, as original poster's experience suggests.

 

Glen Trew

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What about those transmitters with 230 Mhz bandwidth?

Wisycom MTP40

http://www.wisycom.com/www3/products/product/mtp40#1

 

Wisycom seems to reckon about 100Mhz per antenna

Whip Antenna UHF for MTP40/MTP41
Code 507: band 1 range 470 ÷ 547 MHz
Code 590: band 1 range 547 ÷ 640 MHz
Code 616: band 2 range 566 ÷ 672 MHz
Code 732: band 2 range 672 ÷ 798 MHz
Code 552: band 3 range 510 ÷ 595 MHz
Code 646: band 3 range 595 ÷ 698 MHz

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" I'd like to hear from Glenn and Larry. "

they are both easy to contact directly....

but of course, you are looking for discussion...

 

I remind everyone that radio antenna design is very technical, and has been a major topic for radio (the big RADIO, which includes all RF transmissions) folks for decades, and still continues today.

I remind also of some reading available on the Internet, and in books, including those from the ARRL...(for example: http://www.arrl.org/shop/ARRL-Antenna-Book-22nd-Edition/

 

returning to the basic, and rather inefficient whip antenna attached to a TX or RX, as a practical matter slight variations in length are far less important than the existence of a counterpoise (ground plane), the proximity to other objects, particularly metal objects --and this includes antennae on other nearby units--, and blockages to line of sight. 

As a more technical matter, the antenna must be tuned to the circuitry it is connected to and any detuning affects the performance of the equipment (for example current consumption), so of course it is important to connect proper a antenna, especially to a transmitter.

" if the antenna length was a weak point? "

it wasn't.

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