146 / 440 Mhz colinear base antenna - Opinions

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mtindor

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I've been playing around with radios and scanners since the late 70s/early 80s. I've owned quite a few commercial amateur antennas (yagis, omnis, single and dual band) and have concocted a number of HF/VHF/UHF/900 Mhz antennas as experiments. During all of the time of having a 146 / 440 antenna, I never really had the opportunity or urge to compare them on receive to an omni scanner antenna designed for VHF / UHF operation.

From the perspective of a scanner listener (usually only relying upon an antenna for receive and not transmit), a lot of things change.

Advertised "gain" doesn't mean a whole lot if you are looking at a transmit antenna to use for receive-only

Why? Gain figures on antennas are usually transmit gain figures. It is entirely possible to have an antenna with some gain that doesn't have the required capture area to effectively achieve a significant increase in receive signal strength.

With the above said, and taking into consideration the old adage about opinions being akin to a-holes, I'm going to ask a question....

I've been thinking about purchasing a Diamond X200A dual-band antenna (146 / 440 Mhz). This is a colinear vertical. It's a nearly 8.5 foot tall antenna. If this antenna were "tuned" for 152 / 455 it would be "better", but it's not "tuned" for 152 / 455 and I wouldn' want it to be.

My question, for those with some antenna theory under their belt, is whether this antenna is going to be a good _receive_ antenna on 150-170 / 470 without any retuning. Since I don't currently intend on using it as a transmit antenna, I don't really have to worry about SWR/resonance from that perspective. But is a 146 / 440 Mhz antenna signficantly "detuned" on recieve for it to be perform well at 150-162 and 450-470?

Bottom line is that I want a single, quality, omnidirectional antenna of reasonable length and covering VHF and UHF that I can have up for a decade and never have to touch. I want it to perform better as as a recieve-only antenna than any well-known omnidirectional scanner antenna on the market, knowing that one day I might actually give a damn about 2m / 440 (being an amateur radio op) to actually hook a transceiver up to it.

So for those with an something more than opinion [such as some real world experience, technical knowledge], am I going to be amazed at the increased receive gain if I buy this antenna to replace my ST-2 and various other "scanner hobby" antennas that I"m currently using for VHF / UHF?

Your opinion?

Mike
 

prcguy

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Antennas are completely reciprocal, whatever the gain figure is on transmit it will be the same for receive.

If you have been using a Discone with roughly 0 to 2dBi gain, then switch to an antenna rated for say 6dBi gain and its at the same height you will notice a definite improvement. Problem is many antennas, especially amateur and scanner types have made up gain figures.

In my experience, most amateur 2m/440 antennas drop off noticeably when you get into the mid 150s or above the 460s. It may work better than the scanner antenna it replaced but won't be as impressive on commercial freqs as it might be on amateur freqs.

I have not specifically used the Diamond X200 but have a similar height 6m/2m/440 version from Comet at my office that works a little better on commercial than the Discone sitting next to it. I also have the giant 17ft Comet GP9CN dual band commercial antenna and it hears ok on 2m but the VSWR is about 10:1 and I cant transmit there. The UHF side is not as bad but you can tell its down some at 440MHz. This antenna is factory tuned at 155 and about 465MHz.

Comet may offer shorter dual band versions similar to the X200 cut for commercial freqs like they do with the GP9N and GP9CN series if you don't need to transmit in the amateur bands. Or buy my abused GP9NC for $75, pickup only.
prcguy
 

kc2rgw

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Any of the big Diamond or Comet models are well made.

Biggest tip is to weather seal the joints. Tape them up really well. If you really want to be fanatical, put wax on it before it goes up. Time in the sun rots the fiberglass and vibration from the wind loosens the joints. The downfall is when they get waterlogged. Even then, you can generally pull them down, re-seat the joints and seal them again and they are fine.
 

zz0468

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VHF/UHF? Up for a decade? Might transmit on it later?

I'd use a Kreco discone, with something like one of these installed inside at the end of the feedline:

http://www.minicircuits.com/pdfs/ZX60-33LN+.pdf

It's that decade thing that cinches it for me. Kreco antennas are built like a tank. An antenna specifically tuned for the amateur bands is going to have unpredictable performance outside that band. The gain specification will be invalid, and the pattern specification will be invalid. I get quite good results with a quality unity gain antenna, low loss coax, and if I really need it (I rarely do), I can put a preamp on-line.
 
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