Attach directly to radio?

[KC3AOL]

Being a new ham, I don't have a lot of experience and I was wondering if attaching an antenna directly to a mobile radio (no coax) would work or is the coax needed to get a good SWR? For example, take a Kenwood TM-V71A and attach a Comet CA-2X4SR. I was just thinking a setup like that might be good as a backpack rig or a good portable system.

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[WA4STO]

There are a couple of reasons why you'd want to use coax and why you wouldn't.

But first, CAN you attach the antenna directly?  Sure, provided that the radio has a UHF connector on it.  Otherwise, you'd need to use an adapter which would introduce some loss. 

I'm certainly not an expert on these two items, but I would guess that it would be durned near impossible to just plug the antenna into the radio, unless you had a four foot (however long the antenna is) clearance between the radio and the nearest wall.

Overall, I think you'd be well advised to always use some coax in the mix.  Why?  Because of the huge possibility of straining the connector.  Without the coax, one decent BUMP! could ruin your day.  Coax adds flexibility.

Nice radio!

73

Luck, WA4STO
http://www.qrz.com/db/wa4sto

[gil]

Hello,

Most mobile antennas expect to see a counterpoise of some kind, which of course ends up being the car chassis in many cases. So, if you plug in a mobile antenna directly into the radio via an adapter, you will most likely need to connect a wire to the radio chassis and let it dangle down. I would start with a quarter wave wire, and experiment with length for best SWR.

Gil.

[KC9TNH]

From undisclosed location in hostile in-law country...

The antenna you mention has a PL-259 (male HF) connector according to its literature. It would be advisable, simply in the interest of being nice to the radio, to put something like a short piece of coax between them so that youre big broadband whip isn't stressing the connector interface on the radio.  That's just one reason.

Your idea of a packable "package" is a good start in terms of bulk (if you must have all bands the radio is capable of) but, wait....  did you also want to power that TM-V71 at its full power output?  Now you start to add non-hump-friendly battery power.

Welcome to the forum.
:)

Back to the fray; people really should secure their internet capabilities you know...
8)

[gil]

And I would suggest not operating with that antenna too close to your head...

Gil.

[KC9TNH]

And I would suggest not operating with that antenna too close to your head...

Gil.

(back in the Badger country now, thankfully)
Gil mentions the other reason big-time & man-portable whips or other close proximity radiators at high frequencies can bite you, even at much lower power.

Several websites available to do the same thing, but amounts to an RF safety assessment.
Try this one and do an apples to apples comparison of 50w at both 7mHz and 440mHz, 3dBi gain for both, proximity 1 foot.

http://www.wirelessconnections.net/calcs/rfsafety.asp

[KK0G]

While the RF exposure at VHF/UHF with an antenna from a 50 watt transmitter that close to ones body is a serious issue, the duty cycle is likely to be very low because drawing that much current is going to run any man portable sized battery dead in very short order making it sort of a moot point. In other words it's not a very feasible setup to begin with.

[KC3AOL]

Hello,

Most mobile antennas expect to see a counterpoise of some kind, which of course ends up being the car chassis in many cases. So, if you plug in a mobile antenna directly into the radio via an adapter, you will most likely need to connect a wire to the radio chassis and let it dangle down. I would start with a quarter wave wire, and experiment with length for best SWR.

Gil.

Good point about the counterpoise. I actually added a counterpoise "rat tail" to my HT and that has helped it out a lot.

BTW, while thinking about this, I had another idea. How about using an umbrella as a base plane? Anybody seen anything like that tried?

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[KC3AOL]

Your idea of a packable "package" is a good start in terms of bulk (if you must have all bands the radio is capable of) but, wait....  did you also want to power that TM-V71 at its full power output?  Now you start to add non-hump-friendly battery power.

Yeah, didn't think about the power for a 50W transmitter. Now that I have a better understanding of the range on a 5W HT (which it's actually pretty good), I think an HT is just fine and will run a lot longer on the internal battery. I'm actually looking at picking up a few Puxing PX-UV973 HT radios. They get really good reviews and have a cross band repeater capability. I'm thinking that I might be able to put together a rig with one of them in a waterproof box, a slim Jim antenna, and a solar panel. Throw it up in a tree and have a low profile local repeater system.

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[KC3AOL]

And I would suggest not operating with that antenna too close to your head...

Gil.

I did consider that, but hasn't gotten around to looking into what the exposure would be.

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[KC3AOL]

Anyway, thanks everyone for the feedback.

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[RichardSinFWTX]

I've got a Yeasu FT-8900R fully backpack portable with a 10aH battery, a buddipole antenna, YoYo-Tenna, and Opek HVT-400B (what can I say, I like having options in my antennae) along with 250' of 550 cord.  The whole thing weighs in at just under 30# and can be operated on the move. 

[KC3AOL]

I looked around a little and found someone who had a similar idea on the umbrella antenna:
http://www.digitalcartography.com/n0eq/umbrella.htm

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[RichardSinFWTX]

That's pretty slick!

[gil]

How about using an umbrella as a base plane? Anybody seen anything like that tried?

The best idea I've heard in a long time!

Gil.