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Author Topic: BNC 1/4 wave 2m QRO whip  (Read 335 times)
KE8FWJ
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Posts: 34




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« on: December 03, 2018, 10:14:16 AM »

Have a 80Watt 2m FM radio that I wish to use on the odd occasion in the car.

Looking to use a MFJ-310 window mount clip with counterpoise radials attached.

https://www.mfjenterprises.com/Product.php?productid=MFJ-310
 
Cannot seem to locate any BNC 1/4 lambda whip for 2m that may handle any inadvertent 80Watt FM transmissions. Any suggestions where I can buy one?

I don't mind replacing the supplied coax and BNC socket if necessary.

Thanks in advance Smiley

Victor
« Last Edit: December 03, 2018, 10:16:23 AM by KE8FWJ » Logged
K5LXP
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« Reply #1 on: December 04, 2018, 04:13:36 AM »

Cannot seem to locate any BNC 1/4 lambda whip for 2m that may handle any inadvertent 80Watt FM transmissions.

Based on what criteria?  There is nothing about a quarter wave that is particularly power sensitive.  Because it's closely matched it would be my guess that the only real power limit is that of the coax.  A BNC is good for a few hundred watts at VHF.  Even "skinny" coax like RG-316 can handle 80W, no problem at all for RG-58.

Mark K5LXP
Albuquerque, NM
 
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KE8FWJ
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« Reply #2 on: December 05, 2018, 08:45:30 PM »

The 2m whips available in the shops are not rated more than 20Watts. I'm looking for similar BNC whips to mount on a MFJ-310 but with higher power ratings.
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K5LXP
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« Reply #3 on: December 06, 2018, 04:27:22 PM »


I understand the issue now, it's not very easy to find a basic quarter wave whip terminated in a BNC.  Seems like most everything out there with a BNC is an HT antenna which are shorter, and have a loading or matching network that will limit power handling.  I have a BNC whip antenna that I use on my radio bench that I made years ago by grinding down a stainless whip to the diameter of a center pin, then bonding it inside a BNC connector with epoxy.  Probably a few different ways to make one but a cursory search didn't find any ready sources for purchase.  Seems like such a simple problem but I guess not many folks use BNC mounts as mobile antennas.

Mark K5LXP
Albuquerque, NM
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WB6BYU
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« Reply #4 on: December 07, 2018, 07:17:52 PM »

I have a couple such whips with BNC connectors, but have no idea where
they came from or the power rating.  (But there isn't anything obvious
that would limit the power.)

One is a piece of stranded wire inside a piece of plastic tubing.  Think someone
was building them in their garage about 15 years ago.   Might need
stiffer tubing to stand up at highway speed. A BNC plug designed for RG-8X
should take a larger wire size than those for RG-58 (or especially RG-59).

In general, flexibility may be your biggest problem: 1/4 wave whips designed
for HTs are often too flexible (for safety on an HT) to hold up at freeway speeds.

The other is a commercial steel whip in a BNC with the connector filled with
epoxy.  It is also pretty flexible.  Something like 1/16" brass brazing rod should
work: see what size seems stiff enough.  You might need to solder the center
pin straight onto the end, or use a short wire to make the connection, then
fill the back end of the plug with epoxy or hot melt glue to give it sufficient
mechanical strength.

I also have a few telescoping whips on BNC plugs, but I wouldn't trust those
for mobile use.
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K5LXP
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« Reply #5 on: December 07, 2018, 09:01:55 PM »


Larsen makes a PL-259 whip, the PQ to use with SO-239 mounts.  They make BNC mounts so you'd think there'd be companion antennas to go with that.  Availability notwithstanding, I wonder if the MFJ mount would be up to the stresses of a VHF quarter wave at speed on a car. 

Mark K5LXP
Albuquerque, NM
 
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KE8FWJ
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Posts: 34




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« Reply #6 on: December 08, 2018, 02:23:38 PM »

I have a couple such whips with BNC connectors, but have no idea where
they came from or the power rating.  (But there isn't anything obvious
that would limit the power.)

One is a piece of stranded wire inside a piece of plastic tubing.  Think someone
was building them in their garage about 15 years ago.   Might need
stiffer tubing to stand up at highway speed. A BNC plug designed for RG-8X
should take a larger wire size than those for RG-58 (or especially RG-59).

In general, flexibility may be your biggest problem: 1/4 wave whips designed
for HTs are often too flexible (for safety on an HT) to hold up at freeway speeds.

The other is a commercial steel whip in a BNC with the connector filled with
epoxy.  It is also pretty flexible.  Something like 1/16" brass brazing rod should
work: see what size seems stiff enough.  You might need to solder the center
pin straight onto the end, or use a short wire to make the connection, then
fill the back end of the plug with epoxy or hot melt glue to give it sufficient
mechanical strength.

I also have a few telescoping whips on BNC plugs, but I wouldn't trust those
for mobile use.

Making a 1/4 lambda 2m with a BNC is indeed very easy as you've described. Simply solder the center pin to the radiator.  Using it on a car,in the wind at 70Mph, may prove interesting. Not sure what the power rating would be, but would certainly exceed my power requirements.


Larsen makes a PL-259 whip, the PQ to use with SO-239 mounts.  They make BNC mounts so you'd think there'd be companion antennas to go with that.  Availability notwithstanding, I wonder if the MFJ mount would be up to the stresses of a VHF quarter wave at speed on a car. 
 

Yes, know about the Larsen antennas. Also not easy to determine which are 19" or helicals. If the MFJ mount displays any indications it will throw the antenna then will cross that bridge when the time comes. Other option may also be to use a flag carrier that slips over the window as well, although would prefer to remedy the MFJ as much as needed.
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WB6BYU
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« Reply #7 on: December 09, 2018, 09:55:21 AM »

If you can get a whip with a PL-259 plug, consider using it with an adaptor.
I have a 5/8 wave whip that I use that way on a BNC connector.

In practice, building your own whip with a BNC plug is not always as simple
as it might seem, because the whole in the center pin often isn't large enough
for the desired whip diameter.  The best method would be to turn down the bottom
of the whip on a lathe to become the center pin of the connector, but that is far
beyond the capabilities of my workshop.  Hence the need to get more creative
with jumper wires, glue, shins, heatshrink tubing, etc.

In some cases I've used "twist-on" connectors (because I have a bunch in my
junkbox) with some sort sleeve on the element to engage the threads that normally
connect to the shield. This can make a sturdy antennas but the center pin contact
isn't always reliable unless you can use the right size wire.  It's much easier to
solder to the center pin of a PL-259.

I think one of the better approaches would be to use some sort of stiff tubing
or even fiberglass tube that fits inside the base of the plug for mechanical
support and provides the physical support for a wire that fits the center pin.
You might check kite stores or plastic suppliers, though I've also picked up
hollow fiberglass tent poles that would work.


Another thing to remember is that the power rating on most rubber ducks will be
due to overheating, that is, heat build-up over time due to poor efficiency.  They
probably will survive the momentary application of higher power.  Just set your
power to minimum (usually 5 or 10 watts for a mobile rig) and they should
be fine:  if they overheat in normal use then you want something more
efficient anyway.
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KE8FWJ
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Posts: 34




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« Reply #8 on: Yesterday at 03:17:33 PM »

Ended up with a Larsen 1/4 lambda with BNC connector and an OPEK clip on window mount.

 Smiley Smiley Smiley

Time to APRS QRO

 Cool Cool Cool
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K5LXP
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« Reply #9 on: Yesterday at 04:07:25 PM »


What part/model number is the antenna?  I only saw the PL-259 and stud mount whips in their mobile catalog.

Mark K5LXP
Albuquerque, NM
 
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KE8FWJ
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Posts: 34




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« Reply #10 on: Today at 08:17:42 AM »

Larsen BNCQ
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