Best "short/compromise" low band duck???

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LIScanner101

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I know that "short" and "low band" are oxymorons when it comes to antennas, but sometimes you have to do what you have to do.... :cool:

I know I'm not going to get gangbusters low band coverage with a short antenna but maybe some of you have some good field experience with the following - does anybody have any experience with either of these two antennas:

Comtelco PEXW30 (broadband, 30-90MHz)
Comtelco PEXL42

They are featured here:

Comtelco Portable Rubber Duck Antenna Information Page 1

My main coverage area would be 42MHz (CHP) when I'm traveling to CA, and 46MHz (local NY fire dispatch).

Thanks for any help!
 

br0adband

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The only respectable answer here (at least in my opinion) for VHF-Lo coverage in terms of a "duck" would still be getting a telescopic whip of whatever kind, the longer (at maximum extension) the better and at least long enough at max extension to get within 10-20 MHz of your target area as a quarter wave which would mean 66" for a 1/4 wave antenna at 42 MHz. Yeah, that's one long damned telescopic whip, I know, 5.5 feet but I've seen them, seriously. :)

Worst comes to worse: As I mentioned in another thread, look for one of those "emergency CB radio kits" that were popular years ago. They always came with either a "ducky" about a foot long that would be relatively tuned to the ~27 MHz CB range, or they had a magnetic base antenna with a telescopic whip on it (screws on when required). Find one of those and just find a much longer telescopic whip, or make one from an old VHF TV antenna of some kind.

I've owned telescopic whips years ago that would extend to 75" so they're out there, somewhere. Check thrift stores in your area, maybe you'd find something useful, and eBay has some that will extend to 50"+ that I've seen listed for sale in the past too.

There's always just a piece of flexible coax with the shielding removed too, or the classic "piece of wire" antenna which always works, more or less.
 

LIScanner101

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I know there's no such thing as a free lunch :D

I've toyed with the idea of the "long wire sticking out of a BNC" antenna but there's always an issue of how to suspend the top. Not always possible to hang it due to ceiling finish issues but I suppose it's worth a shot, or I'll just look for one of those telescopic antennas on steroids (I've seen them on ebay too).

Thanks.
 
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My choice would be an MFJ1810T, this is designed for the FT817 with a BNC base, extended it covers 10 Meters, if you collapse it the resonant point should go up in frequency, a little experimentation should yield good results for your desired coverage.
 

hertzian

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My main coverage area would be 42MHz (CHP) when I'm traveling to CA, and 46MHz (local NY fire dispatch).
A quicker option that I use for portable light-duty CHP monitoring is either one of two Radio Shack loaded telescopic whips - both of which are tuned to a center freq near 42 mhz when fully extended. It does fine at 46 mhz as well since with RS whips, we aren't dealing with a station-master inside your room. :)

The #20-006 collapses to about 8 inches with a standard bnc on the end. The slightly longer #20-551 has a right-angle bnc which makes it easy for back-of-set, however the bottom section does not collapse, so traveling length with the top collapsed is about 16 inces or so.

The problem is getting an adequate groundplane. Rather than use the random-wire ground that consists of the radio chassis and wallwart cable to the ac lines, you can try to "tune" it with an RF choke, about 5 1/2 feet away from the radio.

The RS #273-105 works ok for this since it is a 30-300mhz choke. Wrap about 5 or more turns inside the choke, and snap it shut without damaging the wall wart cable.

OR, you could place this choke right at the power-jack of the radio, and run two opposing 5 1/2 foot wires from the chassis of the radio. Slope them at 45 degrees if you like.

The RS loaded whips do very adequate service for light-duty portable low-band monitoring at 42-46 mhz when fully extended PROVIDED you put at least a tiny amount of work into improving the ground plane.

OR, perhaps look into using a bnc-magmount like the MFJ-332B, although this is not ideal especially at lowband - but as you have acknowledged, one always has to weight the pros and cons of every situation.

This is one reason why using the #20-006 with a handheld is not always the greatest - hand capacity at low band does not make for the greatest ground plane. :) Enthusiasts will want to run at least one 5 1/2 foot "rat tail" from the bnc shell.
 

prcguy

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This thread got me curious so I ran a test this morning between a few antennas. I've had a couple of tunable low band ducks for years that I tuned to 6m but have never used.

Using an AOR AR8200MKIII handheld I tuned in a local 6m repeater with an Austin Condor antenna and got one S meter bar and very noisy receive. I then tried a Thales 13" antenna from an MBITR and it was also about one bar and noisy receive.

Then the ?? brand, maybe Tuff Duck, 11" long tunable that looks like a standard VHF duck with a thin extension on top that has a tuning slug accessible under the top cap. This antenna was sharply tuned to 51MHz but the repeater was in the upper 53MHz range where the antenna was not optimized and it had three bars with reasonable signal strength.

The last antenna was a top loaded Comet MH-510 6m, 2m and 440 antenna that's 21" long. This had 5 bars and the signal was full quieting.

So, if you can find a tunable VHF lo duck you can gain slight improvement over a random broad band duck while keeping the size manageable but in the end bigger is better and bigger plus tuned to your specific freq is even better. I believe you could trim the coil on a Comet MH510 to resonate the 6M coil in the 42MHz range while keeping the 2m and 440 side intact.
prcguy
 

LIScanner101

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hertzian,

Thanks for the tips. I recall us talking about the RS whip and the addition of the common mode RS chokes several feet from the feedpoint. I got myself 5 of those chokes but unfortunately the whole setup was a little disappointing overall. However, now that I own an NMO to N connector mounted on a right angle bracket I might experiment :) This NMO has provisions for (4) 20" steel radials but I am going to temporarily try (4) 66" pieces of wire for nice long low-band groundplanes. I can coil the whole mess up and toss it in my suitcase. For the actual antenna I'll try a telescopic antenna if I can find one that's 5 feet long or a little longer (saw something recently on the web).


prcguy,

Thanks to you too! About that Comet/Maldol - how does one tune the coil? I might give that one a shot. Also what frequency did you test it out on?
 

RadioDaze

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Thanks. What was your low band "target" frequency with that PEXL36?
Typical CHP between about 39.2 and 45.7.

From coastal Orange County, in a condo, on the wrong side of the building, I've heard Arrowhead division... probably 65 miles line-of-sight. In the vehicle, I use this window mount for it ( Duckie Window Mount with BNC ) and seem to average from 10 to 30 miles depending on terrain. I wish it was waterproof, but some occasional light precip hasn't seemed to hurt it any.
 

LIScanner101

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RadioDaze,

I've seen those before. I don't like the fact that they use such skinny coax but for low band and with only 6' of it I doubt it would attenuate much. Thanks for the tip.
 

RadioDaze

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I really, really want to drill the roof, but my headliner is problematic. I managed with my last vehicle, but this one's a bear, even though it's just a few years newer model of the same thing. I literally had a dream a few nights ago in which I had the back portion of my headliner dropped, and the inner roof all nice and exposed, and I was getting ready to have at least one NMO installed. It was weird to be in such a state of bliss over such a ridiculous thing. Sadly, I woke up way too soon.
 

prcguy

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The MH-510 coild comes off the whip with an allen screw and the coil is covered with heat shrink. I believe you can cut away the heatshrink and remove turns to tune the low band resonant freq with an antenna analyzer. You can also trim the whip to favor the 150MHz public service band.
prcguy

hertzian,

Thanks for the tips. I recall us talking about the RS whip and the addition of the common mode RS chokes several feet from the feedpoint. I got myself 5 of those chokes but unfortunately the whole setup was a little disappointing overall. However, now that I own an NMO to N connector mounted on a right angle bracket I might experiment :) This NMO has provisions for (4) 20" steel radials but I am going to temporarily try (4) 66" pieces of wire for nice long low-band groundplanes. I can coil the whole mess up and toss it in my suitcase. For the actual antenna I'll try a telescopic antenna if I can find one that's 5 feet long or a little longer (saw something recently on the web).


prcguy,

Thanks to you too! About that Comet/Maldol - how does one tune the coil? I might give that one a shot. Also what frequency did you test it out on?
 
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