Seeking a better "travel" antenna...

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LIScanner101

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I have a thread in the California forum about using an OCFD in hotel rooms, but I wanted to post something here so it was more antenna-related and not so much California-related:

Below is a photo of my wire OCFD I used this week while in the LA area and the Bay Area. It worked very well for me on all bands except low band CHP (42MHz range) but that was to be expected. It is MUCH more "travel-friendly" than my Antenna Specialists MON-52 that I cut in half (and reassemble) in the hotel room. However, I have a couple of questions:

1. I have been told that it doesn’t matter “much” which way an OCFD is hung (long end up or down) but I would imagine it would matter “some”. Would I have seen any difference in receiving certain bands if I hung this antenna with the long side up?

2. Are longer antennas better for indoor scanning? I came across the Comet BNC-W100RX and wonder if this would be better, especially for 42MHz??? It doesn’t seem to have any traps or coils, just a straight long antenna. What caught my eye was a) it’s only 8” when collapsed and b) it’s almost 4 feet long when extended! I am sure this would enhance low band, but would this also work well for UHF and VHF high if it was extended all the way to its max length of 44”???




 

br0adband

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Is that a regular OCFD or the "original" concept one with 66"/22" (88" total) sides - the regular OCFD is only 48"/18" (66" total) which is 5.5' and that one pictured sure looks to be quite a bit longer than 5.5' long - that is unless you're were staying at a hotel that catered to people of less physical stature like Hobbits or something. :)

Should have been able to "mount" a proper OCFD directly to the glass panel on the door without any of that excess at all. I keep looking over at my wire OCFD here beside me and then my front door and I can visually see it'll fit with room to spare, considerable room.

Anyway...

1) When properly contructed, the OCFD works as a single antenna for the most part, so no it doesn't matter if the long lobe is on top or bottom, or vice versa for the short lobe - the antenna acts as a complete resonator in either direction and works the same. I've done the "flip" operation myself on my wire OCFD the past few days and signals are the same regardless. Pretty sure this has been discussed in many OCFD-related threads over the years.

2) I wouldn't specifically say a longer antenna will be better for indoor scanning overall meaning just having one random length long antenna being used for everything and expecting everything to be better - things just don't work that way, unfortunately. Yes we're all aware that you can get better performance than any old rubber duckie cheap scanner antenna "with a piece of wire or coat hanger" but what that really means is "a piece of wire or coat hanger matched to the proper antenna length in 1/4 or 1/2 wave lengths" actually.

The issue with VHF-Lo frequencies is they are low (duh) and therefore the wavelengths are very long by comparison to VHF-Hi and UHF frequencies. If you want something that'll work great for VHF-Lo operation in the 30-50 MHz range you're going to need to either: a) make something like a dipole you can unravel as required tuned to that range (around 40 MHz centered), or b) find a telescopic whip or some kind that can extend to the 1/4 wavelength of roughly 74 inches (6 feet 2 inches). Now they're out there, actually, but tough to locate and sorta-kinda expensive.

Another solution that will improve things in that range (30-50 MHz) would be a coil-loaded CB antenna - yes, yes, I know I know you're not trying to listen to CB frequencies around 27-28 MHz, the point being those types of antennas, while being designed to work better at them, also work well for frequencies not too far off.

I remember years ago I had a Watson 1000 mobile mount CB antenna with the typical white base (they make 'em in black nowadays) and the long steel whip that was 62" long - not perfect but far better than any old rubber duckie or even a center loaded would do. I was living in southeastern VA at the time, right off Va Beach and was on a job one day and on a break I went back to my car, turned on my trusty old Radio Shack Pro-34 (this was a long long time ago, mind you) and I was picking up activity from Ft Hood way down southwest of me meaning it's located in TEXAS by about 1800 miles on 30.450 MHz as their range control was calling out warnings and info to the training groups that morning. Talk about skip, geez. ;)

And it was very clear and very readable for my entire break period, but by the time I came back a few hours later for lunch the signal had dissipated like always.

Regardless, if you're looking to get some VHF-Lo specific listening in, it wouldn't hurt to try and find a CB antenna of some kind, either a straight whip model of appropriate length (5 feet at least, gunning for that 73.8" half-wave length if you can manage it) or one of the shorter center-loaded versions used with "emergency CB radios" you can find these days. They are typically just a makeshift mag-mount plastic covered base with a telescopic whip attached like shown in the image below.



It's not the greatest thing in the world, no, and you can probably find one at a thrift store or pawn shop pretty cheap, but that antenna - with the proper adapters so you match it to your current hardware, or just replace the cabling with something better (might be a good idea considering the age of those emergency CB things, they were popular like 20 years ago) and voila, you'll have an antenna that will offer you vastly superior VHF-Lo sensitivity because it's designed to work "down under" so to speak.
 
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prcguy

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LIScanner101

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Is that a regular OCFD or the "original" concept one with 66"/22" (88" total) sides - the regular OCFD is only 48"/18" (66" total) which is 5.5' and that one pictured sure looks to be quite a bit longer than 5.5' long - that is unless you're were staying at a hotel that catered to people of less physical stature like Hobbits or something. :)

Should have been able to "mount" a proper OCFD directly to the glass panel on the door without any of that excess at all. I keep looking over at my wire OCFD here beside me and then my front door and I can visually see it'll fit with room to spare, considerable room.
br0adband,

You know, you would think I would have noticed that too....but I didn't :lol:

I'm pretty darned sure I cut the short piece at 18". However, when I cut the second piece, I "may" have cut it long enough to make the short AND long legs, meaning it's really about 5-1/2 ' long instead of 4'! Well, I am going to check it when I get home, and if it is 5-1/2' long well, then, I will be pretty embarrassed :(

Good catch, BTW ;) !!

Hey, while I have ya - what would be the downside with having the long leg @ 5-1/2' instead of just 4'?
 
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LIScanner101

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Check out this thread, its the best travel scanner antenna I've come across. They are a bit scarce being made for the military but the US Gov bought a bunch of them and they will get scrapped eventually. I think I paid around $70 on Ebay for the one in the thread.
http://forums.radioreference.com/scanner-receiver-antennas/216516-tactical-scanner-antenna.html
prcguy

Yep, I recall drooling over that antenna when you posted that. I searched high and low and couldn't find anything other than a brand-new one and there was no way then OR now I would pay $750 for a portable antenna! Anyway, I'll keep looking.
 

reconrider8

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lol you could buy a couple good quality scanners for that much i wouldnt mind having one either tho LOL
 

LIScanner101

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Well, I checked my wire OCFD and, yep - the short leg is 18", but the long leg is 66", or 18" longer than it should be :(

I cut it down to exactly 48" and will be trying it out again next week in Burlingame CA.
 

nanZor

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GREAT pic!

I did think that the long side was too long, so glad you cut it back to 48 inches.

Mounting it with either the long side or short side up is not a big issue, but as always with the ocfd, try it either way as it may depend on frequency.

Personally, I mount with the longest end up so that the coax is down low for convenience as it makes it bottom-heavy when mounting. GOOD JOB of running it horizontally for a few feet.

I'm also a fan of blue painter's tape. In this temporary setup, what I'd advise is keeping the wire away from the metallic door frame / wall a couple of inches. Rather than tape it to the wall, you may be able to actually hang it from the ceiling without damage with the tape. 1) wrap a few turns of the blue tape near the end of the wire. 2) Use whatever length of tape you need to tape it near the ceiling. 3) Use a small cross-piece of blue tape to prevent the antenna from just pulling it from the ceiling. 4) Don't expect it to stay up for very long. :)

I've also used tie-wraps, or other non-conductive stuff to make a loop at the end so that I could use some twine, thread, or dental-floss to hang stuff. Floss is amazingly strong! And minty-fresh if you like that. For portable stuff with a bit of strength, I'm almost afraid to admit that I use it for antenna purposes. Don't tell people what you are using it for.

Re the Comet at 42 mhz:
Fully extended it is only 40 inches long. For a quarter-wave whip at 42 mhz, you want:

234 / 42 = 5.571 feet (66.852 inches)

I think this may have been where you made the mistake with the ocfd dimensions. Keep that ocfd long side at 48 inches.

So, one option if you use it would be to attach 26 or 27 inches (close enough for rx) to the whip. But use small wire and hang that extension from the ceiling so that you don't stress the thin whip! Ah, back to the blue tape from the ceiling trick and a a few feet of thin bell wire and an alligator clip. Beware of wind!

In a portable op like this, you could just use a bnc with nothing more than 67 inches of thin bell wire hung from an upper support.

Also, if you don't have 67 inches of space vertically, don't be afraid to just take as much as you can vertically, and bend over the rest in an inverted-l shape - ex if you can only run 4 feet vertically, then run what's left over horizontally, but keep it away from the celing by at least a few inches. Obviously we're talking wire here that you can support.

Is that the greatest? NO, but consider that in a quarter-wave whip, the bottom 2/3 of it does the most amount of work so keeping 2/3 or more of it vertical and the rest horizontal is not going to seriously hurt your monitoring.

Purists may disagree.
 
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popnokick

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On the OCFD.... Since the coax feedline is actually part of the antenna at VHF lowband, keeping the coax away from metal frames and walls might help lowband RX. Might be tough to do, but worth a try.
 

LIScanner101

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Thanks to both of you, I appreciate the inputs.

I am usually unable to use the ceiling to mount anything because a lot of these hotels have that "popcorn" finish and nothing sticks to it. I would imagine taping to the window is OK though....??

I will also try to flip the antenna over to get the long side up, I agree this will make it easier to keep the RG-6 coax as perpendicular as possible to the OCFD and make it easier to manage the weight distribution of the antenna.

I have another idea up my sleeve for a travel antenna - gonna try this out on my next trip - stay tuned (no pun intended :wink: ).
 
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