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Author Topic: V/UHF antennas other than Disconeys  (Read 1075 times)

Offline Josh

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V/UHF antennas other than Disconeys
« on: June 21, 2019, 1802 UTC »
Are there other passive broadband V/UHF antennas than the lowly Discone? I've often used HAM multiband vertical antennas such as those made by Comet, Diamond, and so on for scanning, but they show pronounced peaks only at the HAM bands and only by coincidence is there low swr elsewhere in the spectrum. Staying away from active antennae for now.

Any input appreciated.
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Offline JimIO

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Re: V/UHF antennas other than Disconeys
« Reply #1 on: June 22, 2019, 1651 UTC »
There's it's brother the Bicone https://en.wikipedia.org/wiki/Biconical_antenna
It's more difficult to build and has no real advantage over a Discone.
And the Vivaldi Antenna or Tapered Slot Antenna which is directional and not practical below about 700 Mhz. So the short answer is NO.

Offline Josh

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Re: V/UHF antennas other than Disconeys
« Reply #2 on: June 22, 2019, 1816 UTC »
Hmmmm. I'd forgotten about the cage dipole for v/uhf aka bicone, thanks! Also had forgot about the Vivaldi type too!
Some folks have used old tv yagis, they cover a decent amount of spectrum and when mounted vertically they more or less respond well enough for local sigs off the sides and back.

I think what's going to go down is a set of verticals sliced for the bands of interest, all attached to the same feedpoint. When one vertical is a halfwave and thus hi z for the tuned freq, hopefully another vertical will be lo z at a quarter wave or other odd multiple. Then again, this may not be an improvement over the lowly discone.
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Offline JimIO

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Re: V/UHF antennas other than Disconeys
« Reply #3 on: June 22, 2019, 1854 UTC »
"I think what's going to go down is a set of verticals sliced for the bands of interest"

That would be This:

   https://en.wikipedia.org/wiki/Log-periodic_antenna

This is a good site:

   http://www.antenna-theory.com/
« Last Edit: June 22, 2019, 1906 UTC by JimIO »

Offline ThaDood

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Re: V/UHF antennas other than Disconeys
« Reply #4 on: June 22, 2019, 2322 UTC »
For years, Channel Master had that base scanner antenna that was a fan VHF / UHF fan dipole, and it looked like a squashed star, but was very popular. Many municipalities used them. I have heard of folks TX'ing on them, albeit 20W, or less, since they had matching baluns on them. My 1st outdoor wide-band VHF / UHF scanner antenna was just a 30" car antenna 30ft up a fur tree. That actually worked great to RX 37MHz EMS, 46MHz fire, 35MHz McDonalds drive-through, 46 / 49MHz cordless phones, 2M HAM, VHF high police, fire, businesses, Conrail trains, VHF AM airplanes, (Especially the chit-chat 123.450MHz FREQ.), even 170MHz radio station remote broadcast links, and UHF HAM, business, GMRS, and TV audio.  Ya know, it wouldn't be hard to make such an antenna. 
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Offline Josh

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Re: V/UHF antennas other than Disconeys
« Reply #5 on: June 23, 2019, 0716 UTC »
Didn't want to go active but some of them minicircuits lna amps have more dynamic range than a lot of radios, and very low noise figures. Something like that could make up for a deaf disconey.
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Offline ChrisSmolinski

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Re: V/UHF antennas other than Disconeys
« Reply #6 on: June 23, 2019, 1243 UTC »
I have my discone hauled up to the top of a tree, along with a pre-amp right at the antenna. I can just pick up the Frederick MD AWOS on 124.875 MHz, not a bad haul, it is about 30 miles away.

At VHF/UHF you want height height height.
Chris Smolinski
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Offline pinto vortando

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Re: V/UHF antennas other than Disconeys
« Reply #7 on: June 23, 2019, 2124 UTC »

At VHF/UHF you want height height height.

^^^ this
Das Radiobunker somewhere in Michigan

Offline Josh

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Re: V/UHF antennas other than Disconeys
« Reply #8 on: June 24, 2019, 0523 UTC »
Think I'll try the discone plus amp plus fmbc trap plus height. A log periodic could be mounted vertically and garner some omnidirectionality but it'd still have a favored direction.
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Offline R4002

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Re: V/UHF antennas other than Disconeys
« Reply #9 on: June 24, 2019, 1230 UTC »
Think I'll try the discone plus amp plus fmbc trap plus height. A log periodic could be mounted vertically and garner some omnidirectionality but it'd still have a favored direction.

Indeed.  I've done several quasi-experimental tests with the VHF and UHF bands involving simple vertical 1/4 wave and 5/8 wave base station antennas and at VHF (151 MHz, specifically the MURS frequencies) even getting the antenna 2-3 feet higher than it was previously make a noticeable difference with distant stations.    I have good experience with discones, I'm sure you all remember the scanner discone RadioShack used to sell with claimed 25-1300 MHz frequency coverage.  It did excellent on VHF low band for receive purposes and even better on the VHF/UHF/800 MHz land mobile radio bands and the VHF and UHF AM aircraft bands.  For broadband omnidirectional I think its pretty close to the best you can do.  I believe the military make extensive use of the discone design for both UHF-AM 225-400 MHz and VHF-FM 30-88 MHz broadband coverage with frequency hopping radios.  For fixed frequency (single channel) use, my understanding is the RC-292 style vertical with ground planes is considered the ideal omnidirectional antenna. 

I don't know if you live in an area where the 152.480 MHz to 152.840 MHz band is still used for paging (FCC Part 22 - in some areas the frequencies are slowly being repurposed for land mobile) but a filter that knocks out those frequencies could be helpful if there's still high power pagers in your area.  I know in lots of places pagers are completely gone from 152 MHz and are all on 900 MHz.  Since I know UHF mil air is one of your monitoring targets, taking out strong signals that have second harmonics in the 304 MHz to 306 MHz band could help you dig out distant signals.  If there's no paging on 152 MHz in your area (or, if there is a monitoring target on 152 MHz in your area), then don't worry. 

FM BC trap is a very good idea regardless, especially if you're planning on running a preamp. 
U.S. East Coast, various HF/VHF/UHF radios/scanners/receivers

Offline ChrisSmolinski

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Re: V/UHF antennas other than Disconeys
« Reply #10 on: June 24, 2019, 1450 UTC »
I had one of the Radio Shack discones for... wow, 25 or 30 years before it died (elements starting falling off). I replaced it with this Sirio discone last year: https://www.amazon.com/gp/product/B008899J8Y/ref=oh_aui_detailpage_o00_s00?tag=blackcatsyste-20

It has a very good build quality.

Years ago I also had one of the Radio Shack ground plane antennas, which did a little better on the low bands due to the larger size. 

Discones don't appear to be too magical in design, I suppose you could build your own and perhaps a larger one would work better on the low bands.

Here's a photo showing my discone in the tree, the dipole below it is the 80m:



I might be able to get it higher in the tree if I can shoot a line further up, although the branches are not as strong up there. There's likely some attenuation from the leaves and branches, which is less of an issue in winter. I think it is around 40 ft high now.
Chris Smolinski
Westminster, MD
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Offline ThaDood

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Re: V/UHF antennas other than Disconeys
« Reply #11 on: June 24, 2019, 1732 UTC »
I used one of those RS Discones as well from the late 1980's. Later, it was my 1st TX / RX multi-band antenna for 2M, 222MHz, and 440MHz. Buy yes, those aluminum radials just broke off too easily. So, now I'm using the Diamond J130, with 6M VERT stinger. It's what I use now for 52.525MHz, 2M, MURS, 222MHz, and 444MHz, but doesn't seem to match on GMRS 462/7 MHz. And, its low gain makes it so that I can defract out of this valley.   
I can't decide upon what's worst, young and stupid, or old and chemically dumbed down.

Offline Josh

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Re: V/UHF antennas other than Disconeys
« Reply #12 on: June 24, 2019, 2010 UTC »
When I was in ems and had a rural run far from the repeater, I learned how 3 to 6 additional inches height can be the dif between copy and no copy at the repeater.

Also learned about knife edging, can't hit the repeater from atop the rise? Move if possible to the side of the rise away from your intended rx site just below the crest so the antenna is actually slightly below the crest, and try again.



I left out the highpass filter to the above list of ingredients.
Discone (have a diamond or comet somewhere around here with the lowband vertical element), 25/30mHz highpass filter, fmbc trap, amp, 9913 to shack, heat, serve, enjoy.

There's a few pagers in the 150mHz range but not objectionable and 15 miles away, far higher powas are found at ambc and fmbc than pretty much anything else around here. Wonder if I can get some hardline for free somewhere!
« Last Edit: June 24, 2019, 2016 UTC by Josh »
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Offline i_hear_you

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Re: V/UHF antennas other than Disconeys
« Reply #13 on: June 24, 2019, 2032 UTC »
now I'm using the Diamond J130, with 6M VERT stinger

I have one of these up at about 35' and fed with LMR400.  I can hear about half of the Chicago Police Department dispatch frequencies from about 43 miles out, and I can activate a few Chicago-based repeaters with 75 watts on VHF. I hear even further into Wisconsin.  Overall I'm impressed with the discone, and it is keeping me operational while I save money for a rotator and some yagis.

I have a small LNA and power injector kit and I'm curious if they can make my ears even bigger.

Offline Josh

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Re: V/UHF antennas other than Disconeys
« Reply #14 on: June 24, 2019, 2243 UTC »
"I have a small LNA and power injector kit and I'm curious if they can make my ears even bigger."


There's a thought. If you add a lna you can't tx with that antenna anymore. I've a burned out 2m preamp I could get the cor sense fixed, pipe in a wideband lna in lieu of 2m only, and presto, tx sensing wideband preamp!
Conveniently located near Vincennes Indiana.