[Scanner] Stoopid antenna questions
Edmund F Leavitt
[email protected]
Sat, 12 Apr 2003 20:13:35 -0700
Phil,
Like so many things, you have to make compromises. If you want broad
band, you sacrifice somewhat on gain. If you want to work several
bands, a multiband antenna may be best, but if you are looking for truly
boadband performance, and vertical polarized omnidirectionality, it is
really hard to beat a discone.
The discones I have played with seem to display a sharp fall off on the
low end, but roll off very gracefully as you go up in freq. Years ago I
saw an ad for one from...dare I say it...Radio Shack. With great
skepticism, I checked it out. It was mostly stainless steel and well
built. I bought two. (Disk radials = 11 inches, cone radials = 32
inches.)
I 've used them several times when it made sense. I put one into service
first as the catch all antenna for those in between freqs at work.
Somewhat later, in a disaster relief effort down in Texas I put one up
so that I could work 410 MHz federal freqs and HAM 2 meters with the same
antenna. (There are a lot of dual band 144/440 antennas, and 150/460
antennas, but not very many options for 146/410.) It worked very well.
I've swept one of the R/S discones with an HP system analyzer. The
antenna in question was spec'ed for 140 MHz to 1.2 gig if I recall. It
has a sharp cut off around 110 MHz. But at the high end, it does really
well up to 3 gigahertz. Expect gain comparable to a 1/4 wave antenna
across the whole range. I work MF, HF, VHF, and occasionally low UHF. I
rarely go above 800 MHz, so I can't tell you how much you will find at
the high end of your receiver. My impression is that there isn't much of
interest above 1.2G, but that may be based on my own ignorance.
As for feedline, I would recommend you take a hard look at what you are
using if you operate in the UHF part of the spectrum. Losses climb
rapidly as you go upward. I would gravitate to a good low loss RG-8
style...preferably Beldon-9913, -9913F7, or whatever your budget will
tolerate. If the feedline is fairly long, hardline is even better.
As for connector series, you are right that UHF / PL-259 connectors are
somewhat inferior. Even with some improved construction, they were never
designed for UHF operation. Unfortunately they are cheap and therefore
all too plentiful. A change to BNC or perhaps N wouldn't hurt, but I
wouldn't lose sleep if you can't get that done.
Last thought: give your IsoPole a hug for me. My first factory made Ham
antenna was an IsoPole. I still have a very high regard for those. A
friend put one up a year ago and continues to be astounded with its
ability over a 70 mile path. They are funny looking, but who cares?
****************************************************************
Edmund Leavitt Ph: 253 582-5034
Ham/MARS/SHARES: KA7UKN / AFA5AH / KPS654
Lakewood, WA N 47� 09' W122� 31'
On Sat, 12 Apr 2003 21:21:32 -0000 "Phil Atchley" <[email protected]>
writes:
> Hi.
> I'm new to this list but not new to radio (mostly HF) having 40+
> years of RF
> experience.
>
> Anyway, I've never been a big one on listening to anything much over
> 30MHz
> though I've played around with a few old scanners and 2mtr rigs.
>
> HOWEVER, all that is about to change. A friend just shipped a New
> Yaesu
> VR-5000 wideband receiver (100KHz to 2.6GHz) to me. Yes, from what
> I've
> read it isn't the 'best' DC-daylight set around, but it is a gift!
> Now I
> need to augment my antenna farm consisting of a 65 foot sloper,
> Hustler 6BTV
> vertical AND a homebrewed active probe for VLF/Longwave beacons. My
> primary
> listening interest are NDB's (longwave beacons) at the present
> time.
>
> Most of my career I was in various RF fields. I.E. Point to Point
> Microwave, HF, Satellite etc and I know how important good matching,
> low
> loss cable etc is at these higher frequencies. HOWEVER, my
> retirement
> budget is severely limited, ruling out hardline, expensive antenna
> systems
> etc.
>
> With this point in mind I'm considering obtaining one of the
> various
> discones on the market, hopefully used. This will be mounted above
> the
> mobile home roof at a height where a 20 foot coax cable (already on
> hand)
> will reach it, putting it some 13-14 feet above the roof. (An
> Isopole
> antenna in the same location gave me about a 35-45 mile range to
> mobiles on
> 2 meters).
>
> Antenna Questions.
>
> 1. Most of these discones operate about 100-1200MHz (some claim
> down to
> 30).
>
> 2. Is the upper limit a sharp cutoff or does it roll off
> gradually?
>
> 3. As the receiver goes to 2.6GHz can I expect any response from
> one of
> these antennas up there.
>
> 4. The receiver uses a SO-239 connector (UHF connector ??) as do
> some of
> the discones. Can I 'really' expect to push 1300-2600 MHz through
> these
> things? (Some folks change the receiver connector to BNC)
>
> 5. The Coax I have on the antenna in that present location is a 20
> foot run
> of good quality RG-8X. It 'seemed" to work well on the 800 MHz
> sheriffs
> department frequencies when I had my 2mmeter "Isopole" up there.
> YES, I'd
> like to eventually get some better coax, but anybody have any idea
> of how
> much loss I might expect on this "hunk" with the two PL-259 plugs
> and how
> high in frequency I might be able to get away with on it???
>
> 6. And lastly, what antennas do most of you use to listen in the
> 1200-2600MHz range? I don't see much out there and I know they are
> probably
> pretty exotic in price. Or do you just make a smaller discone or
> something?
>
> 73 de Phil KO6BB
>
> ********************************************************
****************************************************************
Edmund Leavitt Ph: 253 582-5034
Ham/MARS/SHARES: KA7UKN / AFA5AH / KPS654
Lakewood, WA N 47� 09' W122� 31'
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