Horizantal/Vertical

[VintageJon]

Running Rat Shack Pro 96 with the 800MHz antenna.

Note that the receiver laying on it's back with the antenna HORIZONTAL get's better reception of APD signals here in Austion TX that with the receiver sitting up with the antenna VERTICAL.

Now I'm an old-fart-kinda-guy and new to UHF-Digital-Trunked, but I'd assumed mobilers were VERTICAL.... (this indicates that they are not!)

In the HORIZONTAL mode you can rotate the receiver 90 degrees of you get bad reception
and often get a good lock. (It seems like the old N/S vs E/W dipole orientation!!)

Anyone else tried this?

-Jon

 

[studgeman]

The typical helical wideband antenna attached to most handheld scanners does not have very good poloriztion isolation. They are a little horizontal, a little vertical. If you were to use an actual mobile antenna, all things equal, you would not have the same results.

All things not being equal, you may be experiencing interference (nextel) at your location, and the change in postion of the scanner is enough to null out some of the interference and increase your SNR. There are quite a few things which could be in play in the scenerio you describe

 

[Al42]

Then again, at 800 MHz almost everything is a reflector to the signal (anything that conducts and is 3" or larger), so the signal may be getting twisted by something locally.

 

[VintageJon]

Thanks for the good info- it's new world in 800MHz when you are used to HF.

-Jon

 

[michaelsbus]

Antenna orientation

If you're a vintage radio guy, then you probably know about ground planes. The RF signal usually travels along tge ground plane from (and ultimately toward) the vertical element.

Inside your portable scanner there's a metal framework chassis. This is your radio's ground plane. You probably will notice better reception while you are holding the radio, as your body becomes inductively linked to and extends the ground plane.

This arrangement is also known as a vertically oriented folded dipole. It's essentially directional for 360 degrees towards the horizon. When you turn the whole mess on it's side, you wind up with the directionality still 360 degrees, but almost half of it is into the ground and most of the other half is toward the sky. The best sensitivity is the two sides going toward the horizon. Your basic dipole antenna.

The next trick: put a slightly longer element on one side and a slightly shorter element on the other, and you got yourself a homebrew beam!

 

[michaelsbus]

Sorry, but...

I just saw a posting of yours on another forum, and I didn't mean to make is sound so simplistic. You obvously know antennae, the only difference at 800MHz is the really short wavelengths. Like mentioned above, just about anything conductive can affect the signalpath. Me, I ain't no genius, but I can get by. Got a ratshack of my own, so I've also experienced some oddball behavior. Consider also design vs. price range of target market. Also consider how they push the "extended warantee" plans.

 

[VintageJon]

Yeah, the "ground plane" is more critical than in 11M due to extremely short wavelength we're working. Also the proximity of almost anything. Present model is hanging from ceiling by 9" of string.
(Have built several successfull 11M and 40M Yagi's and Inverted-V's, but 800 MHz is a bit more touchy.)

I think I'll try a 1/2 wave ground plane for comparison to the 1/4 wave I'm running.

Could be that a 1/2 Wave-Vertical-Dipole could be the ticket. Just a matter of a few BNC jacks, time, coax.

Present 1/4 wave ground plane ain't bad though I really feel I need a ground wire, though I'm just learning 800mHz...

Extended Warrany- not really a bad idea, though parts may go "out of production" after the two years and thus it will pronounced "unrepairable". ARRRRRRUGGGGGHHHHH! (I've seen it before, thanks National Instruments...)
At $500 for a scanner I want all the warranty I can get.

73's,
Jon

 

[jhooten]

It is because Austin leans so far to the left their radio system thinks it is horizontal.

Another quick and dirty test. Take a paper clip and straighten it out, cut to 3.25 in, insert into the bnc connector on the scanner. You now have a quarter wave vertical. If you want to see if a ground plane will have any effect take 3 or 4 more straighted out paper clips and wrap then around the bnc shell on the radio space than evenly around tha connector, and trim to 3.25 inches. You now have a ground plane antenna attached to the scanner. If that improves your reception then you could invest the time to construct or money to purchase an 800 ground plane antenna. Like this one: http://www.universal-radio.com/catalog/scanants/2891.html

 

[JnglMassiv]

It is because Austin leans so far to the left their radio system thinks it is horizontal.

*groan* How long have you been waiting to use that joke?

 

[Al42]

I think I'll try a 1/2 wave ground plane for comparison to the 1/4 wave I'm running.

If you're talking about just building a normal ground plane, but making the vertical element 1/2 wavelength long (extending the radials past 1/4 wavelength will do almost nothing), you'll end up with an antenna with an impedance of approiximately 5,000 ohms. The end of a half wave element is the high imedance point (high E, low I = high Z). That'll be a bit difficult to match.

 

[VintageJon]

Al42- Having thought about it today and realize you are correct. (A lot of what I did in 11M has little use at 800MHz.)

73's-
Jon

 

[Al42]

Al42- Having thought about it today and realize you are correct. (A lot of what I did in 11M has little use at 800MHz.)

Building a half-wave, end-fed antenna on 11 meters would have little use too. The impedance would be about the same.

 

[VintageJon]

Well, the Rat Shack 1/2 wave ground plane worked pretty well for a no-gain omni.
(Of course the 4 element "Moon raker" Yagi was a lot better...)

Perhaps the little top-hat elements that added capacitance were responsible for lo-SWR match on the 1/2-wave ground plane.

As I said I just stick with the 1/4-Wave I home-brewed as it's pretty good, (he said listening to it as he typed this humbel response...)

73's-
Jon

 

[Al42]

Well, the Rat Shack 1/2 wave ground plane worked pretty well for a no-gain omni.

It had a matching network at the fed end.

Perhaps the little top-hat elements that added capacitance were responsible for lo-SWR match on the 1/2-wave ground plane.

A capacitive top-hat just allows you to shorten the antenna. If it was electrically 1/2 wavelength, and the matching network was designed properly, I'd expect the SWR to stay below 1.5:1 across the band.

 

[VintageJon]

That's about what I recall.

Outside Ham input has said that 3/4 wave will give more capture area at 800MHz yet give the same/ or nearly as 1/4 wave! (He could not explain it so I'll searching for theory to back this up.)

Worst case- I have plenty of BNC jacks coming and Imperical Experimentation will reveil! (It was always thus...)

Ain't antennas fun?

73's-
Jon

 

[VintageJon]

Just built another 1/4 wave for use at shop so I can just have one hanging from ceiling at home and one at the shop.

Will report when I have a clear idea of how it works. 800MHz Rubber Ducky is terrible at shop. THis may tell us something...

73's-
Jon