Batboard

looking for some opinions on uhf reapeater antennas and reasons why you like one over the other.

im using a fiberglass omni currently. the repeater is located on the south shore of Long Island. i have no desire for tx rx to the south because its the Atlantic ocean. so my tx rx need only be north west and east. is it posable to set up something like a 4 or 8 bay dipole configured for a N W E patern only?

Look at this page

http://www.andrew.com/products/antennas ... 22-000.pdf

Look down to the DB404L mounted with elements toward the tower (assuming you are using a tower). It nulls out the one side pretty good.

I like the exposed dipoles because I think they must give a little better protection from lightning since the central mast, which is capped with a lightning rod clamp, should carry the current rather than having to carry it through the antenna itself as in the case of a fiberglass antenna. But I think that is probably a relatively minor issue.

Birken

On the Celwave Fiberglass verticals there's a Parasitic Reflector Element that can be purchased and installed on the main antenna. This allows the Fiberglass vertical to produce a cardiod radiation pattern when being mounted at the top of a tower or building structure. These are used on or near Chicago's lakefront two-way transmitter sites.

The main heavy duty Fiberglass verticals being Celwave, DB Products and Sinclair all have superior metal grounding top (caps) to help disappate the "Static" build up on these antennas. As far as direct lightning strikes to antennas, the antenna installation should always have Cad Welded Grounding Wire / Rods at the base of the tower and/or be Cad Welded into the Roof Top Grounding Grid and into the "I" Beams of the building.

The use of commercially manufactured Polyphasers or equivalent "Static / Lightning Protectors" connected to the Heliax Coaxial Feedline prior to entering into the building using large copper insulated plates and Cad Welded to the building's grounding system.

You stated that you're on the south shore of Long Island. If corrosion from salt air is a problem in your area, you may wish to consider an fiberglass enclosed antenna from a longevity standpoint. The exposed dipoles are fine as long as they're not used in a heavily corrosive environment(i.e. industrial, salt spray).

ok. so im going to stay with the omni fiberglass. i want to up the gain. im thinking of using an Andrew Decibel ASP705K. take a look:

http://www.tessco.com/products/displayP ... entPage=12[/url][/url]

with this antenna total hight will be 65 feet from tip to see level with 50 watts in to the antenna. the ERP if my calculations are correct will be 500 watts. the repeater area terrain is totaly flat. im looking to achieve 5 mi coverage on 4 watt HT's.

what do you think?[/url]

In what application are you using these 4 Watt Subscriber units ... Just with a Base Station or Base Station / Repeater System?

If in a Base Station / Repeater System:

What type of Duplexers?

What type of Coax or Heliax RF Feedline are you intending to use?

Is your system located in and among:

1. High Downtown Buildings?

2. Buildings that are 4 stories (45 Feet) or less?

3. Residential Areas?

What is the typical (Summer) Foliage like for Trees and Bushes?

When using the 4 Watt Handheld Subscriber units:

1. Do you intend to use them (TX & RX) at Head level?

2. Or worn and used (TX & RX) at Waist Level with an External SPKR/MIC?

a. Using a 1/4 Wave Whip (6") antenna?

b. Using a Heliflex Stubby (3") antenna?

this is for PS repeated use.

wacom 4 can duplexer

there are 2- 4 to 5 story buildings aprox 1500 feet away but the area is semi urban with few trees mostly 2 to 3 story wood frame houses.

the HT's will be used both a head and waist level with both whip and stuby antennas.

oh i forgot im using 7/8 heliax about 50 feet.

Question: What power limitation is shown on your license? 500W ERP at 50 feet HAAT is going to get out a LOT farther than 4 or 5 miles. I'd be willing to bet I
could hear that signal all the way up on the North Shore with no problem when
you get the machine up and running.

If some other agency shares your frequency, say up in Connecticut or down the Jersey shore, you could have problems in both directions with the setup you're contemplating.

I'm originally from East Rockaway and I know your area's RF conditions. I was
able to work a good 50 miles years ago on VHF AM with 5 watts and a unity
gain groundplane located in the attic.

The main heavy duty Fiberglass verticals being Celwave, DB Products and Sinclair all have superior metal grounding top (caps) to help disappate the "Static" build up on these antennas. As far as direct lightning strikes to antennas, the antenna installation should always have Cad Welded Grounding Wire / Rods at the base of the tower and/or be Cad Welded into the Roof Top Grounding Grid and into the "I" Beams of the building.

I have a heavy duty celwave that took a direct hit, the top cap has a arc scar and the antenna no longer has DC contunity to the mount. The strike also blew the 1/2 jumper connector at the connnection to the 7/8. The system has Polyphaser protectors mounted in a well grounded protector plate. A computer monitor in the transmitter room had to be degaused several times due to the field this strike imposed on the radio room ground wires. The Quantar that is on this antenna was not damaged.

As to high gain (50 watts in 500 ERP) you may not get the close in coverage with this setup. Look at the antenna patterns, the high gain antennas have almost no coverage under the tower but are great 50 miles away.

I also have a system on the South Shore of LI and found a 3 to 5 DB antenna at 100 feet covers better than a 10DB in the local area. Our CoChannel in New Jersey still hears us either way. Do not get carryed away with Gain, sometimes it can hinder rather than help.

Tom in D.C. wrote:If some other agency shares your frequency, say up in Connecticut or ...

What frequency is this?

Has anyone tried using the Bluewave antennas? I'm looking at the Summit folded dipole series and they look VERY heavy-duty.

For VHF we use mainly BA1010s and 620 super heavy-duty fiberglass antennas at mountaintop sites because they're the only antennas that stay up through years of heavy rime ice buildup. However these Bluewave antennas appear to be well built for heavy ice loading conditions (on paper anyway)...

http://www.bluewaveantenna.com/products/summit.html

Hello Devin,

Here’s what I would suggest to do so with your Fiberglass +10 Gain Antenna idea ... change it to a lessor amount of Omni Directional Gain some thing around +5~6 dB Gain Maximum. Using a +10 dB Omnl Gain antenna is an over kill for the RF system coverage you’re requesting and probably would cause more co-channel interference that you do not want or need.

I’ve based my Path Losses upon the information that you have provided, with the two exceptions the antenna and the feedline. I used only a +5 dB Omni Directional Gain Fiberglass antenna rated at 150 RF Watt Power Level because of the RF 50 Watt Transmitter Output Level. You do not need an antenna that is RF rated at 500 Watts unless you were using a 250~350 Watt RF Output Power transmitter; and then it would be still questionable because of RF Losses through Duplexers, Circulators and Heliax Feedlines. I also changed the Heliax from 7/8” to ½” because the RF system does not require the larger coaxial cable to reduce losses only by .5 dB maximum! You could not detect that little amount of signal difference when using the system.

Building Losses.......................................................-10 dB
Foliage (Tree & Bushes).........................................- 6 dB
Subscriber at Waist Level & Stubby Ant...............-13 dB
Duplexers.................................................................- 2 dB
1/2" Heliax Feedline...............................................- 1 dB
Total Losses............................................................-32 dB

+5 dB Gain Celwave PD201....................................+ 5 dB
Repeater's Rcvr Sens: .25uV@12dB SINAD............+ 6 dB
Total Gain..................................................................+11 dB

Total RF System Losses.............................................-21 dB

UHF Repeater RF Output 50 Watts, Antenna @ 60 Feet

The RF Analog System Coverage is based upon the older /\/\ system coverage calculator which many technical people may disagree with and rightfully so with their opinion if they have the latest and greatest RF coverage software programs.

The following coverage provides you with an idea how well the Subscribers units will access the UHF Repeater:

90%/10% This indicates the Subscriber units will be able to access the UHF Repeater Coverage 90% of the time with a 10% chance of Dead Spots / No Access Probably.

70%/30% This indicates the Subscriber units will be able to access the UHF Repeater Coverage 70% of the time with a 30% chance of Dead Spots / No Access Probably.

50%/50% This indicates the Subscriber units will be able to access the UHF Repeater Coverage 50% of the time with a 50% chance of Dead Spots / No Access Probably.

90% RF System Coverage Radius from the Repeater is 6.5 Air Miles

70% RF System Coverage Radius from the Repeater is 9.8 Air Miles

50% RF System Coverage Radius from the Repeater is 14.2 Air Miles

Another alternative would be to use a +3 dB Omni Directional Gain antenna and decrease the RF System Coverage to:

90% RF System Coverage Radius from the Repeater is 5.5 Air Miles

70% RF System Coverage Radius from the Repeater is 8.6 Air Miles

50% RF System Coverage Radius from the Repeater is 12.2 Air Miles

Dan

thanks dan for the info. thats just what i needed to know.

the only reason im using 7/8 is because i want to use hard line and i got it for almost nothing. nice to have friends ya know.

Fiberglass antennas always get hairy. Metal antennas never get hairy. I like DB4xx series meself.

I have replaced the coaxial cables on DBs before(salt/corrosion environment). I'm not sure they're available anymore since Andrew came in.

FWIW I prefer Celwave exposed dipoles when they are available...at least I did prefer them...what with all the mergers/buyouts it is never sure who owns what any more or if it is even made...anyway the things I like about the Celwave are that the center conductor portion of the dipole element points down instead of up...gives a little more edge on lightning in my book to have the grounded portion up...and also the harness is run inside the mast...and also the hardware is quite a bit thicker/heavier. But they make no UHF antenna that I am aware of, this is all high band I am speaking of, for general reference.

Birken