Batboard

I am finding a number of dead spots with my current antenna. Presently the first site is on the roof of a 6 floor offise building next to the HVAC units. The building is approx 350' above sea level and I am using a DB-411 offset dipole. great for distance but local communcations is hit or miss. The terrain covered is basically sea level within a 1/3 mile and a northwetern ridge 30 feet above the site. Antennna Db 9 with 100' of 1/2 hard line. The area is hilly due to river valleys.

I have been told that antennas with an adjustable downward tilt could reslove some of the close in prolems.

The Second site has similar issues and is using a DB 404 omni antenna db 4.8.

Both repeaters are gr1225 puting out 30-35 watts at the duplexer.

The basic pproblem for site 1 is I can talk from 25miles without a problem but a 1/4 mile can't hit the repeater due to the shadow of the hill.
Site 2 has a similar issue but distance is very spoty.

Should I invest in an omni antenna with downward tilt or is ther a differant antenna that will improve my situations.

My base ERP is 90 and 60 watts with a plan to upgrade 1 reater to a MTR3000 next year

A voting system in on the back burner

Any ideas

Mark

You really need to make a horizontal plot of the area your trying to cover and see what it looks like. Down tilt
may or may not help and could cause your distant coverage to go away. It needs to be done with good info
in hand and not just do it and live with the results.

I have spent about 15 years of my life working on cellular site design and coverage in some other jobs. The
design of the antenna systems. A good deal of effort goes into getting the signal to go where you want it.
Down tilt gets used, but you have to be careful that you don't over do it. Also the use of lower gain antennas
will provide better close in coverage. You do however loose some energy out on the horizon with the lower
gain antennas. If you over do the down tilt to get close in coverage, you will loose on your distant coverage.

Going back to the problem your having, by any chance does the building your having the coverage issue
from have a parapet wall around the edge of the roof on the building? These walls can cause a good amount
of shielding to the close in coverage. The solution is to mount the antenna closer to the wall in the direction
your having the issue with or raise the antenna enough to be able to have line of site to that area.

Jim

emtprt wrote:I am finding a number of dead spots with my current antenna. Presently the first site is on the roof of a 6 floor offise building next to the HVAC units. The building is approx 350' above sea level and I am using a DB-411 offset dipole. great for distance but local communcations is hit or miss. The terrain covered is basically sea level within a 1/3 mile and a northwetern ridge 30 feet above the site. Antennna Db 9 with 100' of 1/2 hard line. The area is hilly due to river valleys.

I have been told that antennas with an adjustable downward tilt could reslove some of the close in prolems.

The Second site has similar issues and is using a DB 404 omni antenna db 4.8.

Both repeaters are gr1225 puting out 30-35 watts at the duplexer.

The basic pproblem for site 1 is I can talk from 25miles without a problem but a 1/4 mile can't hit the repeater due to the shadow of the hill.
Site 2 has a similar issue but distance is very spoty.

Should I invest in an omni antenna with downward tilt or is ther a differant antenna that will improve my situations.

My base ERP is 90 and 60 watts with a plan to upgrade 1 reater to a MTR3000 next year

A voting system in on the back burner

Any ideas

Mark

I agree with everything Jim said and would add:

The DB404 should have good close in coverage if it's configured as an omni with the two pairs of elements at 90 degrees to each other. If they are in the same plane, it's elliptical.

The DB411 is great for distance but probably would have difficulties close in as it shoots over your head. You can rearrange the elements to give better omni coverage.

Considering you're using GR's, and probably using the standard duplexer that comes with the model, you should do a rcvr desense test to determine your effective sensitivity. You may be impaired by other local repeaters and not know it.

In my experience you should only have 20W to the antenna through the duplexer. The xmit pwr may be set too high, and will cause premature failure.

PM me with your lat & long, building el, other specifics, etc, and I can create some plots for you.

The antenna is currently 10-12' above any obstructions and we have an swr of "0" back via a Bird watt meter.

The Lat. Log 41-17'42.94N 73-05'00.86W Alt. 385' if you look on Google earth it is the Center building at 27 Waterview 4 floors 2 sub-floors
Poor covereage area .75-1.75 miles North


Thanks
Mark

These are pessimistic plots. Your actual effective range is probably greater than this. Green is good. The signal is at least 15db greater than the rcvr threashold. Yellow is fair 0db to <15db greater than rcvr threashold. Those are the areas subject to noise and flutter.

Here's your repeater transmitter assuming UHF 450-470mhz, 30W into the duplexer, 4db loss through the duplexer and 100ft of heliax, 9db offset antenna with an azimuth of 180 degrees, building height of 70ft with a 10ft mast, and a UHF portable with -115db rcvr sensitivity at 5ft elevation and a standard antenna.



Here's your rptr receiver assuming 4W portable and a rptr rcvr sensitivity of -115db.



It definitely shows an area of poor coverage north towards the river. It's in a hole obscured by the hill the continues to rise north of the building. The landcover data says it's well forested with mixed hardwood, some urban clutter, and the antenna doesn't clear the tree canopy. If you raise your antenna another 20ft, reduce the gain, and change to an omni pattern you should see some improvement. You should consider doing a desense test to verify your rcvr isn't getting clobbered. If you can tell me what the effective sensitivity is, I can plug that in to see how it affects the plot.

I am revisiting the site Thursday or Friday and should be able to get the info for you. I am unable to raise the antenna height due to the building owner's guidelines.

I'll keep you updated

Thanks

That is often the case. Goes to visual blight, building aesthetics, etc. They don't want a cluttered roof. That model antenna has a rather long pipe. If you rearrange the elements into an omni pattern, place the top element towards the northern area that needs filling.

The antenna in place does not allow for pattern change (DB 411) but I am considering a lower dB omni either dipole(DB-404) or fiberglass low gain antenna. The smaller antenna might allow me to use a longer mast and keep the building owner happy (there are 2 22' antennas on the same roof).

We are attempting to find funds for a tower at the north end of the parking lot but that is years away. The elevation at the proposed tower site is a bit higher and should clear the hill/ trees.

A voting receiver is on the short list for funding at this point but not until the repeater is replaced. Motorola does not support a voter for the present device.

I drove around yesterday and the maps are amazingly accurate. Nice software program.

Thanks for the help

Mark

You're welcome. Glad to help.

I was going to ask for a sanity check on the maps, but I wanted to see the area of interest by setting it for 99% coverage. When I set it to 70%, which is acceptable for most users, then the total footprint increases quite a bit depending on terrain. However, it tends to mask close in problems. I can show you the difference later.

Too bad about the antenna. Sometimes the elements are held on with hose clamps allowing you to change the pattern, and sometimes it's drilled and bolted making change difficult. That style antenna is typically used by paging companies at one side of their intended coverage area meant to blast in, give good building penetration, and talk to the horizon. It's not so good for repeaters unless you can gain enough elevation to be well above your service area, and are 10 miles away so the beam has an opportunity to hit the dirt.

No. You're right. GR's are not meant for tone or local control without some effort, and don't easily work with a voter.

Here's what your lower gain antenna should do for your rcvr. A little fill close in. It's subtle, but noticeable.

Here is the absolute best you could expect out of your current configuration. I widened the area, and turned on red to make it easier to see the dead spots close in.

Just my $0.02 on antennas, never use a exposed elements in any place that gets wet... go with a fiberglass encased antenna.
Exposed elements will cause you grief a few years after you have this system in place, I see it all the time.
Every chance I get to pull an exposed element antenna out and put in a fiberglass encased one I do.

Andrews suggests that you do PM's that type of antenna every 6 months or so, unless you like rebuilding antennas...

>>>Hardwire<<<

I have an account with Tessco and have been comparing antennas for the site.

I spoke with an engineer from Laird regarding their Mountaineer Series but he informed me that they discontinued the line. I am trying to get the most bang for the buck at this point. In the past we have used the Andrew DB dipole array antenna at the recommendation of the local radio shop. No real problems with the product just some postioning realginment due to high winds (Tornado) last year.

If anyone can recommended an antenna I am open for suggestions. I realize that I will need a lower gain antenna for the local coverage and when the repeater is replaced the power will need to be increased for building penetration.

I did contanct Comprod, they make custom antennas, but I have not received a quote or type of antenna that they could provide.

Mark

I spoke to an engineer from Comprod in Canada and he stated what I've already realized "I am over shooting the locations at the base of the North Hill. He suggested a 0 DB gain antenna with added height or a phasing harness and adding a low or 0 gain antenna to work in conjunction with the present antenna and increasing the output power of the repeater.

The present antenna will cover distance and the 0 gain will cover the local area with an approx. loss of 3db.
I have seen this is done for TV reception and for inside building /campus type low power systems covering schools or hospitals but not for large area communications.

Has anyone worked with a dual antenna system to cover an area of 10-20 miles?

Mark

I'm partial to the folded dipole. Love it in fact. It's quieter and talks further db for db compared to colinear. It's not fond of falling ice however. OTOH, I've seen fiberglass antennas pogo through a shelter roof after the wind snapped them. Everything breaks.

I've done dual antennas. Usually it involves a yagi to put gain where I want it. A phasing harness or a power splitter to an omni and a yagi lets me cover an industrial yard and blow through the fab. Back to back yagis are great for covering a coastal highway caught between the ocean and a mountain range. I never use big gain. Just enough to put the energy where it will do some good.

I already have a 11db yagi and the harness is around 100.00 I might give it a shot . Right now i'll loose poer from the limitations of the 1225 repeater but when the new 100watt repeater is at the site I should be in good shape.
I am visiting the site at 10:30 Friday and will look for a mounting point to set up a 20 foot mast and to setup the Yagi.

Should the Yagi be positioned horozontal or vertical for the best coverage through the northern hill I have to deal with in order to cover the lower elevations?

My calcs say if you just rotate the antenna with the elements at 330 (approximately NW), you should see some difference. An 11db yagi might be a bit of overkill.

I keep forgetting to ask - what direction they are pointed now?

The DB-411 om 454.000 (dipole array ellipitcal 9.6db) is pointed NNW right now. I had 2 people with portables talking to me when I aligned the antenna. The first was in the river bed 1.68 miles north of the site the other was NE 4 miles in a previously known dead area. The test was done after the antenna was raised 8 feet form it's oringinal height.

The repeater was moved to it's present location at Thanksgiving time. A donated antenna was given to use at the present locaction. The previous location was at 41-18'28.64N and 73-05'19.75W at 291 feet above sea level with a 10 foot mast and a 5db gain omni fiberglass antenna. good east and north local coverage por sout and west coverage.

Our other repeater (451.550 )has a DB 404 omni dipole array with 3.8 at 41-19'09.13N and 73-43'03.29W 432 ft on a 35 foot tower. Poor coverage same river area and and Rte115 along with scattered spots through the entire area including NE

I'll plot the other locations tonight. Here is a side by side of a yagi and the elliptical aimed at 330 with coverage color enhanced so you can see the effects. I don't have a way to plot both antennas together.

Today I turned down the repeater power and some of the areas that hand marginal portable coverage improved slightly. Distance coverage with a mobile seems unchanged. The sound quality of the repeater has improved with the power change also. The duplexer was more then likely being overloaded.

The Maps have been great. I spoke to someone that presently has a narrowband MTR2000 set at 100watts with a 10db gain 22' omni at the same location. He is going to provide me with the studies that were done a few years ago from the present site. I shared my current experiences and future plans. He stated that his coverage in my locations of concern were improvrd with the higher power and larger antenna.

I am looking forward to compare the studies. He asked which program was used to generate the data that has been provided.

Mark

Good morning Mark. I'm using Radio Mobile freely available at cplus.org. Very good program, and well supported by the group.

So, I have a question - You turned down the transmit power out and portables could talk in better with less noise? By how much did you turn it down?

Sounds to me like you should have the duplexer checked. The reject duplexers that come with the GR series can handle all the power the transmitter puts out without a problem. Like all duplexers they do have to be tuned spot on to have the best performance. The least little xmit energy getting into the rx port can cause desense and a loss of rcvr range without affecting xmit range.

The rfpa could have been spurious. I generally set a GR for no more than 25 watts out of the rfpa into the duplexer to preserve the pa, and lengthen their lifetime. I've never seen one get spurious, but there is always a first time. Then again, if the duplexer is slightly off, and the pa was looking into a mismatch while set for full power, it's hard to say how it would behave. It may have generated quite a bit of noise until you turned it down.

Check your duplexer cables as well. A slightly loose crimped shield or a center pin pulled back a millimeter can cause enough noise to clobber you.

Do you have a friendly two-way shop you can take it to who will check your duplexer and your GR for little or no money? Might be money well spent. I'd do it for you, but I'm on the other side of the country. Shipping costs would almost equal what a local shop would charge, and turn around would be much quicker. It is an option I'll offer you if you do not have someone you can rely on already.

Post duplexer was 35 watts pre was 58 watts.

I decreased the transmitter. To 40 watts and the duplexer is 28 watts out with 0 SWR back.
The next plan check rooftop jumper and output at antenna.
I had the duplexer retuned from 453.050 to 454.000 recently by Motorola.

Rut roh! You got more than 40W out of a GR transmitter? No kidding? I'll have to check that out some time. That may well be the problem. Did you happen to check vswr between the transmitter and the duplexer?

I checked tx to antenna and then duplexer out to antenna inside the building pre-polyphaser.

The twin repeater is running 27 watts post duplexer with a 3.8 DB-404 antenna and has been rock solid for 10 years. It is at another location and has geographical deadspots that are expected due to it's location.

I have had Maxtracs/GM300, M1225 and CDM1250s run 10-15+ watts above rated power before (either out of the box or used items that I have picked up). I try to keep the radios within Motorola spec. when they are placed in service and I do turn the power down if I discover a high power condition.

Interesting (Spock eyebrow). I know my wattmeter is a little pessimistic which is why I rely more on my service monitor to tell me what the xmit power is. I'm hoping your wattmeter is an optimist.

I plotted your other station in New York, and made an interference map that shows where the two overlap. Blue is NY, green is CT, and black is where they have equal signal strength. This mode has fairly high confidence meaning it tends optimistic. But, the granularity is very fine giving great detail. The ridge between them does a good job of keeping them isolated. And then all the rolling hills make good coverage impossible. All the more reason to keep your gain low and your elevation high.

The other map showed your transmit overlap. Here is your rcvr overlap.

Mark - with the correct lat-long you sent me, I replotted the second rptr. though they are just across the river from each other, and at about the same elevation, the Waterview site has much better performance than the Humphrey site because it's antenna is above the surrounding urban buildup, and tree canopy. The Humphrey's 35ft tower is getting shadowed badly. That said, it does serve some parts of the area better.

Here is a similar interference map. However, rather than showing where the two sites overlap, it shows where one serves better than the other. This is the rcvr map.



Here is the xmit map.