Tower and 7/8" hardline instalation, dual band operation on single antenna

[dksac2]

Unless I'm wrong, 50 watts ERP is the max you can run using GMRS. Your answer is going to be to figure the combination that will give you as close to 50 watts ERP at the antenna as possible.
50 watts ERP is a decent amount of power. What you really need to do to make this work is to get your antenna as high as possible.
When it comes to the GMRS, at 50 watts, it will talk as far as the line of sight plus a little, so adding more power is not going to make a lot of difference. If you have a lot of mountains, more power could help with signal bouncing off of the mountains, but in a more flat area, 50 watts and height will get you the most distance. You could have a 200 ft tower and 50 watts will talk as far as the line of sight from the tower, more power is not the answer, antenna height is.

John

 

[Logan005]

Yes. Tower top amplifiers are used on the commercial side in some installations. I have a tower top amp on the receive antenna for my 800MHz system to boost incoming signals and it works well.
Tower top amplifiers for the transmit side are available. For a single antenna, they will amplify the outgoing transmission and preamp the receive. For GMRS, you need to read the rules regarding maximum transmitter output. ERP isn't an issue, however. Ham you won't have an issue. These amps are not cheap. The one I purchased for the receive side of my 800MHz system was just above $5000, not including installation.

so you use separate TX and RX antennas in general? on 467 and 462 how far apart must the antennas be from each other? Vertical dipole from another vertical dipole and another yagi? or other combinations. I have looked at several base of tower environmental enclosures, I like the boxes similar to the traffic light boxes that open on both sides. obviously I am not spending 5k on a tower top transmitter. but I bet I can pick up an old traffic light switch box at a county auction. in the distance I see several of the big towers have two tip top antennas, they are spaced on a hoz beam. is that how I will space the dipoles if I use separate antennas.?

 

[Logan005]

Thank you again John: dksac2, I am in south florida, 50' is above 90% of everything here. I do consider downtown fort Lauderdale as an obstruction, but it is a small area of tall buildings. not too concerned about south and west of the city anyway. 50' is my limit for the near future. but my understanding of this type of setup is greatly improved. in the middle of thunder and lightning here now, but I was just experimenting using separate antennas yagi for repeater receive and UVS200 for TX, no major difference, my radio check is about the same. will try to key it up mobile after this storm.

 

[kayn1n32008]

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To give you an idea of what a tall tower will give you:

300' tower with a 4bay Sinclair folded dipole array (about 6Dbd gain), fed with approx 375' of 7/8" heliax attached to a UHF ham repeater outputting 12.5w BEFORE the resoc duplexer, nets a workable radius in excess of 80Km. This repeater is on the Alberta prairies and because it is flat, there is little picket fencing even at the fringe of coverage, I have used this repeater right down to S-0 receive signal strength using a 5/8over5/8 wave Larsen NMO2/70 hole mounted on the roof of my work thruck.

Power is not the great equalizer. height, feed line and antenna makes MCH more of a difference.

I have never understood why folks feel they need 100+ watt repeaters and 100watt mobiles, it truly makes very little difference compared to quality gear at the repeater site

 

[Logan005]

yep, I won't ever be at 300' I wish. and I do understand that after height, antenna and feed line are far more important than power output. if a repeater can not receive a signal it can not repeat it. Thank You Kayn1n32008

 

[mmckenna]

so you use separate TX and RX antennas in general?

It's an 800MHz trunked system. They have a 45MHz offset between TX and RX, so using separate antennas with minor vertical separation is easily done. Having to use a transmit combiner and a receive multicoupler makes it slightly awkward to use duplexors to combine into one antenna. With the 45MHz separation, the desense on the RX isn't an issue.

 

[mmckenna]

Unless I'm wrong, 50 watts ERP is the max you can run using GMRS. Your answer is going to be to figure the combination that will give you as close to 50 watts ERP at the antenna as possible.
50 watts ERP is a decent amount of power. What you really need to do to make this work is to get your antenna as high as possible.

For GMRS it's 50 watts TPO. ERP is unlimited, so antenna gain isn't an issue. However, you are correct, 50 watts is not bad at all. I run a couple of 100 watt VHF fire and PD systems and they are more than enough. 50 watts from a mobile is almost always sufficient for VHF and UHF also. Unless you do a whole lot of simplex, more power really isn't that beneficial.

 

[dksac2]

As to antenna seperation, I'm not sure of the number of feet, but using vertical seperation allows the antennas to be much closer, horizontal can be hundreds of feet at some frequencies while vertical seperation is far, far less.
The ARRL antenna book is a great source for this kind of information as is the search feature on the ARRL web site, you might try those.
When possible, a duplexer is a far better choice. Sometimes the cheap one's on E Bay ($100.00) work OK if set up right and at low power. Anything other than low power, you will be looking at used ones starting at $600.00 to get the seperation that you need.
I think the limit on the cheap one's is somewhere around 10 watts. Having them set up correctly helps. People mostly use these when making repeaters from handheld radios. Just wanted to mention the cheap one's as they might be a waste of money.

Try www.repeater-builder.com and www.hamrepeater.org There may be some good info there. www.trueladderline.com has info on using ladder line for less DB loss. www.smeter.net also has all kinds of great info on feeding antennas.

John

 

[Logan005]

It's an 800MHz trunked system. They have a 45MHz offset between TX and RX, so using separate antennas with minor vertical separation is easily done. Having to use a transmit combiner and a receive multicoupler makes it slightly awkward to use duplexors to combine into one antenna. With the 45MHz separation, the desense on the RX isn't an issue.

Thanks for the "Flat top" hair cut.

 

[Logan005]

As to antenna seperation, I'm not sure of the number of feet, but using vertical seperation allows the antennas to be much closer, horizontal can be hundreds of feet at some frequencies while vertical seperation is far, far less.
The ARRL antenna book is a great source for this kind of information as is the search feature on the ARRL web site, you might try those.
When possible, a duplexer is a far better choice. Sometimes the cheap one's on E Bay ($100.00) work OK if set up right and at low power. Anything other than low power, you will be looking at used ones starting at $600.00 to get the seperation that you need.
I think the limit on the cheap one's is somewhere around 10 watts. Having them set up correctly helps. People mostly use these when making repeaters from handheld radios. Just wanted to mention the cheap one's as they might be a waste of money.

John

Very good, I have a Blonder tongue BTY horizontal yagi 14.8db, I plan to use to feed my scanners. and an Andrew vertical/horizontal yagi 7.2db that can be used to TX and or RX for repeater or my base operations on that band. is there any rule on spacing of vertical and or horizontal yagi's? most of the 99.00 Cheap Chinese duplexers on e-bay claim 20 to 50 watt's? I am looking at several professional cavity duplexers, 299 to 500.00, but will be patient till the right deal comes along. both duplexers i currently use were made in NJ, one RFS and the other cellwave. looks like same company. I think they are considered portable duplexers.

with regard to verticals, I am thinking a 3 foot cross beam at the top of the tower with antennas mounted to each end?

 

[dksac2]

Check with the guys at DX Engineering, they seem to be the best at answering such questions.

Also, if one antenna is vertically polerized and the other horizontally polerized, they hardly interfear with each other at all on the same pole.
5 to 8 feet at the most if one is horizontal and the one on top vertical. It's just when both have the same polerzation that they need more distance between the two.

I'm putting a Par 6 meter horizontal right under a VHF/UHF vertical and the guys at Par said in such a case, there is almost zero interaction with just a little seperation.

John

 

[jeatock]

Grounding. Grounding. Grounding.

Also, did I mention Grounding???

Remember that you are building a lightning rod.

Per the R56 'Bible'-
Ground the top of the feedline coax to the tower. (Buy the cable manufacturer's specified grounding acccessory.)
Coax to tower at least every 60'.
Ground the coax at the bottom just before it turns away from the tower.
Terminate the feedline coax inside on a Polyphaser attached to a ground bus.
Ground the radios to the ground bus.
#4 copper between the ground bus and the tower.
#4 copper between the tower and your electrical entrance.
One foot of bare copper in the ground for every foot of antenna tower above the ground.

Two issues:

Lightning (Minimum- new radios, Maximum- new house after the fire).

Static bleed-off. I've found that a good part of noise problems go away when grounds are corrected.

A final note: Use Plastic conduit. I have had issues with coax resonating weirdness inside metalic pipe.

 

[dksac2]

I've read that with the type of grounding you are describing (single point) and a lot of it, that you really don't need to ground your equipment, that the final ground should be at the entrence of the coax to the house.
Either way, a direct lightning hit will most of the time fry your equipment unless you really spend a lot of money and time designing a proper grounding system.
I've gone to just grounding to the panel where the coax comes in and putting caps over the ends of the connectors and disconnecting all coax, phone line, ect as well as unplugging all of my equipment when it even looks like there could be a storm within 100 miles. I am grounded at the base of the tower (tower and coax), have a grounding panel outside with polyphasers and ground at the panel also. I must have at least 8 grounding rods, all to a single point which is the ground for the electrical mains using #6 wire. The phone and Sat TV are also grounded to that one point also. My shack is right next to the power mains so my grn runs are very short.
There is much more to grounding them meets the eye. The only people I know who have taken direct hits with no damage have spent thousands of dollars on their grounding system and they are all quite extensive.

John

So far no hits, only time will tell.

 

[Logan005]

I also shut down and disconnect much of my equipment during lighting, that is if i am home. back 20 years ago, I ran a multi line dial up internet and a multi line voice mail system, we had a strike come in thru a single phone line, travel across our network and do several thousand dollars of damage in a split second. I have had a mast up wherever I have lived and never had a strike come in on any TV, Radio or wifi feedline, that I was aware of. although I have replaced a few wifi routers. I'm grounded, probably not adequately, however i am of the mind set that I do not want to attract lighting either.

 

[Logan005]

I was wondering about that. Thanks for the recommendation, Thank you Jeatock

 

[dksac2]

Grounding is just one of those tough things. You do the best you can and pray you don't get a direct hit. In the mean time, it gets rid of static on the line from wind and other things.

Let us know how your project progresses.

My Best, John

 

[Logan005]

well I am just planning the tower at this point. with construction going on at the new house. Code enforcement is there everyday. when i do install it, I plan to leave it in it's retracted position with a regular TV antenna on it for some time so as to keep the neighbor on that side of my property from complaining, I also plan to plant two 20' "false ashoka" trees on the neighbor and street sides of the tower to conceal it. False Ashoka's are tall skinny trees I encountered many years ago in Key West. I remember thinking they would be great for concealing radio towers and mast's.