Marantz 20b/Fm reception/ Antenna height and other questions.

[KutzlerTrans]

Hey tuner guys, and girls.
First time in the Tuner section for me.

I am about to install a rohn 23/25?G tower for my tv antenna..
I also have a pile of antenna parts saved for a future fm antenna.
As a result of having to eventually work/add or swap antennas, i am installing a pivot.

The tower is around 35' tall. I plan to add at least 10ft, but as of now only have a cut in half old CM antenna, so wind resistance is nothing. I would like to put up a parabolic 7" CMaster if i could find one.

As far as making an FM antenna, i would stick to something around 12' length do to the dual frame CM quantum 1160 antenna i am going to base it on.
That is material for a whole nuther thread
These questions sound like i am talking more tv than FM but i just want to make the connection.
Here is one question.
In theory since tv is UHF, and based on line of sight, i should be able to pick up a signal out to about 185 miles as long as the transmtter is around 35ft up.


Questions,
1)
So, am guessing FM is more like VHF but also confined to the curve of the earth, which for Uhf every ten ft of height, would increase coverage to 25 miles?
Or, is there an issue with ground interference that explains why my tv only gets out to 80 miles.
It appears to me that the only way for the
{D = 1.33 x (2x height of my antenna) + 1.33 x ( 2x height of transmitter) } formula would work, is if there was a fudge factor of 40 ft.
Not knowing transmiter tower height does not help , as i have no clue.
Question 2)
So, is FM different than Uhf when it comes to this calculation?

I bought a marantz 20b that i am going to restore electronically and send to my friend Rbuckner for an allignment. He doesn,'t know this yet so i'm crossing my fingers until he gets back on ak and cks his messages.

I have heard of a guy called Punkerx that is a master at massaging every ounce out of these 20b's

Mr PunkerX, if your out there and Randy declines or is too busy, could you help me?
I restore Marantz receivers but know my limits as far as Fm goes.

I'm sure i'll get to know you guys when i tear into this restoration.
Question 3)
What is the optimum height for an Fm antenna before cable length takes its toal on the signal?
Question 4)
When i do eventualy add the fm antenna , does placing it below the tv antenna comprimise the signal as i think it would?
Question 5)
How many ft should they be apart?
Question #5)
Lightning!
I have the welder for permanantly welding the braided copper cable to both the tower and ground rod.
How do i best protect the tuner from getting hit?


Thanks for your advice, John

 

[RxDx]

fmfool.com and tvfool.com will give you some idea of geography affecting your reception.
It will also let you plug in different antenna height values.

Disconnecting the lead-in during bad weather is the best protection.

 

[Punker X]

Yes I can align a Marantz 20B.

Agree, with the websites given. Check out the Out Door Antenna Performance sticky at the top of the forum.

Also suggest disconnecting is the best protection.

 

[rcs16]

Hi John,

Just to let you know it does not have to be expensive. I am using what came with the house I bought in 1990, it is a standard deep fringe LPA TV antenna, on a 40ft tower with a amp up top. I had the local TV guy climb the tower a couple of years ago to install a new channel master rotor. It still has the old 300 ohm balanced TL which is in great shape, no cracks in it. I have a antenna discharge unit in the house. The amp terminator has 2-300 ohm o/ps, one I use a 300/75 balun,RG-6/U to a tuner in the basement, the other goes to a distribution amp for signals to other tuners in the house.
It works great.
I pick up stations up to 75-100 miles away. You really need a rotor. Sometimes, usually at night, I get some mixer over loads on some tuners on certain stations. The FM band is packed in my area, with many strong adjacent carriers.
There should still be a few old TV towers around that people do not want and you could probably get for free if you ask them. People leave them up since they do not want to pay for someone to remove them. Still a PITA to deal with, either putting them up or taking them down.

Question 3)
What is the optimum height for an Fm antenna before cable length takes its toal on the signal?

It is a compromise, height gets you more signal strength, TL/cable lengths attenuate more signal. If you use a amp at the top of the mast, you compensate for TL loss. FYI 300 balanced has lower attn than most RG-6/U's do, but are more susceptible to interference.

Question 4)
When i do eventually add the fm antenna , does placing it below the tv antenna compromise the signal as i think it would?

I do not think so unless they are too close.
Take my advise and use a LPA deep fringe, all in one solution.
Adding more antennas creates more wind load, might have to secure the tower with guy wires.

Question 5)
How many ft should they be apart?

That I am not sure of, I guess more than a 1/4 wavelength

Question #5)
Lightning!
I have the welder for permanantly welding the braided copper cable to both the tower and ground rod.
How do i best protect the tuner from getting hit?

grounding the tower does nothing if the antenna takes a direct hit. As said above disconnect the feed is the safest way.
If you have many taller tress in the vicinity you are better off. If you do not you are a target. Lightning takes the shortest path.

Good luck

 

[I LIKE MUSIC]

John, you will get a lot of advice on what to use for an FM broadcast band antenna. Remember that it is all about the signal at your antenna and not someone else's antenna.

Regardless of the type, LPA, LPDA and so on, most TV antennas do not perform as well as a purpose built FM broadcast band antennas for FM reception.

I am not sure how you came up with 185 miles with your proposed antenna installation and a TV transmitter antenna height of 35 ft.



I have manually run the numbers and this is a fairly accurate ballpark calculator. The numbers are what you indicated in your post.

Some people are able to receive stations at distances in excess of what this calculator would predict. Again it is about location and what is between the transmitter and receiver. There may be structures, natural and or man made that cause reflections, refractions and or what are called knife edge diffractions.

BTW, here is a second calculator just to double check the numbers of the first calculator.





Back to the antenna. A single TV antenna may provide you with the needed reception capability for the FM broadcast band, but no one can predict and recommend a specific antenna without knowing the amount and quality of the signal that your antenna will see.

In comparing the FM broadcast band to the UHF TV band the line of sight path loss in greater for the UHF TV frequencies.

Just as an example, given RF line of sight, at a distance of 50 miles the path loss for the FM signal is about 110 dB and for the UHF TV frequencies about 125 dB. The larger the number, the less signal you will have to work with.

The first place to start for information about grounding your antenna installation is the NEC. Depending on what you want to do additional steps such as the addition of gas discharge devices and ground rod arrays to lower the impedance to ground that the lightning discharge energy will see. This may help with close cloud to ground strikes and cloud to cloud discharges.

 

[KutzlerTrans]

Thanks for the advice!
I used an online calculator for tv distance. Not sure were i found it but it makes sense why i only get 70m if my calculation info is wrong.

Grounding the tower is to prevent flashover to the metal on the house. I know it sounds crazy but i am putting lightning rods on my house and plan to be grounding the crap out of them. I am going to drive the rods down about twelve ft (to ground water ) and plan to run 2 or 3 rods per down wire . 2 down wires per lightning rod.
I am restoring the house back to its 1880's look and the lightning rods look too cool on it.

As a volunteer fireman, i usually have to put out one lightning struck house every few years. Most of the time it hits a near by tree and travels into the house through buried wires and blows out the fusebox, burning the house down.

I am looking into putting in the rubber clad gas piping with a check valve for cutting the gas off like a proportionary valve.

I believe i have everything to put the antenna up around 45ft now including a pivot base i found yesterday. I'm going to have to dump almost a yard of cement into the hole after figure out the best way to bolt the pivot into the cement block.
I have to come up with some tough long galvanized bolts from a substation or something.
Might dump a few big I Beams into the hole and weld and bolt the plate down. Then paint it again with cold galvanizing paint.

TV fool is a great resource for info.
I will have a long route for my antenna wire, so i may have to experiment a bit. What sucks is we just resided our 140 year old house with cement board siding and i could have run the antenna wires in the walls of a couple of rooms if i was thinking ahead.

The distance of any majors fm station is the average of 50-70 miles. Were rural and ony have one stop light in our whole county.
A fair amount of fm reception is coming from due north and south.
The average distance is 60 miles.
The rx dbm starts around -56. ( around 15 stations twix -56 -/ -69
Centers around -75 ( around 15 stations in the -70's)
Ends around -87 (around 20 stations in the -80s)

Any ideas or plans about how to build an antenna that beams 180° & 360° ?