let's talk antennas

[k0ua]

Most of the time 88 to 108 Mhz signals go right thru the ionosphere like a bullet thru a spiderweb. HF (3 to 30 Mhz) can and do bounce off of (the term is refract) from the ionosphere, but in general VHF (30 to 300 Mhz) signals go right thru it and on to outer space and on and on. Yes there can be sporadic E cloud refraction, yes there can be reflections from thermal layers in the atmosphere, yes there is meteor scatter, yes there is tropospheric ducting, yes there can be aircraft scatter, BUT in general VHF signals radiate up and out.

If you think about this a little bit, this is why we don't use HF or MF signals to try to communicate to space craft. We use VHF and UHF and SHF signals to communicate with spacecraft as they will leave our earth and travel beyond to where spacecraft are located, whether that be in Low Earth Orbit, or further into deep space..

So, in general you point an FM Yagi or Co-linear or any VHF array at the horizon (plus or minus 10 degrees of elevation) and on the azimuth of the station you wish to receive, NOT towards the sky. Unless the station you wish to receive is actually in the sky!

 

[k0ua]

For those that have a burning desire to know more about Radio wave propagation, I can start another thread, or point you to some resources. You can spend a lifetime learning just about this one subject, and still not know it all, as it is not all knowable.

 

[mikehaugen]

For those that have a burning desire to know more about Radio wave propagation, I can start another thread, or point you to some resources. You can spend a lifetime learning just about this one subject, and still not know it all, as it is not all knowable.

I normally do like researching new things to learn, but I tried this a little and like you said it was overwhelming really fast. That's why I decided to just post the questions here. thanks

 

[Coyote machine]

Update: new data has arrived. Keep the antenna pointed to Chi town.

 

[k0ua]

Update: new data has arrived. Keep the antenna pointed to Chi town.

That would be your best bet.

 

[locknut]

The lower VHF antenna is the CM Crossfire 3610 as suspected.It has good FM gain and will pick up all the Chicago stations clearly unless it's corroded badly everywhere,missing elements,etc.

Channel Master Model 3610 VHF TV-FM Antenna

It appears to not have a built in balun so you'll need to hook a new one on the antenna terminals,then run coax to your tuner(s).

The outdoor balun transformer on this page from warrenelectronics;

Splitters, F Connectors & Ground Blocks from Warren Electronics

Also if you run new coax down the tower,use waterproof connectors.Nothing kills a signal quicker than moisture in the coax.

 

[mikehaugen]

alright, so it's been a few months and I thought I'd give anyone interested an update. After running the coax, there was a big improvement to the reception of more local stations. I have not been overly impressed however at the reception of some more distant stations. Since the weather is somewhat breaking around here, I decided to investigate the box on the tower. It says "galaxy 3" on it. I have done a little research on it, and I guess it's a uhf/vhf preamplifier, and should have a powered amplifier somewhere. I have no idea where that is, I'm not sure that it exists. Also interesting is that while it does not specifically state that it has an fm trap, it states

Note: FM response is reduced to maintain distortion free
TV reception in the presence of strong FM signals. Preamp
will pass FM adequately in stronger signal areas, but is not
intended for critical weak signal FM preamplification.

So, without the amplifier that is supposed to mate with this, I assume I should replace it with something intended for fm reception? Any suggestions? I have no intent in the near future to use the antenna for uhf/vhf or any other kind of tv signal. I may look around a little more to see if I can find the amplifier.

Also, the little research that I have done indicates to me that I should have used rg58 cable, I will have to go double check but I think it may have been rg6. Is that a big deal?

Thanks everyone for the assistance so far.

here are 2 link I found that has a little info on the pre-amp.

http://www.bzbexpress.com/pdf/BlonderTongue/GalaxyIII_UserMan_651128300M.pdf
http://www.blondertongue.com/UserFiles/file/documents/specs/Galaxy_Spec.pdf

 

[Daver1963]

A little explanation:
RG58 is 50 ohm cable.
RG6 is 75 ohm cable.
Television (these days) operate on 75 ohm cable and that is what you'll get the best reception with. Back in olden days TVs had inputs for 75 & 300 ohm with the 75 being where the VHF antenna connected and 300 being where the UHF antenna connected.
If your FM receiver has a 300 ohm input I would suggest abandoning the 75 ohm cable and replacing it with 300 ohm twin lead from the antenna straight to the receiver. You might find out that you don't even need an amplifier. I have found that a straight unbroken piece of wire sometimes is the answer. However, if you do need an amplifier it can always be added later.
Blondertongue is good equipment. A few years ago I set up the head-end for a video distribution service and 99% of the equipment was made by them. It is very reliable stuff.

 

[Daver1963]

300 ohm twin lead.
Amazon.com: Radio Shack 100-Ft. 300-Ohm Flat Twin-Lead Cable: Computers & Accessories

 

[k0ua]

Keep in mind for a mast mounted preamp to work it must have a source of power inside feeding the transmission line. Since you don't know where this is, or even if it still exists, and your research indicates this preamp is actually an attenuater in the FM band, I would remove it.