let's talk antennas

[mikehaugen]

Well I know there are a lot of tou ham operators and others out there that know about radio waves and such. I have a tv antenna that isn't being used anymore because of the dish. I would like to utilize it for fm reception. There is a receiver in the house and in the garage that need better reception.

For whatever reason there are 2 different types of antennas up there (see pic) pointed east. I live about 80-90 miles west of Chicago and about 40 miles south of Rockford, both of which transmit. I would prefer Chicago, and that is where the antenna is pointed it seems. The two antennas feed into some kind of box, which then has a coaxial cable running down the tower. I can split that cable and run coax to both places using rg6. The question I have is how do I connect it? The receiver in garage has both a 75 and 300 ohm input. I see 300 ohm adapters, but do I really need that since I have the 300 ohm input? I don't see any just straight coax adapters to wire to the screw terminals, so how do I wire into those unless I use the transformer?

Also, what do you suggest with the antennas? Keep using them both, or just one? Airwave transmission is quite confusing and what I am trying to do seems pretty simple. Thanks for any suggestions.

 

[Jimbrown]

The two antennas are top UHF bottom VHF. The box is a combiner. Leave all that alone.

Put a 75 ohm to 300 ohm transformer on the end of the coax and connect to the 300 ohm terminals on your radio.

Receivers are not near as picky as transmitters it should work very well.

The FM radio band fits in approxametely the middle of the VHF TV band.

You can buy the transformer in any home store, wallmart, or hardware store.

Indoor Matching Transformer - UHF/VHF/FM | ShowMeCables.com

 

[buickanddeere]

There is probably a FM trap in there which reduces FM interference to TV signals in the CH2-CH6 area in particular. FM radio is in the spectrum between TV CH6 and Ch7. I would retain the ability to receive TV from the antenna.

 

[mikehaugen]

Thanks everyone for the replies. I will run the coax and use the transformer for the reciever and see what happens. If everything works out I will be happy. If I need to get into amplifiers or anything I will probably be back on here asking. I am pretty confident because I can usually get reception in my car up until about a mile or two from my house.

Okay, maybe I do have another question. The inside of the garage is lined with steel panels on all walls and ceiling. I believe this is why I have a hard time getting reception in there now, even with some of the very close (under 20 miles) small local stations. I think the metal shouldn't be a problem as I am pulling the signal from an outside antenna, but thought I would bring it up in case there are any other considerations I need to be aware of with it.

 

[Pete Judd]

The metal building is blocking your FM. Run coax from your old outside tv antenna, to your radio, and you should be good to go.

 

[mikehaugen]

Okay, so an update if anyone was wondering... I got the coax ran last week and it definitely helped a lot. I can probably get acceptable reception on about a dozen stations, versus the 1 from before. They are all local stations (like within 40 miles). I am still confident I can get Chicago stations though. My thinking is that I can get them in my car until about a mile or two from home, also since the previous owner had the antenna pointed that way I assume he was getting tv from there. I will still probably go up there and check out that box to see if has a trap, though that may wait until next spring.

I am happy with the stations I have though. It's funny how out here I get about six country stations, out of about 12. Chicago and suburbs have 2, out of probably 20 or more. I like country music, but with all that crap mixed in now it's nice to have another station to switch to.

Thanks again for the help guys.

 

[locknut]

You should get much better reception than the car radio.The ants on the tower are being fed into a preamp which I assume is not being fed any power from a transformer.Won't get much of anything from the ants without the transformer.If you go up the tower,take some new coax and a new outdoor balun transformer and hook it to the bottom ant.It looks like a channel master crossfire and may have a builtin balun.If so,hook the new coax up to that.A dedicated FM antenna will work better.

 

[locknut]

The tower setup is UHF/VHF seperates with a dual input preamp.With no transformer to that preamp not much of anything will come through.you need to run coax directly to the lower VHF antenna without a preamp for best FM reception.Can't see the pic well enough but looks like a CM crossfire and might have a built in 300/75 ohm balun that you hook the coax directly to.If not,install a new outdoor balun on the terminals then coax on down.For best reception a dedicated FM antenna would be ideal.Never use a preamp for FM.

 

[Coyote machine]

You'll get better reception if the antenna points toward the sky instead of toward Chi town.

 

[mikehaugen]

You'll get better reception if the antenna points toward the sky instead of toward Chi town.

I wondered about that actually. Seems I remember from somewhere that radio waves bounced off the ionosphere or something. I always wondered if it had something to do with why it seems on super clear nights I get worse reception. Maybe it's my imagination though.

 

[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.