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Old March 11th 14, 02:42 AM
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Default Antenna question

My question is not really ham related but I'm hoping someone can offer some advice on my problem or if not, maybe you can direct me to a more appropriate group/forum.

I'm troubleshooting a bad reception issue. I bought a Magnum Dynalab ST 2 FM antenna, put it up on the tower in the back yard connected it to a NAD 7220 PE receiver via RG 59 cable and a 75 to 300 Ohm transformer and all I hear is what I can best describe as a howl.
The strange thing is I accidentally discovered that with the cable's terminal wires are near, but not connected to the receiver I get a strong, clear signal from a local FM transmitter but the signal broadcasted by a Whole House FM transmitter connected to a source in the house produces very bad reception in the garage woodshop less than 100 feet away. The transmitter should be good for nearly 1/4 mile.
I'm sure it's not an issue with the transmitter as the FM section on a portable MP3 player picks up the signal fine all over the back yard.

Unfortunatley I don't have another FM receiver to experiment with and I'm starting to wonder if my receiver need servicing.
I'd be very appreciative if anyone could give me some direction.

Thanks for reading.

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Old March 12th 14, 01:59 PM
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Originally Posted by kneedeep View Post
My question is not really ham related but I'm hoping someone can offer some advice on my problem or if not, maybe you can direct me to a more appropriate group/forum.

I'm troubleshooting a bad reception issue. I bought a Magnum Dynalab ST 2 FM antenna, put it up on the tower in the back yard connected it to a NAD 7220 PE receiver via RG 59 cable and a 75 to 300 Ohm transformer and all I hear is what I can best describe as a howl.
The strange thing is I accidentally discovered that with the cable's terminal wires are near, but not connected to the receiver I get a strong, clear signal from a local FM transmitter but the signal broadcasted by a Whole House FM transmitter connected to a source in the house produces very bad reception in the garage woodshop less than 100 feet away. The transmitter should be good for nearly 1/4 mile.
I'm sure it's not an issue with the transmitter as the FM section on a portable MP3 player picks up the signal fine all over the back yard.

Unfortunatley I don't have another FM receiver to experiment with and I'm starting to wonder if my receiver need servicing.
I'd be very appreciative if anyone could give me some direction.

Thanks for reading.
SINCE my crystal ball is broken, there is no way for me to look through the cosmos to see what it is that you are experiencing.
Sounds to me a lot like overload.

Go to FMfool.com and look to see what else is in the neighborhood and it's signal level.

My guess is that you cannot use a whole house amplifier and a receiving antenna for broadcast FM radio in the same general vicinity. You need to choose - either or, or shut the whole house transmitter off when you wish to receive broadcast FM stations...
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Last edited by Channel Jumper : March 12th 14 at 02:02 PM
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Old March 13th 14, 11:42 AM
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Originally Posted by Channel Jumper View Post

Go to FMfool.com and look to see what else is in the neighborhood and it's signal level.

My guess is that you cannot use a whole house amplifier and a receiving antenna for broadcast FM radio in the same general vicinity. You need to choose - either or, or shut the whole house transmitter off when you wish to receive broadcast FM stations...
Thanks for the site, it will be useful.

I have no problem receiving broadcasts from FM station that are within a reasonable distance and having the transmitter on or off makes no difference.
It is set to transmit a signal at 88.1 MHz - there's no station within my listening area broadcasting on or near that frequency.

Since I posted the question I found that mounting the antenna on the tower - not on a mast but on the actual tower - effectively detunes the antenna.
So I suppose the solution is to find a better mounting spot away from the metal of the tower - or get it higher and mount it above the yagi that's on the mast now but that presents a problem with the cable length being overly long.

Thanks for your input and sorry to hear about your crystal ball.
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Old March 14th 14, 01:59 PM
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If you understand FM - you will realize that FM has many side bands - hence the center frequency of your whole house transmitter is 88.1 - but it has harmonics on other frequencies on either side of 88.1 - this is how FM works!

All signals reduce at the square of the distance away....

You either need to move your transmit or your receive antenna - have some sort of separation between the two or use a filter.

http://dsp.stackexchange.com/questio...d-in-am-and-fm
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Old March 17th 14, 05:59 PM
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Originally Posted by Channel Jumper View Post
If you understand FM - you will realize that FM has many side bands - hence the center frequency of your whole house transmitter is 88.1 - but it has harmonics on other frequencies on either side of 88.1 - this is how FM works!

All signals reduce at the square of the distance away....

You either need to move your transmit or your receive antenna - have some sort of separation between the two or use a filter.

http://dsp.stackexchange.com/questio...d-in-am-and-fm
Harmonics I understand but I'm not sure how it applies to my problem.
As I said I am able to get FM broadcasts available in my area and I do get a signal at 88.1 from the transmitter in the house. The nearby commercial FM stations are clear no matter if my transmitter is broadcasting or not but when I raise the antenna above the roofline - all bets are off and not all are listenable.

I can get the transmitter's signal (and commercial FM broadcasts) as long as the antenna is on the ground but they are not noiseless. As soon as I raise it, say to the peak of the garage roof, most stations I'm interested in get very noisy to completely unlistenable depending on the antenna's orientation.

Testing, I positioned it lying on the roof and oriented in several different directions. Some positions were good for one favorite station but not the other and none of the positions I tried would receive both the two favorite stations and the transmitter.

When I bought it back down to ground level I could find a spot or two that allowed reception for all frequencies, but again not clearly.

Due, I guess, to the nature of frequency modulation, at some times of the day no amount of re-positioning the antenna would allow getting a clear signal from the more distant commercial stations, only the nearest.

Moving the equipment to another area of the garage made a huge difference so I'm thinking wiring in the garage might have affected the signal path.

Sorry I don't understand what you mean by "...have some separation between the two..." they are now 50' to 75' apart, wouldn't that be sufficient? - and what sort of filter are you referring to?


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Old March 18th 14, 12:23 PM
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Frequency Modulation works on the principal of Capture Effect - where it receives the strongest signal and ignores the rest.

http://en.wikipedia.org/wiki/Capture_effect

You have to be able to look at what is in your first and second Fresnel Zone.

http://en.wikipedia.org/wiki/Fresnel_zone
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Old January 2nd 17, 06:37 AM
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Originally Posted by Channel Jumper View Post
Frequency Modulation works on the hydromax website https://www.the5x5project.com/my-hyd...review-results principal of Capture Effect - where it receives the strongest signal and ignores the rest.

http://en.wikipedia.org/wiki/Capture_effect

You have to be able to look at what is in your first and second Fresnel Zone.

http://en.wikipedia.org/wiki/Fresnel_zone
Easier said than done for a newbie.

Last edited by Towner : May 8th 17 at 04:38 PM


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