Once every few years I help out with this event in which I set up a transmitter to send an FM signal about 450 feet across an open area. I have had problems with this so I keep upgrading the transmitter power. Currently I have an (advertised) 7 Watt output Chinese FM stereo transmitter that
has digitally syntheisized frequency with digitial readout. Yes, I know this is illegal. Call it pirate radio for 10 minutes once a year. Nobody gets hurt.
Anyway, the receivers tried include small digital headset type up to full home stereo rack mount type with external antenna. I always set it up and test it a few
weeks before and everything works just fine. My transmit antenna is a home built dipole. When the event is on there are about 2000 people around, most with cell phones ON, I am sure. And the reciever is no longer working, or barely working. I try lots of blank frequency slots. Nothing is reliable.
Is it possible the cell phones are causing interference on the FM band (88 to 108 MHz.)? Any other ideas on how to fix this problem?

 

What receiver isn't working?

 

I would guess that your problem is with a bad cable or antenna. The cell phones shouldn't be bothering any receiver.

 

What receiver isn't working?

None of the receivers work much better than the others during the event.
I can get 1/2 mile range in my neighborhood, testing by driving around with my car radio on.

 

I would guess that your problem is with a bad cable or antenna. The cell phones shouldn't be bothering any receiver.

I have tried differnt antennas, each with their own cable. Some work a little better than others except during the event.

 

Do you know what a SDR dongle is? This should allow you to look at your transmitted signal........and anything that is interfering with it.

 

Do you know what a SDR dongle is? This should allow you to look at your transmitted signal........and anything that is interfering with it.

Yes, I was looking into that. Does anyone know where there is a free Windows application that turns one of these into an RF spectrum analyzer?

 

Here is a list of some of the free software available for a sdr dongle......or any sdr radio.

http://www.rtl-sdr.com/big-list-rtl-sdr-supported-software/

 

Thanks! I will order one of these Software-Defined Radio receivers. I also need to look into getting an inexpensive SWR meter
to check my antenna(s) for good efficency. Any ideas for that?

 

You probably needto look at your reciever antenna, Do you know anything about tuning an antenna? They have a gain rating too. What is your TX frequency?

 

I do have a question about their primary receiving antenna. It is a vertical whip antenna mounted up in the rafters of a wooden building.
However they have mounted it upside down with the feed line at the top. I know quite a bit about antennas but I do not know if this would have a negative effect on the reception. The frequency is 90.3 MHz.
Currently I am building a new transmitter antenna. I was using a J-pole but I am building a 1/4 wave vertical with 4 ground-plane radials to be fed with coax.

 

Make the wire the resonant freq length of the freq yo are trying to receive .This applies to both the transmitter as well a the receiver. A good antenna could make your setup illegal, as the FCC cares a lot about actual radiated power. In RF theory antennas are a huge part of it . It was my core subject in college but I get the impression you are new to the subject,as I recall you want a wire 98%of the wave length, length in this is literal.
L=c/f
Been 40 years and I am dealing with brain fog from a stroke, but I suggest you read up on antenna theory through Wikipedia or whatever.

The gauge of the wire is not important They must both be the same orientation, be it horizontal or vertical.

Hope this helps.

 

Again.....what receiver? Please clarify your setup. And the upside down whip in your rafters......is bad juju.

We can't read minds. When you say receiver....you know what you mean. We don't. When you say antenna....you know what you mean....we don't.

We can only make general comments.....from your general terms.

You say that everything works fine.....until people show up. So why do you want to check SWR or try different antennas?

Why not get a dongle and check your transmitter first? Connect your dongle to a laptop, 1000 ft away from transmitter. Now compare your signal.....with and without people.

 

Hello,

Did the J-pole antenna have the right dimensions?
Here is a calculator where you can check the dimensions:
https://m0ukd.com/calculators/slim-jim-and-j-pole-calculator/
There are also dimensions given for the slim jim antenna.

As said, the transmitter and receiver antennas must be both horizontal or vertical.
When one is horizontal and the other is vertical, an attenuation of about 30 dB will happen.

Bertus

 

I did say above, that I have quite a bit of experience with antennas. I am an EE and an amateur radio operator.
Yes, I know about antenna polarization. Yes, I did state that the primary reciever is "rack sized" FM stereo receiver.
Thanks for the J-pole calculator. Will check the dimensions.
I also know how to calculate antenna lengths. I just did not know if the upside down whip antenna is bad. I don't know
exactly why picking the signal off the top of a vertical is bad but I will insist that they reverse it.
Thanks all for the ideas.