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Great range, horrible bleed. I need help.

 
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Great range, horrible bleed. I need help.
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hookahradio
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Post Great range, horrible bleed. I need help. Reply with quote
When I first started setting up my equipment I used a shitty radio shack discone antenna untuned with a 2:1+ swr and got a 5 mile radius with my 20 watt transmitter. I moved on to an even shittier radio shack yagi style antenna used for fm recievers and used a 75 to 300 ohm transformer, with I'm sure an even worse swr and got a 7.5 mile radius. When I finally decided that I wanted a real, tuned antenna, and didn't want to have a large fan on my transmitter 24/7 to keep it from nuking, I built a 1/4 wave ground plane. Here is the problem - With all those shitty antennas I tried I never had any noticeable bleed to adjacent stations. With my tuned gp, that has an swr of almost 1:1, I'm getting a 10-20 mile radius which absolutely rocks, but I'm all over the dial at full power. Once you get about 1-2 blocks from the transmitter it gets better, but doesn't improve much for about a 1/8 mile. Within 1 block forget any radio reception of any sort except for my station and 1 close local. At about 1/2 mile away adjacent stations come back but with bleed from me even at up to 5 miles away, though very little. I need to know if this is normal, and if not, what to do about it. Cheap tips are always appreciated. I am using a 20 watt transmitter located in the same room as the equipment about 4 feet away, hooked to 50 feet of RG-8 cable running to the roof of an apartment building at a heighth of about 40-50 feet. The gp is mounted to a pvc pipe mast, which is connected to an old tv antenna mast. The ground radials of the gp sit about 1-2 feet above the old uhf tv antenna which is not hooked up. Total height above ground is probably close to 65 feet. The GP was constructed per the instructions on the pcs website. So far I am not using compression or EQ. I have noticed that bass tends to distort the signal occassionaly but at this point I am just trying to get all the basic equipment set up. The sound quality is absolutely amazing with no static or pops up to 6-7 miles away(with the exception of when there's heavy bass). If you've taken the time to read this, thanks, let me know what you think.
Wed Sep 01, 2004 10:25 pm View user's profile Send private message
pcs
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Post Reply with quote
Its normal.

As I've written before, a typical radio receiver is far from perfect.
As the signal gets stronger they start to respond to all kinds of
signals they aren't supposed to respond to.

Your new antenna is ok, you have thus improved your signal strength
in the neighborhood and all the receivers are coping with large signal.

You can try to move your antenna higher and use 5/8 antenna which radiates more
towards the horizont, possibly affecting nearby receivers a little bit less.

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Wed Sep 01, 2004 10:47 pm View user's profile Send private message Visit poster's website
hookahradio
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Post Thanks Mark. One more question - Reply with quote
Will filters help with this problem? And, I'm assuming that before with the other antennas I wasn't causing as much interference because the antennas were pushing most of my output back, hence the high swr's with those. Correct me if I'm wrong. Thanks again!
Thu Sep 02, 2004 2:51 am View user's profile Send private message
Sir Nigel
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Post Reply with quote
Even with proper filtering, you'll still get a good share of interference. So I don't think it's really necessary.

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Thu Sep 02, 2004 3:17 am View user's profile Send private message Visit poster's website
pcs
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Post Reply with quote
Exactly.

I have explained this in detail in frequently asked questions,
which of course nobody ever bothers to read.

http://www.pcs-electronics.com/en/guide.php?sub=QandA#INTERFERENCE

Q: If I use filters I can put my antenna right next to my neighbor's TV antenna without any problems right?

A: Wrong! The low pass filters only attenuate harmonics. If harmonics are not the cause of your problem (they almost never are - our exciters are very clean!) removing them won't help. What causes 99% of all radio interference problems? YOUR FUNDAMENTAL SIGNAL!!! A high power fundamental signal in CLOSE PROXIMITY to ANY type of receiving equipment (TV, radio, telephone, PA system etc.) will blow right past any tuner or filtering on this equipment and enter the amplifier stage along with the intended signal where it will cause interference. This type of interference is called "fundamental overload". All the harmonic filters in the world won't help in this very common situation. What will help? Increase the standoff distance (vertical, horizontal or both) between your antenna and what you are interfering with. This is one of the many reasons high power FM radio station antennas are located on high towers. A 100 KW radio station with a 20' antenna would cause a lot of RFI even though the harmonic levels meet FCC requirements.

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Marko - PCS Electronics
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Turn your PC into a FM radio station!
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Thu Sep 02, 2004 12:02 pm View user's profile Send private message Visit poster's website
Sir Nigel
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Post Reply with quote
Hey I read it! But the average person doesn't read them, which I guess I'm not (an average person).

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Thu Sep 02, 2004 11:57 pm View user's profile Send private message Visit poster's website
pcs
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Post Reply with quote
I guess.

Haven't seen Norm around lately

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Marko - PCS Electronics
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Turn your PC into a FM radio station!
http://www.pcs-electronics.com
fax +386 4 2316 128
Fri Sep 03, 2004 2:54 am View user's profile Send private message Visit poster's website
Sir Nigel
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Post Reply with quote
Yeah, and things have felt normal here.

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Fri Sep 03, 2004 3:52 am View user's profile Send private message Visit poster's website
hookahradio
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Post Reply with quote
I read most of the posts, including that one. And I'm not as ignorant as to expect to place any rf equipment next to my neighbors antenna and not expect some repurcussions... I was wondering if somehow harmonics were being created by the antenna. Especially seeing as how I didn't have this problem before. Which is why I asked if the problem is because I'm putting out the full wattage now seeing as how I wasn't capable of doing that before due to poor tuning. My antenna is not perfect, although the swr is very low.
Fri Sep 03, 2004 5:28 am View user's profile Send private message
pcs
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Post Reply with quote
Nobody thinks you're ignorant, my friend.

It was just my general rant about people not reading frequently
asked questions. I get hundreds of emails daily with questions
which are in most cases answered in the FAQ, but they just don't take
time to read it.

It is, however, possible for an antenna to generate harmonics. It is
very unlikely and rare, but a loose connection of two metals
can act as rectifier. And rectifiers can be multipliers/mixers.
This is just a curiosity, I am certain that this is not your problem.

Good luck with your problem. Try to put your antenna higher and look
for a spot on the dial that has some 300KHz on each side empty.
That's what the big stations try to do also.

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Best regards,
Marko - PCS Electronics
--------------------------------------------------------
Turn your PC into a FM radio station!
http://www.pcs-electronics.com
fax +386 4 2316 128
Fri Sep 03, 2004 10:28 am View user's profile Send private message Visit poster's website
marek
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Post Reply with quote
I normally use "fundamental overload" to pin point a radio station's antennas if there are more than one possible broadcast antenna within let's say 100 m. In one case there was one GSM tower with 2-3 possible broadcast antennas and then approx 50 meters from there one possible broadcast antenna was on a roof. The radio station was transmitting from the latter and this could be easily concluded thanks to the "fundamental overload". In an other case there was one GSM tower on one side of the road and one communication tower on the other side and also there it was possible to see which one of them who actually housed the broadcast antenna.
The point in what I say is that as well as I can find those antennas anyone else can find our antennas with some help of "fundamental overload". They first pin point you to be within an area of let's say 100 m and then they can pin point you to more or less 10 m with the "fundamental overload". Easy as pie.
Fri Sep 17, 2004 8:31 am View user's profile Send private message ICQ Number
Vegas
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Post Reply with quote
I can tell you just what is going on.
You now have a much more efficient antenna as far as a LOW SWR goes and getting more power out.
Because of this your signal is stronger and your creating what is called a BLANKET.....an area of RF that tends to mute out other stations in your car radio until you get farther away.
This is why you have commercial FM stations say their transmitters are in one location and the station may even be in another town.
I can't run more then 20 watts MAX unless I use a directional antenna and point it where I want the power because a beam will still fire off RF at the rear.
When I called FCC they told me that the first thing they have to do is check for blanket coverage area because you can mute out your neighbors station.
You can try different antennas to see if you can get a lower TOA Take off angle.
Then you can reduce power and still reach out.
A J pole works well and you can make one from copper pipe or even 300 ohm twin lead.
Also you should use type # 43 beads on the coax right at the feed point because that will keep RF from radiating down the coax.
Winding 5-6 turns of coax appx 4" in diameter will also work
Remember FM is wide and also appx 50% efficient (or maybe better due to modern technology but when you go over 20-25 watts you need to start thinking about RF and keeping it at the antenna.
If your not bugging any neighbors then make the best antenna you can and forget about the bleeding because where I live even commercial stations conflict and one even gets into my ham gear.
Hope this helps some.
GL
Vegas/

Sat Sep 18, 2004 5:45 pm View user's profile Send private message Visit poster's website
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