Well lets start off by gathering a bit more information. What type of antenna, the band of operation, proposed height, distance from buried water/utility pipes/wires, feed line type, power level you will be operating.
Peace!
K-ROCKS RadioOne
ZeroPointRadio
AM Stereo 1670
FM Stereo 92.1
Ok...that is a start. A full wave out of copper pipe...good choice for the element material. If it were me, I would split that full wave up into two 1/4 wave dipoles phased and stacked to double the gain.
In any case, you may run into some issues with the mounting of that full wave on the mounting structure and the separation between the mast and antenna itself...unless you mount it at the very top, in which that does not give very much mounting surface for a full wavelength copper pipe at 90.3. Some tuning/trimming may be required. Use a SWR meter full time on that to monitor.
Pound an 8 foot grounding rod into the dirt next to the mast. Attach with short piece of 6 gauge solid copper grounding wire to the base of the mast. Connect the shield braid of your coax to the same point as the 6 gauge copper wire at the base of the mast. Then at the top, connect the shield braid to the mast at the point where the base of the antenna itself mounts to the mast.
You may also want to run some 6 gauge solid copper wire from the ground rod into your shack/studio and attach that to every ground lug and connection on your racks/equipment.
You might want to consider using a J-Pole instead of that full wave, open ended copper pipe. A J-Pole will give you about 3db gain and be DC shunted...meaning the entire antenna is at DC ground potential and is FAR safer than an open ended whip. It will prevent static buildup as well as directly shunt any lightning directly to ground instead of down your center conductor of the coax with that full wave antenna.
Peace!
K-ROCKS RadioOne
ZeroPointRadio
AM Stereo 1670
FM Stereo 92.1
Post by Ozone Express Radio on Jul 27, 2011 20:56:23 GMT -6
Running FM right now, I have three ground rods driven into the ground here.
All of them are 60" in length, and are driven into the ground leaving only approximately 2 inches sticking out.
One is connected to my antenna ground via the outer shield of the coax and the antenna itself. I'm using a Comet GP.
The second is attached to all of the grounds of my equipment. Mixer, TX, power supplies, audio source, laptop and desktop (via the USB connections) tape decks, turntables, reel-to-reel, 8-track, etc.
The third is connected to the breaker box that feeds all of my equipment.
Proper grounding can't be over stressed. I've beat my head against the wall trying to chase down funky noises and other weird stuff due to poor or non-existent grounding. Don't skimp here and do it right.
I've never had an issue with grounding here oddly. I do have two 8' ground rods pounded in about 4' apart which does more than enough for the FM transmitter I use. Usually I only have noticed buzz in the audio from improper audio cable shielding, or having coax too close to audio components, usually fixed by using ferrite RF chokes along audio lines. Though the leak is low it's still enough sometimes to cause RF feedback. Once everything is positioned correctly all works well. If you notice hum it does help sometimes to reposition audio cables, coax, and even sometimes equipment.
Also beware of "ground loops" which can cause hum. This is very often the cause of hum issues which is usually resolved incorrectly by adding more grounding and not solving the initial fault.
VHF frequencies used for FM sometimes have mysterious ghost like properties where RF likes to get into places you'd least expect and usually a simple few inch cable movement or moving one piece of equipment in the transmitter room into a different place can cure a loud buzz to pure clarity.
But anyways on topic, even with the best grounding with FM it doesn't always help when running a transmitter in the same hut as the audio. It takes a lot of playing around to get everything just perfect. Sometimes using no ground can even be effective when using a few watts or less.
I know this may go against practice but I personally believe that a station should use as little grounding for FM as possible for RF and modulation to be effective and clean, but yet as much grounding as possible to prevent from lightning. What I mean by this is that in a perfect world we should need little grounding for audio issues if everything is working properly. If your SWR is low and the transmitter is at a good distance from the studio, proper RF choking in the audio chain is applied then virtually no ground should be required. If you can achieve this then you're set. THEN add the ground rods one by one to protect from natural enemies like lightning.
Now with Medium Wave AM that's a whole different beast. If something is out of whack with AM the whole damn audio chain gets RF feedback. Even when things work right sometimes I get AM into mics or odd bits of equipment that get hooked up on the fly that weren't tested prior to broadcast. Funny part about that is, even professional broadcasters and engineers have those issues, so we don't have to feel alone
The cherry on the ice cream is when you run both AM and FM broadcasts out of the same place. Lets just say it's a total pain in the ass. Not only do you have to worry about grounding on AM and cross grounding with FM, but also mixing of signals if antennas are too close causing the FM broadcast to image/mix every few MHz on the FM dial, AM getting into the FM broadcast, FM getting into the AM, and ugh you have no idea! LOL. It took me lots of sweat, anger, and hell to get such a setup working.
BTW even though this may be slightly out of the original posters question, I feel it's good information that we should all learn and know about ground loops which often more than not are the real issue with broadcasting... www.epanorama.net/documents/groundloop/
With RF it's a matter of wavelength I think? Ground cables on one piece of equipment being longer than another piece of equipment causes not only a resistance difference in the ground but also a culprit of wavelength RF interference. I have noticed this when just moving cables around which can go from buzzes in audio to clean audio. The movement of the cable changes its reception of wavelength introduction from surrounding RF from the transmitter. Thus I think (speculating...) that coiling wires or length of wires literally act as receptors of surrounding transmitter RF radiation or reflectors. Ugh I am either drunk now or I think I am on to something lol.
With RF it's a matter of wavelength I think? Ground cables on one piece of equipment being longer than another piece of equipment causes not only a resistance difference in the ground but also a culprit of wavelength RF interference. Thus I think (speculating...) that coiling wires or length of wires literally act as receptors of surrounding transmitter RF radiation or reflectors. Ugh I am either drunk now or I think I am on to something lol.
Quite correct. This is why it is best to have as straight of run of ground buss as possible. There also may be a need to have a "technical" ground, which is an isolated and separate ground rod and lead buss to the audio gear away from the transmitter systems, similar to how important it is for an isolation between a close spaced AM and FM system.
Sometimes that is not enough either, some stations have to use a "VSHSTL". Very Short Haul Studio Transmitter Link, where the studio is located in the same place as the transmitter and the only way to avoid ground loops and/or audio line RF induction problems is to wireless the audio from the studio to the transmitter.
Using 1:1 audio transformers is another effective method to eliminate ground loop and hum, and often does a pretty good job in acting as a low pass filter in of itself to block RF. Shielded 1:1 transformers are excellent for work in near field high level RF.
Enjoy that drink!
Peace!
K-ROCKS RadioOne
ZeroPointRadio
AM Stereo 1670
FM Stereo 92.1