Antenna Tuning?

[bonehead]

one thing that you can do is head over to the local ham radio shop and ask them if they know of anyone that has a SWR meter (all hams should) and would be willing to tune your antenna.You can use all the tables you want to but not many take into account the amount of metal that is being used in a caged truck.... yes it has an effect on the signal. The math formula for getting close to the correct length is ...468 divided the frequency in megahertz. That is for a half wave length antenna

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[Zambo]

Never have had good radio communications from main pit. I thought it was because of using a 50 watt radio but I have seen some posts that mention properly tuning the antenna. How do you tune the antenna?

Thanks

The antenna is important but so is the power supply. How are you powering the radio? They are designed to put out full power at 14+ volts, which is what your alternator runs at. A fully charged battery is 12.6 volts and just that little power drop decreases your power out substantially. If you are running on a battery only, it will discharge during the day and your power out will decrease rapidly and your radio will become just about worthless.

[Weatherman]

The antenna is important but so is the power supply. How are you powering the radio? They are designed to put out full power at 14+ volts, which is what your alternator runs at. A fully charged battery is 12.6 volts and just that little power drop decreases your power out substantially. If you are running on a battery only, it will discharge during the day and your power out will decrease rapidly and your radio will become just about worthless.

Good post! I have been beating this drum for many years. When ever your communications suck, start with the power supply using a volt meter at the connector to the radio under transmit conditions, engine running, and comparing the voltage at the battery. This simple test will tell you several things including; power loss due to bad and/or sulfated connections, loss due to improper guage wiring and cigar cords open a new list of challanges! Direct to the battery is always the best, both positive and negative leads. Direct to the battery most often eliminates alternator noise. When in doubt call PCI Race Radios and ask for Scott, Gerardo or Jimmy.........................................

[SoCalRally]

The antenna is important but so is the power supply. How are you powering the radio? They are designed to put out full power at 14+ volts, which is what your alternator runs at. A fully charged battery is 12.6 volts and just that little power drop decreases your power out substantially. If you are running on a battery only, it will discharge during the day and your power out will decrease rapidly and your radio will become just about worthless.

You make a valid point, but I think your statement that 'your radio will become just about worthless' is a slight over reaction. Power is proportional to voltage squared, so if e.g. over the day your radio's supply voltage drops to 12V (truck off, therefore alternator not running), your TX output power would be only (12/14) ^ 2 = ~ 73.5% of what it would be if the truck was running and the voltage was therefore 14V. A definite drop to be sure, but I wouldn't characterize it as worthless.

Also, power works on a logarithmic scale, so say you have a radio that is capable of putting out 100W, that is now only putting out 73.5W, the difference in power (and hence range) isn't as great as it might first seem i.e. you don't have 100/73.5 = 1.36 = 36% more range.

Depending on many other factors e.g. terrain, antenna type, antenna wavelength, antenna tuning, height above average terrain (HAAT), location of transmitting party & receiving party, etc., running off battery voltage without the truck running (and hence limited to ~ 73.5% of max power) might be fine some of the time.

However, in an emergency, or if you're working a pit & your team is expected in soon, or if you're right on the edge of being able to talk to another party, starting the vehicle to get an extra boost to get full power (and hence range) can be worthwhile.

Good post! I have been beating this drum for many years. When ever your communications suck, start with the power supply using a volt meter at the connector to the radio under transmit conditions, engine running, and comparing the voltage at the battery. This simple test will tell you several things including; power loss due to bad and/or sulfated connections, loss due to improper guage wiring and cigar cords open a new list of challanges! Direct to the battery is always the best, both positive and negative leads. Direct to the battery most often eliminates alternator noise. When in doubt call PCI Race Radios and ask for Scott, Gerardo or Jimmy.........................................

Bob brings up a related but slightly different issue. Using appropriately sized wiring, securely connected, and directly connected & appropriately fused near the battery will result in optimum battery supply voltage to the radio, both when the truck is running and whether it's not running.

[Zambo]

I don't believe I ever implied that terrain, elevation, antenna type etc don't count, in fact I give a detailed comm briefing to our team before the races which cover all of those things and more in pretty good detail. But power out is as big of a concern as any of those things and I made a point of mentioning it because it is a one of the most common mistakes that people make and it is easily corrected. Btw, when I said that the radio becomes almost worthless you will note that I said it was when you have run the battery down (which will happen quickly if not being charged), not when the battery is charged to 12 volts.

[SoCalRally]

I don't believe I ever implied that terrain, elevation, antenna type etc don't count, in fact I give a detailed comm briefing to our team before the races which cover all of those things and more in pretty good detail.

True, the only reason I brought those issues up is because they also affect range e.g. if someone is 3 miles away on flat land with no obstacles, and both antenna are tuned correctly, you should both be able to hear each other just fine, even if the radio supply voltage (and hence power and range) was less than the maximum possible. Now obviously the scenario I posted is close to ideal, and in practice things are likely to be worse e.g. you are on opposite sides of a hill. My point was merely that slightly less than maximum power may often be enough.

But power out is as big of a concern as any of those things and I made a point of mentioning it because it is a one of the most common mistakes that people make and it is easily corrected.

Yes, it is easily correctable (by switching the engine on & getting full alternator voltage). But is it practical or desirable for a chase truck to have its engine running for, say, a full 24 hours straight at the Baja 1000, just to get 20% more range?

Btw, when I said that the radio becomes almost worthless you will note that I said it was when you have run the battery down (which will happen quickly if not being charged), not when the battery is charged to 12 volts.

Actually in your original post (#12 above), you were comparing 12.6V vs 14V, which results in < 20% power loss, and even less loss than that when you consider practical range. However, I agree that if one, say, were to run one's battery down to 11V (pretty low, most batteries are considered flat at 10.5V), then the power loss would be closer to 40%, and indeed the voltage seen by the radio starts to become a much more significant factor. How quickly one runs one's battery down is largely a function of one's TX duty cycle vs. RX duty cycle vs. Idle duty cycle. A typical usage pattern for the Baja could be something like 5% TX, 25% RX, 70% idle. Neither idle nor squelched RX draw a lot of current, probably somewhere around 0.5-0.7A for most radios. For chase trucks with a > 60Ah battery (and sometimes double that for diesel trucks with 2 batteries), the idle & RX current draw aren't really that significant. However, if one runs a high power radio, that can draw 20A @ 100W output, then at an average of 5% TX, one is using roughly 5/100 * 20 = ~ 1Ah per hour on average. If one adds the idle & RX current back in, maybe the overall average is something like 1.5Ah per hour. If one starts off with a healthy, full charged battery, it'll take quite a while to run down a > 60Ah battery (or twice that for diesel trucks), when drawing an average of 1.5A.

So what does this all mean? Well, when communications is critical or important (e.g. emergency, team about to pit soon etc.), having the engine (and therefore the alternator) running to get maximum supply voltage to the radio may well be desirable. But the rest of the time simply running the radio off the battery, and say starting the truck for 15 mins every few hours to recharge the battery may well be sufficient.

2 last points:

1. Running at a lower radio supply voltage (assuming it's high enough that the radio stays on, of course), only affects one's TX Range. RX sensitivity & RX range is largely unaffected by supply voltage. Now of course if the other party is also running at a lower supply voltage, then ability to receive will obviously also suffer as the other party's TX output power will also be reduced. But for situations like listening in to Weatherman to keep track of what's going on, whether the truck is on or not isn't really going to affect receive sensitivity or range.

2. Some chase trucks may not have optimized antennas e.g. properly grounded, properly tuned for race frequency etc., which was the original topic of this thread. If this is the case, most teams are likely to achieve more significant gains by optimizing their antenna setups, than the difference seen by whether their radios are running off 12.6V or 14V. And as Bob pointed out, using sufficient gauge wiring connected directly to the battery (fused close to the battery) will help the radio make most efficient use of whatever battery voltage is available.

[Zambo]

You make good points scr but the OP wasn't about a chase truck with a 100 watt radio that shuts down for an hour or so. The guy has a 50 watt radio that he uses in main pit. I've seen a ton of guys simply using trailer batteries or even just a loose battery in a pit box to power their base radio and they're not doing themselves any favors. Again, the comparison between 14 volts and 12 volts was just to illustrate how much power is lost due to such a small voltage drop. By your own calculations that is nearly a 30% loss in power out. A guy in a stationary pit with a 50 watt radio who is having comm trouble can't afford to just piss away that much performance, especially on race day in a crowded pit where dozens of other powerful radios are operating in the same small frequency range.

[dr shaw6]

Its much better to have a good antenna than more power. Dont forget the 4-6 db gain from a good base antenna also helps.

[Weatherman]

Its much better to have a good antenna than more power. Dont forget the 4-6 db gain from a good base antenna also helps.

Couldn't agree more! A properly tuned antenna is always best. A 6 db gain antenna, (Ringo Ranger), is what I use and I seem to talk pretty far, or so people in Santa Barbara, San Diego, Yuma and a host of other places tell me! Power output is also very important when trying to talk the farthest, so then it seems to appear that the antenna and the proper battery output would be the best that could be achieved?
Now lets talk about antenna height above average ground level. The higher the antenna the farther the communication! Now lets throw in a Zinger! Your antenna was tuned for Smith's Team @ 151.xxx and now you are chasing for Joneses Team @ 159.xxx and your antenna is no longer properly tuned. A good radio not seeing a good antenna match is going to attenuate it's power to save the final transistors, (that make all the power), from too much heat so they don't smoke! What I am saying here is that a 110 watt radio with a properly tuned antenna will put out 110 watts, (the smith example). Now change frequencies to chase for the Joneses and your radio maybe putting out 60 watts! So what is the answer? Multiple antennae? Broad band antenna that would accept the different frequencies but no gain? Speaking for myself, I use three different antennas tuned optimally for the three radios I employ doing the Weatherman Relay. Antenna #1 does the low frequencies from 150.xxx ti 153.xxx. Antenna #2 does the high frequencies from153.xxx to 159.xxx and antenna #3 stays on the P C I Customer Channel, (for P C I Customers only). These antennas have been previously tuned for maximum preformance on all the frequencies being used and are re checked upon erecting them on the Weatherman Relay Site.
In summary, I would talk to P C I Scott, I think some of me rubbed off on him. I personally like the idea of two radios in every race and chase vehicle and two antennas, (properly tuned and identified of course as to which radio they belong to). If you can't employ two radios, I would certainly employ two antennas if you are using substantially diferrent frequencies.

So much information, maybe something will rub off and you can communicate over the range on your radios that P C I Customers enjoy. Providing the P C I Customer correctly utilized what P C I provided.

[Weatherman]

Never have had good radio communications from main pit. I thought it was because of using a 50 watt radio but I have seen some posts that mention properly tuning the antenna. How do you tune the antenna?

Thanks

There are several factors that can cause not so desireable communications. I will outline some of them: 1) Improper antenna, 2) improperly tuned proper antenna, 3) Inefective power supply including cigarette lighter plug, too light guage power cord, bad connector/s, and/or not enough battery supply capacity or voltage. 4) A radio not intended for the purpose you are putting it to.

Call Scott Steinberger @ P C I Race Radios - 800-859-5636.........................