More Radio Questions

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More Radio Questions

Postby SHMIV » Mon, 12 Jan 2015 02:36:24

Before I get into questions, I'm happy to say that I have aquired the ARRL Technician Class study manual. My goal is to get the Technician License this year, followed by General next year, and Extra the year after that. Studying in a truck is proving to be a challenge...

Question: Fiberglass trucks prove to be horrible for ground plane. In doing some research, I discovered counterpoise. I read a couple of articles, in which the authors had purchased two identical fiberglass whips, used one as the antenna, and mounted the otherone upside down, underneath the first, as counterpoise or groundplane. In both articles, this application was used on a base station. That exact application is problematic on a truck that I do not own. However, if I understand antenna construction correctly, my 1/4 wave fiberglass whip is essentially a 4ft fiberglass rod with 25% of 11 meters of wire coiled around it, coils not touching. 11 meters is 433.07 inches, so a 1/4 wave is approximately 108.27 inches. Would I be able to create good counterpoise by getting 4 non-conductive rods, 6inches long, and wrapping approximately 27inches of wire around each rod (27 inches being about 25% ofa 1/4 wave)? Obviously, the wire would have to come in contact with the shielding on the coax, but not the center conducter.

2nd question: When I transmit on my radio, my voice is heard on every single speaker on my truck, even the computer speakers that I have connected to my tv, as well as another speaker that is connected to nothing. I have researched this, replaced everything but the radio (coax, antenna, antenna mount); I have an idea what the cause is, but I figured that I would ask here, first, to see what the knowledgeable ones here had to say. This is a mild annoyance to me; but to GF... well, the woman grows horns when I try to use the radio. Flaming daggers of eternal torment shoot from her eyes. Plus, I want a cleanly operating radio. How do I fix this?

Lastly, I can't really justify the fancy Diamond SWR meter to GF, at the moment. I think that I have to buy her a sewing machine, first. Maybe a diamond of her own, too. So, I got an Astatic meter. It has a field strength meter on it (theoretically) but the instructions suck. If I hadto rely on them to use the SWR function, or the power meter, I'd be lost. The field strength function isn't even mentioned. Any ideas?

I will greatly appreciate any guidance on any of these questions. Especially the one that causes my beloved to become Demon Lady!

If it helps, my radio is a Stryker SR655, the coax and the antenna mount are both K-40, and I just had to put my Firestik (Screw-tune tip; not the trim to tune) fiberglass whip back on; ice damaged my K-40.

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Re: More Radio Questions

Postby MarcSpaz » Mon, 12 Jan 2015 05:08:10

To answer question one... you need 4 conducting rods that are the same length as your whip (primary element), which if I read you correctly, is a quarter wave. These elements need to be bolted or soldered to your ground plate at the base of the primary element. Each ground element should be evenly spaced and bent downward at about a 45 degree angle for the best results.

I have never tried the method that you specifically asked about... but the wire length and each coil length and spacing would have to match your truncated whip identically to have a shot at working. Keep in mind, the closer to balanced everything is, the better your SWR will be and the better your performance will be.

Question two... a little tricky since I am not there, but we can cover the basics. You want your radio to be as close to the battery as possible, so the power lines are as short as possible. Often, RF energy can collapse into wiring for other devices, causing lots of interference. Three methods that I have used are 1.) take both your positive and negative leads and twist them together all the way from the radio to the battery.

It should resemble this...

Image

While pluming the cables, make sure they stay as close to the vehicle chassis as possible. Don't let them span free air anywhere if at all possible.

2.) Twist the wires and install them the way I mentioned in 1, but tap the ground wire close to the radio chassis with a lead less than 12" and bolt it to the vehicle chassis. You will need to scrape the paint and primer away so the clamping of the ground cable is direct metal to wire.

3.) Not my top choice, but as above, Make the ground wire from the radio chassis with a lead less than 12" and bolt it to the vehicle chassis. Follow the rules for option one with running the power straight to the battery and no free space runs.

You want to use options one, two or three for every piece of electronic equipment in the truck, as well as the 2-way.

Other problems that cause your symptoms, which is likely what you are experiencing, your SWR is likely way out of whack. Your antenna is likely mistuned to a frequency has an octet that is close to what come audio amps are sensitive to.

One other thing could be... you are just running too much power for the proximity of the other devices. I used to have a 1500 watt amp and the antenna was too close to the house. Every time I keyed up, my voice came through every piece of electronics in the house, even if they were off. My wife said the fridge would even make funny noises.

Question 3... without knowing the model number of the Astatic meter. its gonna be hard to help with that one.


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Re: More Radio Questions

Postby SHMIV » Mon, 12 Jan 2015 12:31:59

Well, the way that you've described a counterpoise sort of defeats my purpose; I was trying to figure a way to fit an antenna system on a mirror bracket.

I'll try that wire twist idea. I can't wire straight to the battery on this truck. There are factory terminals on the dash, and, if I want a radio, I must use those terminals. I am not permitted to modify this truck in any way, including running new power wire. I do have a noise filter wired in, between the radio and those terminals, though. It's made by Diesel, but there is no model number on it.

My SWR reads out ok; I've checked it on 2 different meters, and they match.

The model of that Astatic meter is PDC2, btw. Sorry about that; I thought that I had included that bit of info.

My current radio puts out roughly 100 watts, asdid my last setup. My last setup, though, gave me no problems in regards to transmitting my voice where it ought not be heard.

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Re: More Radio Questions

Postby SpanishInquisition » Mon, 12 Jan 2015 13:43:13

Unless you delve into the realm of mobile HF, don't sweat the counterpoise too much. 2m and 440 are the most common mobile bands and don't have much trouble even with mag mounts. Mirror mount should be just fine.

I am amazed that 4 watts AM or 12 watts PEP would cause so much issue with external speakers. You might try some ferrites around both ends of the speaker line to help stray RF from getting in there. Usually when this happens, the RF hits the speaker wire and the final transistor in the audio amp acts like a detector diode in a crystal radio.

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Re: More Radio Questions

Postby jdonovan » Mon, 12 Jan 2015 16:13:13

he was asking about a 70 watt 10m rig... This is HF, and its high enough power that with out a reasonable antenna system, there is going to be RF all over the DC power lines in the truck causing all kinds of interference.

SHMIV: - you HAVE to have a counterpoise to have an efficient antenna system. If you cant/don't want to you'll have to turn down the power on the radio until the bleed over is low enough to be acceptable.

The lower the frequency, the bigger the antenna systems get. Physics is a bitch, but it is the law... :clap:


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Re: More Radio Questions

Postby SHMIV » Tue, 13 Jan 2015 17:44:47

As usual, you guys are awesome. When I have time to play with it some more, I'll let you know how it turns out. Thank you :)

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Re: More Radio Questions

Postby bryanrheem » Wed, 14 Jan 2015 20:33:02

If I could do it over again, I would have studied for the General as I studied for the Technician. Just something to consider.


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Re: More Radio Questions

Postby SHMIV » Wed, 14 Jan 2015 20:52:45

Under normal circumstances, I would study all three.

As it is, trying to study anything on the truck is difficult. Studying, in general, is difficult; I'm a hands-on learner.

The new general manual comes out next year, then the new extra, in 2017. That's why the 3 year plan.

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Re: More Radio Questions

Postby bryanrheem » Wed, 28 Jan 2015 12:21:41

SHMIV, that's actually my current plan right now. General next year and then extra in a bit.


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Re: More Radio Questions

Postby SHMIV » Wed, 28 Jan 2015 12:34:05

Seems like a sound plan, to me. It corresponds to the release of the new books. May as well study the most recent material.

My cousin is excited that I am getting into ham radio. He just retired, and I think that he likes when his family members share his interests. He never married or had kids, so any excuse to spend time with extended family is meaningful.

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