SWR Meter tuning question

[Duramaxman]

I a have a question about tuning my pro 106 and RS Discone antenna to try to pull in a desired freq.On the instructions it's says that it comes with extra length for tuning.the only thing is that I don't know how exactly to use my fancy new RS SWR Meter. The freq I want is 460.22500, will someone please walk me thru the steps slooowly? Thanks!

 

[nd5y]

You can't use a SWR meter with a scanner or any other type of receiver. SWR meters only work with transmitters.
Discones are extremely wide bandwidth antennas and don't need to be tuned.

 

[Duramaxman]

The instructions that came with the discone antenna says" to properly tune your antenna , you need a SWR Meter." then goes on to give the steps to do so, it even has charts and graphs showing freq curves vs swr.

 

[nd5y]

What is the Radio Shack part number of this antenna?
This doesn't make any sense. You don't need to tune a discone unless it is the kind with a vertical whip on top for low band and in that case it won't help reception on UHF.

 

[Duramaxman]

 

[nd5y]

You totally misunderstood it. You didn't read this part:

To ensure your antenna works with a minimum standing wave ratio (SWR) on all channels in the 6-meter amateur radio band, we allowed extra whip length for proper tuning.

That is only for the 50-54 MHz band. There is nothing you can do to that antenna to make it work better on 460 MHz (UHF) except move it around to different locations and see if reception improves.

If you went out and bough the SWR meter just for that you wasted your money.

 

[Duramaxman]

20-043, and thats exactly why i kept the receipt.

 

[Duramaxman]

Well answer this question for me, why can i set out in driveway in my truck with scanner hooked up to regular cb antenna and pick up the freq in question and others around it clear as bell?

 

[nd5y]

There are too many variables for me to answer that without seeing the installation in person.
You could have the discone antenna mounted in a dead spot. That's why I said to try moving it.
There could be something desensing the scanner on the discone but doesn't happen in your driveway because the CB antenna, or being in a different location, attenuates the interfering station.
You could have bad coax or bad or improperly installed connectors.
It could be several other reasons.

 

[Duramaxman]

What size coax to u recommend for a 75 ft run, for the setup i have?

 

[nanZor]

You are looking for a problem that is not there. The tuning instructions are only for 6-meters. The frequency curve charts are for reference, although I could see how one might misinterpret the need for tuning for UHF, which is not needed with that discone. That antenna is really TWO antennas - low vhf is covered by the vertical whip, and anything above 108 mhz is covered by the actual discone itself. Many who have no need for low vhf sometimes remove the whip altogether.

In the charts, you'll see that the swr curves follow a gentle pattern, and don't go above 2:1 swr anyway. You really have no problem. If the chart was extended, you'd see that 460mhz wouldn't be above 2:1.

The CB antenna is acting like a long-wire antenna. Long wires have many lobes to them, and you are either getting lucky, or the signals are so strong that even a paper-clip would work. Your discone is doing fine, and is a good choice for the job.

 

[nd5y]

I can't answer that either. How far away is the station you are trying to hear? Is it shadowed by terrain?
You could spend hundreds of dollars only to find you you can't recieve it anyway becuase it is beyond line of sight or a nearby broadcast transmitter or something is killing the scanner.

It depends on how much money you want to spend on coax and connectors and how much signal loss you are willing to tolerate.
For a 75' run on UHF I would recommend something like this: Heliax Coax - LDF4-50A but you might get acceptable results with RG-6 cable TV coax.

 

[W2NJS]

The written instructions you received with the SWR meter and reproduced in your post are inadequate and faulty. The correct way that step 2 SHOULD be written is: "While transmitting, measure the SWR on the lowest and highest channels." I echo what was said above, which is that an SWR meter is of no use in checking the receive status of an antenna. One of the instruments that can be used to check the resistance of an antenna system is called a noise bridge, which requires a relatively sophisticated receiver but will tell you if your antenna and feedline's radiation resistance is 30, 40, 50, 60 or 70 ohms (or anything above, below, or in between).

 

[w2smw]

The key word isTRANSCEIVER

 

[kb2vxa]

At Radio Shack you have questions, we have blank stares.

What's confusing you is the nature of my game. Pleased to meet you, hope you guessed my name.

Sympathy For The Devil who wrote that manual, obviously not a ham. The tuning instructions are for the 6M band and only the FM portion at the top end is channelized, if the proper word "frequency" was used you wouldn't be confused with CB channels.

"Well answer this question for me, why can i set out in driveway in my truck with scanner hooked up to regular cb antenna and pick up the freq in question and others around it clear as bell?"

MY question is what is the frequency in question? My other question is what makes you think a discone is in any way comparable to a CB antenna? Since it's a no way Jose you're making an unfair comparison.

I came up with the very same pdf on line and this antenna is a typical scanner/ham combo, a ground plane for 6M and a discone for 2M and 70cM. The VSWR curves are for reference only, the 70cM is fixed and the 6M is adjustable and varies with how long you cut the whip. The last one is as useless as (the usual bovine comment) as all it shows is that a discone exhibits multiple resonances which should tell you it receives some frequencies better than others.

Oh, give Snagit a try, taking a screenshot looks a whole lot better than photographing the monitor.

Snagit, Mac and Windows screen capture software from TechSmith

 

[Duramaxman]

The written instructions you received with the SWR meter and reproduced in your post are inadequate and faulty. The correct way that step 2 SHOULD be written is: "While transmitting, measure the SWR on the lowest and highest channels." I echo what was said above, which is that an SWR meter is of no use in checking the receive status of an antenna. One of the instruments that can be used to check the resistance of an antenna system is called a noise bridge, which requires a relatively sophisticated receiver but will tell you if your antenna and feedline's radiation resistance is 30, 40, 50, 60 or 70 ohms (or anything above, below, or in between).

Thats all i needed to know, all the rest was just as confusing as the instructions. Im new to this and yes im gonna ask dumba@s questions. I figured my moneys as good as anybody elses. Thats why i pay for membership...

 

[kb0nly]

Thats all i needed to know, all the rest was just as confusing as the instructions. Im new to this and yes im gonna ask dumba@s questions. I figured my moneys as good as anybody elses. Thats why i pay for membership...

Don't get discouraged! Those Rat Shack manuals suck. Most of the time all they are trying to do is sell more junk! LOL..

Although that antenna is actually a pretty good antenna! I had one up for my scanner for years and years, until they started going to 800Mhz here and i needed more gain.

Keep asking dumb questions, if you don't ask them you never learn and the questions stay dumb!

As for your questions on the coax, you said a 75ft run right? I would get some good RG6 double or quad shield and use that, yes you will need an adapter to go from the F connector that you commonly put on RG6 to go to the UHF connector on the antenna but they are available. And yes the RG6 is 75 ohm coax when you should be using 50 ohm coax. But remember, your only receiving, a slight mismatch of this nature will only affect the SWR on transmit, your not transmitting. Its a big difference between receiving only and transmitting too.

The RG6 is a really good choice for scanner antennas. I know lots of guys using it. As for your question about receiving it better on the CB whip... If your still talking UHF it could be that the CB whip being such a poor antenna at UHF is helping to attenuate some interference, where as the discone is so much better of a wideband receive antenna that the scanner is being overwhelmed by some strong nearby signal which is causing problems with the frequency you DO want to monitor.

All you can do is play around with the antenna mounting location. Get it outside, in the clear, away from metal objects and power lines, etc. Then see how it does. And keep asking questions!

Have Fun!

 

[n3vbj]

Pro 106+SWR

The SWR tuning your referring to is for using the Discone antenna for 2 meter or 440 Mhz transmitting if you are a licensed amateur. you can not tune the antenna for receiving the antenna will do fine for your application without tuning. If your trying to receive Baltimore Co digital an outdoor antenna is not recomended.

 

[majoco]

A "tuned" antenna - your CB whip - will always outperform an "untuned" (AKA broadband) antenna - your discone. Better to get an antenna that is the correct dimensions for the frequency you wish to receive.