SWR plots on 3 Popular Rubber Duckies

[ronhl]

Hi everyone,
I have read many posts on the net on how well some of these antennas perform on various bands. I took some SWR plots on three, the RS-800 bnc, the stock bnc for the Pro-96 and the stock sma for the BCD396T.
Remember that SWR is a ratio and a 1.0:1 is a perfect match but in the real world anything less than 1.5:1 is excellent. As you can see the 1st plot is the RS-800 and has a very good match up around 860mhz of 1.4:1. The 2nd plot is Pro-96 and the 3rd is 396t, both don't have a good match at any freq band because they were mainly designed to be broadband types.I took these on a Agilent Network Analyzer calibrated from 50 to 1000 mhz.Let me know what you think because I also own the Seeker 800mhz and the Diamond RH77 but have not swept them yet.Plots are located in the files section on the Yahoo BCD396t group because this forum won't allow anything bigger than 19kb to be uploaded.

Enjoy

Ron

 

[JnglMassiv]

Can you perhaps post some screen shot images?

 

[northzone]

An SWR plot of an antenna really doesn't say much about how well the antenna works. If you were to sweep a 50ohm load (resistor) it would show a perfect swr of 1:1 across the complete range of scanner frequencies and would not receive a thing!

 

[flyingwolf]

I always thought that SWR meant nothing when Scanning?

SWR (Standing Wave Ratio) was only a concern when transmitting.

 

[ronhl]

50 ohm load

An SWR plot of an antenna really doesn't say much about how well the antenna works. If you were to sweep a 50ohm load (resistor) it would show a perfect swr of 1:1 across the complete range of scanner frequencies and would not receive a thing!

No kidding, a perfect 50 ohm load would show that and would not recieve a thing because it would be a shielded type aka "termination" otherwise its garbage so throw it out.
Obviously you don't know how Network Analyzers work and are calibrated! If you did then you would realize that open,shorts and loads are specifically used in the calibration process. SWR/VSWR or Return Loss is one of many very important paremeters(s11 s22 s21 s12) that antennas and many devices are spec'd to and have to be measured and or tuned to. I should know, its my job every day, dc to 50 ghz.Used many types over the past 20years.
A length wire will have its own "resonance" or many resonances and is such the case of many different antenna types.So don't tell people that swr does not mean much.

 

[flyingwolf]

Ok I understand why SWR is important for Transmitting. But can you explain why it is inportant for listening?

 

[Al42]

Ok I understand why SWR is important for Transmitting. But can you explain why it is inportant for listening?

If the source (antenna) and load (scanner) aren't matched, signal will be reflected from the load back to the source.

From the formulas you can't tell whether the system is transmitter/antenna or antenna/scanner - it's the same numbers, and the same loss of signal, either way.

 

[flyingwolf]

Ok Thank ya much.

 

[Al42]

Ok Thank ya much.

BTW, just in case you don't know the author of your signature, it's Stephen F. Roberts.

 

[N_Jay]

SWR is importnat, but it is NOT "all important".

Given 2 antennas of similar design and efficiency, you want the best match.

Given two antennas of different design or efficiency, comparing the SWR is nearly worthless.

 

[Roarinbear]

What's the best antenna (rubber duckie or another style) for my 396T. (137-960.000)

 

[palo1]

SWR is relevant only to transmitting antennas, what is important is that the antenna is tuned to the specific frequency that it is meant to receive. Having said that, there is an old adage that a good transmitting antenna will generally make a good receiving antenna

p

 

[pro92b]

At http://www.procom-dk.com/techinfo/e0204-swr-mismatch-loss there is information regarding SWR mismatch loss. Click on the graph for a larger version.

 

[palo1]

The loss they are referring to is the relation of input energy to radiated energy - receiving antennas do not radiate. How is SWR measured? Its the ratio of transmitted power to reflected power on a transmission line and antenna combination.

p

 

[N_Jay]

The loss they are referring to is the relation of input energy to radiated energy - receiving antennas do not radiate. How is SWR measured? Its the ratio of transmitted power to reflected power on a transmission line and antenna combination.

p

The generated signal id from the receive antenna, and that energy is delivered to the receiver.

SWR is a poor term to use with receive systems, but they still have return loss, and it is still important (just not as important as TX system).

 

[Al42]

SWR is relevant only to transmitting antennas, what is important is that the antenna is tuned to the specific frequency that it is meant to receive.

Which will make for a nice low SWR. (Unless the antenna impedance is very far from the cable and scanner impedance - like the end of a half-wave dipole.)

 

[Al42]

The loss they are referring to is the relation of input energy to radiated energy

Nope - it's the loss of signal from the signal fed in to the signal that can be used. It doesn't matter in the least whether we're talking about an antenna using the signal supplied by a transmitter or a scanner using the signal supplied by an antenna. The formulas aren't directional.

How is SWR measured? Its the ratio of transmitted power to reflected power on a transmission line and antenna combination.

No, it's the ratio of peak to trough on the standing wave - hence "standing wave" ratio. It's usually easier to measure it by measuring "forward" and "reflected" power (nothing really reflects), but it can be measured directly anywhere you can erect a parallel line at least 1/2 wavelength long.

Try reading some transmission line theory before you try to reinvent physics.