Dual Rubber Duckies?

[jerneedog]

Hello all,

I was wondering if this would improve reception on a hand held scanner.

Would using this BNC Dual Connector with two different Duckies, really improve reception?

This is for use when I'm not able to hook up to my Base Antenna or Mobile Antenna.
I was thinking of using the stock Rubber Ducky with the 800mhz one from Radio Shack.

Here are pics of the connector and an example with two Rubber Duckies.

Thanks,
Jerry

 

[Concrete1]

It will "change" your reception, but it could be either good or bad, depending on the frequency & location.
I would guess that the reception would become a little more "directional", & some freqs will have gain, while others could actually be nulled out, from the dual setup.
It's probably worth experimenting with as hobby project/time killer

 

[thumbtrap]

The spacing between the two is so small for the wavelengths being scanned that I doubt it would do much to directionality.

 

[dynamitedjs]

I'd like to try it out...where did you get that dual bnc adapter widget?

 

[jerneedog]

I'd like to try it out...where did you get that dual bnc adapter widget?

I found it here.

I was hoping to find something similar at Radio Shack, but I didn't see
anything like it on their site.

I guess you could also get a T type connector (BNC T FMF) and
2 right angle (BNC 90degree MF) and fit it altogether, to get the same effect.

 

[Pro-95]

I was hoping to find something similar at Radio Shack, but I didn't see anything like it on their site.

RS 278-0112 $5.29 BNC-T Adaptor
RS 278-0116 $5.29 x 2 Right Angle BNC Adaptor

A bit more than 10 bucks but you get two adjustable right angle adaptors that you can use for an adjustable (turn-down) antenna mount if your dual system doesn't work as expected. Plus maybe with adjustable RA's you can get more seperation or directionality. ????

 

[K5MAR]

The only benefit to this that I see would be from using two band-specific antennas. Say, a 800 MHx antenna and a VHF antenna. I can't see that using two of the same antennas will do any good at that narrow a spacing.

Mark S.

 

[JohnWayne]

It will do something alright. Most likely it will be for the worse. When you do something like that then you are changing the impedance of the circuit that is your antenna/feedline/whatever. Your scanner's rx input is 50 Ohm, works most efficiently when it matches to a 50 Ohm load (your antenna/feedline). Let's take two cases:

1) Dual adapter with two handheld rubber duck style antennas: This will probably put your impedance (z) somewhere around 90-100 Ohms. This will work ok for rx, but it is hardly as efficient as a matched system where all of the received signal is coupled to the scanner.

2) Dual adapter with a rubber duck and an external antenna via a random length of 50 Ohm feedline: The best way I explain this setup is to use an analogy of ghosting on your cable TV picture. Ghosting occurs because there is a compromise in the cable line somewhere and your TV is receiving the same signal at two slightly moments in time. The audio is not as affected by ghosting, but it can still have an effect. The signal through the rubber duck will reach your scanner much quicker than the signal coming from the external antenna and through your feedline. This is because of the cable's velocity factor (VF), which is anywhere from 65%-95% that of free space. So, say your coax has a VF of 75%; that means the same signal going to the rubber duck will reach the scanner 25% faster than the signal coming from the external antenna. Just like on your TV, your scanner signal will have some ghosting now. There are some other factors, but that is basically it. You may not notice these effects on a FM analog signal, but I bet that digital control channels and such would be affected, which could result in a poorer scanning experience.

Now, with that said, there is another rub to case #2. You can do some magic with calculated lengths of coax to make stubs that will show a z of 0 Ohms. This is similar to the way that multiband HF antennas are constructed, and, to a lesser extent, multiband VHF/UHF antennas. The basic idea is to have a length of the coax or antenna that "disappears" at certain frequencies. Let me know if you want more info on that stuff, it's a lot to type and I don't want to get off topic here.

Jeff

 

[Pro-95]

The basic idea is to have a length of the coax or antenna that "disappears" at certain frequencies. Let me know if you want more info on that stuff, it's a lot to type and I don't want to get off topic here.

I'm interested! But I could read about antennas all day long. Maybe start a new thread????

 

[jerneedog]

I'm interested as well...please share.

 

[LarrySC]

Simple answer: I use a double duck on my wifes BC-780. Its not in a location for an outside antenna and what she listens to wouldnt need it anyway. THE SECRET is make sure both antennas are THE SAME. I use two PRO-95 ducks and it works GOOD. Anything else will have reduced signal level on certain bands.

 

[loumaag]

It will do something alright. Most likely it will be for the worse. ...

1) Dual adapter with two handheld rubber duck style antennas: This will probably put your impedance (z) somewhere around 90-100 Ohms. This will work ok for rx, but it is hardly as efficient as a matched system where all of the received signal is coupled to the scanner.

As Col. Potter on MASH used to say..."Horse Feathers". You have a single feed to dual antennas; hopefully resonant on different bands. This is called a multi-band antenna with a single feed. Do the antennas interact, of course they do, does it affect the impedence, you bet. Does it matter a wit for receiving--NO. The only time you have to worry about feedline load matching is for transmitting and in any case you really don't have feed line involved here as the connector is too short to be considered a feedline. Are you losing anything, well of course you are introducing some loss through the connector becuase, well it is a connector after all.

If you had two bands of interest, this probably is a good idea. Using a multi-band, wide designed antenna (such as what comes with the scanner) and another more narrow band antenna probably will not help. But if you stick a VHF and a 800MHz type antenna directly on this thing, you will certainly improve both of those bands at the expense of the rest of the spectrum.

 

[JohnWayne]

If you have an impedance mismatch, then you don't have an efficient match. If you have 0.50uV of signal that has gotten to the antenna, then that will be attenuated if you don't have a good match. You may end up with 0.48uV when you get to the scanner. Something has to be given up in the mismatch, and that is your signal. A mismatch will never damage your scanner like it would a transmitter, but it never helps your receive signal.

I think we are both trying to say the same thing though. It's not going to make any noticeable difference for receive. I know I can't tell the difference between a 0.50uV signal and a 0.48uV signal without the use of test equipment.

Having two antennas like you describe brings up another problem: resonance. A VHF antenna is resonant on VHF, and a UHF antenna is resonant on UHF. When you add/combine the two then you have a different animal. I don't know what the resonant frequency of such a beast would be, but it would surely be an interesting experiment.

This is similar to feeding multiple scanners off of one antenna. Many people simply use splitters; even cable TV splitters. But the question I pose is this: If these inexpensive splitters work so well, then why do people spend the money for proper receiver multicouplers?

One thing to keep in mind is that even though the voltage present in the antenna/feedline system on the transmitting side is much greater than the voltage present in the receiving side, there is still some voltage on the receiving end, and it wants to see a good match between antenna and receiver.

I’m not trying to argue with you, I am just disagreeing even though I still think that we are somewhat saying the same thing.

Jeff

 

[N_Jay]

Efficiency wise matching and tuning are just as importnat for RX as they are for TX. (If your antenna system is losing 1/2 the power in TX, then it is losing 1/2 the power in RX)

The only difference is that with TX, the transmitter may reduce output when it sees a bad load. I receiver will be uneffected. (Its sensitivity will not change)

 

[N_Jay]

Why do all these things "Seem" to work?

Because the people testing them don't know what to look for.

It is not much diffreent than teh performance accessory market for cars.

I bet we can find lots of people happy with their "Tornado" and their "Slick50"!

 

[nmfire10]

Why do all these things "Seem" to work?

Because the people testing them don't know what to look for.

It is not much diffreent than teh performance accessory market for cars.

I bet we can find lots of people happy with their "Tornado" and their "Slick50"!

Ding ding ding. Give this man the prize. THANK YOU!!!!

 

[loumaag]

Having two antennas like you describe brings up another problem: resonance. A VHF antenna is resonant on VHF, and a UHF antenna is resonant on UHF. When you add/combine the two then you have a different animal.

No you don't. You have an antenna system which is resonant in two areas. There is some interaction between the two and in a perfect world maybe some adjustment would be made to one or both, but in practice two antennas, resonant on different frequencies, can be fed on on feeder without adjustment.

This is similar to feeding multiple scanners off of one antenna. Many people simply use splitters; even cable TV splitters. But the question I pose is this: If these inexpensive splitters work so well, then why do people spend the money for proper receiver multicouplers?

Not in the least is it the same. Splitting at the scanner end divides the signal between (or amoung) the different outlets with a subsequent dB loss. Combining antennas at the antenna feed point is a different matter altogether. BTW, this common feed to multiple antennas is a very common practice in the amateur world where transmitters are frequency and band agile and hence is much more used in the ham community. It has almost no use in the commercial world of locked frequency spectrums.

I’m not trying to argue with you, I am just disagreeing even though I still think that we are somewhat saying the same thing.

I am also not trying to argue, just presenting the side that says not everything has to be perfect. A non-resonant antenna will still pick up a signal, a mis-matched feed system (providing you are not using additional capacitors or inductors as in a tuner which will detune the system) will work just fine for a receiver.

Efficiency wise matching and tuning are just as importnat for RX as they are for TX. (If your antenna system is losing 1/2 the power in TX, then it is losing 1/2 the power in RX)

The only difference is that with TX, the transmitter may reduce output when it sees a bad load. I receiver will be uneffected. (Its sensitivity will not change)
--------------------------------------------------------------------------------
Why do all these things "Seem" to work?

Because the people testing them don't know what to look for.

It is not much diffreent than teh performance accessory market for cars.

I bet we can find lots of people happy with their "Tornado" and their "Slick50"!

You and I have disagreed on so many things in the past I often wonder if I should comment; however, in this instance I will. If in fact your antenna system eats half a transmitter's power on transmit due to VSWR it is not loosing a similar amount on receive. That has got to be one of the most outragious statments you have ever made. You are forgetting antenna effeciency in your factoring. And besides, we were discussing a connector, not a feed system. Oh, and why do all these things seem to work. Well as Dr. Sigmund Freud said, "Sometimes a cigar is just a cigar." :lol:

 

[AZScanner]

Hello all,

I was wondering if this would improve reception on a hand held scanner.

Here are pics of the connector and an example with two Rubber Duckies.

I doubt it will improve reception (you never know until you try it though, I suppose) but using it in public will no doubt earn you some HamSexy points. :lol:

Also, you can double your hamsexy points by wearing this at the same time:

-AZ

 

[DaveNF2G]

1) Dual adapter with two handheld rubber duck style antennas: This will probably put your impedance (z) somewhere around 90-100 Ohms. This will work ok for rx, but it is hardly as efficient as a matched system where all of the received signal is coupled to the scanner.

The value would be less than 50 ohms, not more. Impedances in parallel behave like resistances in parallel for purposes of calculating combined effects.

Details, details. There would still be a mismatch. :wink:

73 de Dave, NF2G

 

[JohnWayne]

Duh, you're right. I don't know why I put 90-100 Ohms for the z. I must have been thinking about what impedance coax you'd need to feed it with for it to get close to a match. I should figure it out some time actually. It's an interesting calculation because the voltage is so tiny since it is rx only, and the frequency comes from the ether and not a transmitter directly coupled to the antenna system.

To loumaag, just because things are common in the amateur world doesn't mean they work correctly. I do agree with you that you can use just about anything as a rx antenna. Whether it works very well or not is a whole different case.

Anyways, if yall want to continue this debate, then we can. But we're never going to agree even though we are all saying basically the same thing: it will work, but who knows how well it will work.


Jeff