Antenna Tuner?

[paulmohr]

Ok, in a few of my threads some of you have responded about using an antenna tuner, or variable attenuater on my home made dipole and 325p2 scanner. I am going to be perfectly honest here. I do not have a CLUE what these things are, how they work, what they do or how I would go about using one. Ok I have a basic idea of what they do, they make scanner "think" it is seeing a 50 ohm load if I don't actually have a 50 ohm antenna, right?

But I don't know what that means in terms of how it would effect performance and how I would go about using and adjusting it. I tried to do some searches and what little info I did find just confused me more. I did quick search for antenna tuners on yahoo and was seeing these complicated looking devices that are twice the size of my scanner and cost between 130 and 600 dollars! Someone mentioned a variable attenuater for 10 bucks. Is that the same thing as a tuner? And I honestly wouldn't know what one looked like if I saw it.

So realistically how would one of these effect the performance of my scanner? Minor difference, big difference or "holy crap, why don't you have one of these yet !". And if they do make a perceivable difference can someone recommend a brand/model for me to look for since I really don't what I am looking for. I am pretty sure I probably don't need a 200 dollar antenna tuner for a simple scanner and dipole antenna ( I hope). Maybe something a little more budget oriented like 25-50 bucks. And if it would make large difference I would consider one of the 100 some dollar models.

And please link me to some easy to understand information on how to use it if I were get one. Or explain it if you want to take the time. I am sure it has probably already been explained before though, I just can't seem to find it in a search. And anything I find on the internet is geared more toward ham radio and tuning them to transmit. They are saying to key up your radio and tune the device. Well that kind of isn't an option with a scanner lol.

Please help me see the light on these magical devices.

 

[SpugEddy]

An antenna tuner would have no real effect on a scanner
since a scanner is a receiver only and not a transmitter.
The purpose of using the tuner is to lower a transmitter's
SWR by creating the illusion of a 50 ohm antenna.
By creating the 50 ohms and lowering the SWR, the "reflected"
power is reduced on a transmitter.
example; transmitter output is 20 watts with a high SWR the
reflected power back to the radio will be high (possible damage
to the radio)
The same 20 watts output with a low SWR (since the antenna
tuner is in place) will have much less reflected power back
to the radio. The antenna tuner itself is now buffering the reflected
power thus saving the radio

 

[KK2DOG]

No need for a tuner, variable attenuator or anything else if it's only a receiver / scanner.
Simply hook-up an antenna and rock and roll!

 

[Ubbe]

Variable attenuator is a must for all scanner users. I wish I knew this when I started with scanners 30 years ago.
It is so easy to adjust the attenuation while listening to a weak station and dialing in the best reception.
They are so cheap to buy that there is no excuse for not using one. In europe and UK they are $5 but
the one in the picture are from amazon and is $15 so there must be others at a lower cost.

I would like to see a scanner that used an electronic attenuator with setable values for each frequency band.
And also a semiconductor antenna switch that could set each band to use one of 4 antenna jacks.
That would be super. If the front-end of scanners didn't had that black resin blocking the access to components
it should be relatively easy to add this yourself.

/Ubbe

 

[jonwienke]

I disagree. Attenuators and filters are only necessary if your radio is having trouble with interference from nearby FM/TV/pager transmitters. The BCDx36HP receivers are very good at dealing with this, and in most cases they don't need anything special in the antenna feedline other than good quality coax.

In some (but not all) cases, an attenuator may be useful when trying to receive a simulcast system, but that is not a guarantee, and putting an attenuator on the antenna will degrade reception of everything else, even if it improves reception of the simulcast system.

 

[SpugEddy]

I disagree. Attenuators and filters are only necessary if your radio is having trouble with interference from nearby FM/TV/pager transmitters. The BCDx36HP receivers are very good at dealing with this, and in most cases they don't need anything special in the antenna feedline other than good quality coax.

In some (but not all) cases, an attenuator may be useful when trying to receive a simulcast system, but that is not a guarantee, and putting an attenuator on the antenna will degrade reception of everything else, even if it improves reception of the simulcast system.

If that's the case (which I'm not arguing) how would you adjust your tuner?
My antenna tuner requires you to key the radio and then adjust for the
lowest SWR reading. With no transmit how would you adjust the 'Tune"
and "Load"?

 

[KC4RAF]

As others' have posted, you don't need an antenna tuner. That device is mainly for transmitters to match the antenna.
If you cut a wire for say 2 meter scanning, 34 inches long, it will perform nicely. Whereas if you were using the same wire for transmitting, it would be too short and then a tuner would be used.
An attenuator use only if you're near a transmitter that's overloading your receiver.

 

[SpugEddy]

Scratch my last post as jonwienke was referring to attenuators
and NOT antenna tuners. I misread his post