Ham Radio - Do antenna tuners help with shortwave listening?

Ham Radio - Do antenna tuners help with shortwave listening?

 

With the tuner in it increased signal strength. Did it not also raise the noise level? I am less concerned about signal strength, but striving to signal to noise ratio. Did that improve or stay the same?

 

I'm no expert, but I would think that both noise and signal would be changed equally. I'd think that a tuner would be helpful to increase the signal over the noise level in the receiver if needed, but again, I'm not an expert.

 

If the mismatch loss is roughly 20 dB or more (a very high SWR), the RX noise is often stronger than the input from the antenna, and in that case a better match is dictated. Otherwise, for SWR's less than, for example, 10:1 or less, there is no difference. VA3RTG is correct that it is the SINR that is key.

The SINR from the antenna remains the same and a tuner does not change, in any way, the power pattern of the antenna.

 

Happy Holidays to you too Kevin. From a Fort Wayne expat in Canada, VA3CQG

 

HI JIM,

THANK YOU FOR SHARING THIS FB INFORMATIVE VIDEO.......BRAVO.......

http://www.listenersguide.org.uk/swl/antenna-tuning-units-for-shortwave-listening/

https://forums.radioreference.com/threads/antenna-tuner-for-reception-too.140190/

 

I always use an antenna turner when SWLing. While the background noise will increase with the signal level, I use the RF gain to cutback on the background noise and, depending on which radio I am listening on, use a DSP filter to improve the clarity of the audio.

 

Unfortunately this video is factually incorrect. Improving the match does not improve a receiver's ability to detect SWL transmissions--unless the SWR is very, very high (see my response above).

Modern HF receivers are relatively noiseless, but if the SWR is very high, the input from the antenna is of order or less than the noise of the receive itself. THEN an improved match gives improved detectability.

A more TYPICAL example--If the SWR is, say, 5:1 or 10:1 --again, for example-- it is the signal to noise ratio of the TRANSMISSION to tthe SKY NOISE or INTERFERENCE 'NOISE" that determines detectability of the transmission. So a conjugate match with an antenna tuner doesn't change that at all, for practical purposes.

In noise theory, this is discussed as the 'noise figures' of the antenna and the RX ,detectability is defined by bandwidth and 'integration' time.

Nice discussion in the video about how a tuner works, but this key point on receiving is unfortunately incorrect, save for huge amounts of mismatch from a very high SWR..

73
Chip W1YW

 

I found the video misleading. He implied with words the SWR match was horrible because the impedance was not 50-ohms. However, if you observed and know what the numbers mean the impedance ranged from 25 to 250 Ohms.

 

Here's a simple thought experiment you can do that proves the above.

First, just as a rough guide, here is a table of some VSWR values,, and the mismatch loss (in dB):


SWR (approx)mismatch loss (dB)
18:1 ... 7
9:1 ... 4.5
6:1 ... 3
3:1 ... 1.25

Put a variable attenuator betwe3n the antenna and the RX port.

Set the attenuation to infinity (or very high)

Listen to the receiver. That noise you here is only from the receiver, and thus whatever goes INTO the receiver has to be stronger than that for you to hear anything

Set the attenuator to zero. You will then hear fairly loud signal (if you find one) with a certain signal to noise, from sky noise and interference.

Set the attenuator to 1.25 dB. You will hear the signal with the same copyiability only the volume will be less intense

Set the attenuator to 4.5 dB. You will still hear the signal with the same copyiability only the volume will be reduced some more

Set the attenuator to (in this example) to 7 dB. At this point the noise of your receiver is just as strong the input from the antenna, so the signal is very noisy as the receiver noise and the sky noise together swamp the signal itself.

The last example shows that the mismatch loss (7dB)from a very high SWR (18:1)weakens the input signal from the antenna so it is below the noise level threshhold of the receiver. THIS is the case where a tuner would help.

In most practical cases,a tuner adds no improvement to copyiability.

73
Chip W1YW

 

Does a tuner or pre-selector act as a "notch" or "bandpass" to help reduce wideband/broadband noise or reduce overload, etc.? In the old tube days many commercially made receivers featured a "antenna trim" type control.

 

Yes. I have used a low power (cheap) antenna tuner to dramatically reduce the amount of images that are heard on 1960s portable solid state multi-band shortwave receivers, whose front end design often fails to reject intermod and other signals that are far from the frequency being monitored.

 

Everyone is answering this question as if SWR or mismatch was the only thing that using an antenna tuner in a receive mode would correct. I agree that it's one thing a tuner does but the tuner does other things!

There are many other wideband RF noises that an antenna tuner would definitely help reduce. I live .4 of a mile from an AM Radio Station. When I connect an antenna analyzer to my dipole, It pegs both meters and the analyzer is unusable. Can you imagine what any receiver that I attach to that antenna sees?

160 meter signals are difficult at best and barely above the noise. However, inserting my antenna tuner in line allows me to easily tune 160, in fact it's nearly normal. On 75 meters the band is perfectly normal but if I bypass the tuner the ADC receiver overload indicator comes on. The receiver becomes unusable.

So if you are looking for a tuner to improve the signal to noise ratio for receive purposes by correcting the SWR ... I agree that it does not.

BUT ... If you are looking for a tuner to improve SNR by lowering the level of wideband noise picked up at your antenna affecting your receiver .. absolutely it will!

 

If you want to use a tuner for rejection, you may be very surprised to see that the LC settings of the tuner, when going for the best rejection, will seldom correspond to the LC setting for a conjugate match. Will leave it to the interested student to explain why;-)

 

Simple, what I do is I put my tuner in "Bypass".

At that point, there is not point, everything is equal, it is what it is.