The AM Forum

This may have been covered before, but I could not find it.
I am wondering why not put a low power antenna tuner on your receive antenna to maximize the incoming signal? I luckily have separate transmit and receive antennas, and it occurred to me, why don't I "tune" the receive for the desired frequency.  Has anyone tried this?

Majority of boat anchor receivers have a 'pre-selector' control, which does just this.
 I know my received signal is much higher when I am working the antenna 'matched' to the frequency.
 Seems like your theory should prove true.
 73 Ed

You may maximize the signal level, but assuming there is no overloading of the receiver input taking place that would be eliminated by the tuner, no improvement in the signal-to-noise ratio (SNR) will take place. So, your S-meter might push further to the right, but you won't hear any station better than without the tuner.

There are some exceptions to this where certain receivers do not work well with an antenna impedance varying much from 50 Ohms. Most boat anchor receivers do not fall into this category.

Sometimes tuning an antenna is done to reject unwanted signals. In certain cases, notch filters might be used to block interfering signals from nearby broadcast stations, for example. High levels of RF, even on other frequencies, can put enough voltage at a receiver's input to cause safety diodes to conduct, and that can cause harmonics to be heard throughout the amateur bands.

You might also experience two strong b'cast signals mixing to create interfering signals on the amateur bands. Notching either one will usually solve the problem.

Impedance mismatch on reception is not critical as it is with transmitting.  We aren't concern with maximum transfer of power and the losses are minimal.

As already mentioned there are other advantages though to use a tuner for reception.  In my townhouse beset with RFI from neighbors, peaking the tuner often helps reject this noise.

Its a good idea, and I think its part of the problem with some modern stuff.

I use a very high Q tuned circuit in my home brew receivers with a link input.
Large B+W coil stock and a variable cap, and its amazing what it rejects without any distortion or noise.
Most boat anchor stuff was lower Q I think because of the coil size.

Modern wideband systems rely on the dynamic range of the front end and the A/D converter. The sum of all of the energy coming into the passband which could include ALL signals in the DC- 50 MHz band, for instance, will limit the ability of the radio to handle any one signal. The big advantage is the ability to "see" and process multiple signals at once. So any means to limit the bandwidth of the front end will have a positive effect if you are only interested in a small part of the spectrum. Rack tuned front ends such as that found on older high end receivers like the R390A have this selectivity built in. But in order to monitor 5 signals, you would need 5 R390A's!

If half the effort put into making huge power or special audio was invested in good receiving equipment and receive antenna optimization things would be very different. My No 19 trnscvr which is WWII set is very sensitive to antenna tuning on rx mode as are some of my other stand alone rxs. I did not appreciate the importance of rx antenna design and tuning till I installed my beverage for Rx on my non-transceiver rigs.  That was a huge eye opener and made me pay much more attention to rx antenna stuff then I used to. Now I tune every thing. I had no idea what I was missing and how much.
I often now work folks I would not have heard before I got it. Sometimes I switch to an untuned normal Rx antenna which is still up just to see. Often there is no detectable signal while the optimized system provides workable reception. RCVing antenna most over looked part of ham radio.
don

Yes, a good specialized receiving antenna can make a difference, sometimes a big difference. Many though, produce the improvement not through any tuning, but because they are directional. Most beverage designs are untuned, broadband systems.