Why QRP?

Why QRP?

The gold question "why QRP" can be found everywhere on the net. Though one may think it is obvious, I often meet HAMs with no idea at all about the bitter-sweet relation between "S" value and output power. 
"I'm getting sick and tired of struggling with with my QRP Ft-817... it is nothing else but royal pain to make even a local QSO even from a hilltop with it..." I heard. What to say for this? Let's count!

I am not going to explain how decibel works. In nutshell the most important thing is dB is not linear. What does it mean in real life? Double power does not mean double signal strength. 

The whole station in a bag

For example:

If 100W produces "S9", 25W will give "S8", 6W will give "S7" on the other side.

Okay, but what if there is strong man made noise on the receiver side?

There are several ways to get rid of man made QRM.




Narrow band antenna

High Q antenna is one of the best way to get rid of broadband noise. High level signals from other bands such as broadcast stations can be eliminated due to narrow bandwidth of the antenna. One of the best well known high Q aerial is magnetic loop. It can be used as receive only antenna as well, being switched on only when receiving. Controlling is easy using a small relay-antenna switch triggered by the transceiver.




Pre-selector

High Q tunable filters are easy to build. The best solution is to transform the signal down to a very low impedance with for example a 9:1 transformer, and after an LC filter it can be transformed back to 50 Ohm. Bandwidth is reasonable narrow, while the circuit can be used as trap to notch out broadcast signals.




Phasing noise canceller

NoiseKiller by HA5IW Simi (military painted later)

Timewave ANC-4, or Noisekiller by HA5IW Simi etc... Basically there are few mixers in the box with phase shifting circuit and a small amplifier. A noise antenna is needed to catch the unwanted signal. The phase shifting turns the signal up side down (180 deg) against the same signal coming from the main antenna, while the amplifier sets the same amplitude, therefore the disturbing stuff will simply disappear, or will be reduced to a very weak birdie.
It is very effective, and does not take to long to learn to use.
I realized that the system works better connecting a bandpass filter to the noise input as well. This way strong signals from other bands will not come into the system from the noise antenna.




Filtering local devices

Ferrite filter on the incoming
cable of the broadband router
It really does it's job...

In most cases noise comes from the grid, or from local sources, such as plasma TV, computer, led driver and so on... Finding them is not so difficult, adding some filters or in worst cases changing them to noiseless ones can help. Try to avoid low quality power adaptors and use proper grounding in your shack to get rid of the anoying noise.



Raising you voice against disturbing signal sources

Every countries have it's own authorities dealing with spectrum licensing. (OFCOM in UK, or ACMA in Australia) First of all locate the noise source. Knock on the door and ask. Offer help to eliminate the source. If the owner is not helpful, explain the situation. In case of emergency the noise is not only against a hobby, it is making the job ARES services very hard. Radio is a nice thing to waste ones free time, but also it is way of saving life and goods. 
Final solution is to call the authorities to find the noise and do their job to switch it off. 


A station can be copied only if the listening station really wants to hear!
Being able to hear is a great thing. DO WANT TO BE ABLE TO HEAR!
Get rid of local QRM and give a chance for QRP!