Aviation Rx

[sam2]

I built this receiver **broken link removed** and it works well, but in the middle of the dial I get a strong police signal(Though I do get aircraft above and below this spot on the dial).I did not know the police broadcast on these frequencies(118-135Mhz).
Would it be hard to build a roof mounted antenna for this receiver? The artical for the receiver recomends a scanner antenna, but I would like to build one if possible.

Thank you, sam

 

[JimB]

Your link to the receiver does not work.

At a quick guess, the reason you are hearing the police in the middle of the aircraft band is due to a spurious response in your receiver.
All radio receivers will have spurious responses to some extent or another, cheap receivers have lots of big ones, the more expensive well designed ones have a few small spurious responses.

JimB

 

[HarveyH42]

Some police have aircraft... Traffic airplane, helicopter... Besides, aren't government agencies exempt from civilian restrictions?

 

[Nigel Goodwin]

The receiver is fairly simple, and doesn't have tuned RF stages, relying on a crude 'band pass' filter on the input. This means image rejection won't be good, the police frequency may be 21.4MHz away from the tuned frequency (up or down depends which side of the carrier your local oscillator is).

 

[JimB]

Some police have aircraft... Traffic airplane, helicopter... ?

A good point.

Besides, aren't government agencies exempt from civilian restrictions?

Generally, no. Only those carrying out covert operations, and they dont exist anyway!

JimB

 

[audioguru]

Look down your street. The tall police radio antenna tower or all the police cars driving by are overloading the input of the receiver since the input doesn't have AGC.

 

[sam2]

Thanks for the responses.
I thought it might be police helicopter or plane too ( we have alot flying around here in the San Francisco bay area), but from the conversations (calling in plates,and dispatchers telling units to go to certain locations, I know its all ground traffic.
The funny thing is, I only hear police stuff from a city 15 miles away and the city I live in is 250,000 people.
JimB, I tried the link again and it still works for me?
Thanks again, sam