This is an Audio Project that i have been trying over the years that is not to difficult to do.
Using an op-amp with a high pass filter to filter out low frequency noise. Be cause i live right to a busy road and that can be a pain in the ass.
Also it needed some form of cut off when there was no signal deteted
so was working on a squealch device a few years ago and re kindled my intrest once again.
So as you have worked it out...is to listen to the birds when the sun goes down or rises..or other sounds in ones garden that the mic will pick up depending on the squealch setting.
The latest is a stereo one that uses only about 300 micro amp into an ear piece with no squealch so that it can be operated with a battery at about 9 volts and small caps value with a high quality op-amp the op group like Bur-Brown.
Also i have decided to do a transmit Audio listener with a small TX board for 88-108 MHz. Iam using this at this moment in time and the front end of ths transmitter need an preamp to it to make it more sentive to low level audio. Also ihave 3d printed a mounting board that will hold the Battery/Tx unit...
Tx Board and mount with battery holder.
This tx setup works very nice and when i have some time to make up the preamp board then get it made in China to do in the autum . Top View
I have been working on a vhf 1/2 wave Dipole for this band and have nearly finished stage one in the design of.
Waiting for some high quality coax and some cable to arrive then i can test it and make adjustments where needed. At this moment iam making the 3d mount.
The antenna will be suited for the tx boards that have a 50 ohm output and this should go a further distance
These Inverted V Dipole should have some gain over a quarter wave. More info... when constructed .
Showing the mount and other connecting Hardware.
I have put a lot of time and effort into making this Antenna getting it to a low vswr as one will see in the next Pic.
Antenna mounted on some Bamboo Canes wich is ideal for adjusting to the correct angle
This Antenna is for txing on Fm Vhf band 87-108 ish part of of the spectrum .
The elements use quite some thick copper wire and i think this should be good up to a 100 watts of power.
Iam hoping to recive a 5 watt Transmitter from china soon and do a final test before i sell them on ebay for about £18. each...What a bargain . 10/07/2021.
Reading on my nano vna Meter
With a vswr of 1.09 @ about 108 Mhz that is a good low value to be at.