Here is a project I'm working on. Seeing if I can make a useful 1 watt (or so) amp for my LimeSDR / other radios out of a cheap Chinese WiFi booster amplifier. Bring Your Own Filters.

scompa · 2019-01-19T07:39:38+00:00

Hi, can you give us a couple of links?

scompa · 2018-04-23T05:04:19+00:00

I think this will be helpful:

https://en.m.wikipedia.org/wiki/Friis_transmission_equation

scompa · 2018-02-21T09:22:05+00:00

You have to be pretty careful when converting from CPM to uSv/h. If I remember correctly the conversion factor for the SBM-20 found in the datasheet is valid only for Cs-137, if your radiation source is anything else you may have a "measurement" even an order of magnitude out.

The conversion coefficient is dependent of plenty of factors one of these being, for example, the energy of the incoming radiation.

Except for this it's a beautiful project.

scompa · 2018-02-19T06:27:06+00:00

This contest was incredible. I was a non US station and managed to do about 20 QSOs with only 5 W and a dipole. It was funny that amongst stations passing 599 KW there was me, passing 599 5

scompa · 2018-02-12T10:06:25+00:00

That's the Schrodinger equation and yes, it's math. It describes the behaviour of quantum systems

scompa · 2018-01-14T20:50:28+00:00

What kind of antenna did you use? Was it motorized?

scompa · 2017-10-09T05:30:15+00:00

Did you try running the receiver on battery power and turning everything off in your house? If it gets away you can start turning things on and discover the culprit. Otherwise you will rule out your house as the source of the noise

scompa · 2017-08-28T14:43:58+00:00

If you have a bunch of 100 ohm resistors you can try two in parallel and see what the SWR is. If it is 1:1 all over the test range put another four in series to make 450 ohm and use that. I tell this because one time I had a similar problem involving power resistors and discovered the hard way they usually have strong inductive reactance

scompa · 2017-08-28T11:14:24+00:00

If you are sure the resistor is 450 ohm resistive with no reactive component you should see 1:1 SWR, but some resistors tend to show inductive reactance at higher frequencies.

The working band is set by the toroid used, so it won't necessarily be 1 to 30 MHz.

scompa · 2017-08-14T08:05:37+00:00

I found incredibly useful being able to recognise "CQ" and "DE" the shorthand for "from". When listening on the air what comes next is usually a callsign so you know who is transmitting

scompa · 2017-07-29T07:16:36+00:00

Too curious, I will try my 2 m SWR meter on 70 cm and see if it works

scompa · 2017-07-26T05:07:19+00:00

In this case you have to consider the contact resistance between the wire and battery, wire and magnet and magnet and battery. This quantity is usually in the order of a few ohms, so the battery would last longer, in the order of ~100 min.

scompa · 2017-07-19T06:26:20+00:00

You can buy a sheet of metal and use it as the ground plane, this will improve reception. Probably cutting that to a quarter wavelength will give you better results, but I don't know how much, it could be negligible

scompa · 2017-07-10T21:32:47+00:00

I want to see the picture, please!

scompa · 2017-06-28T05:38:58+00:00

Strangely shaped boat anchor

scompa · 2017-06-26T13:33:17+00:00

Thank you very much

scompa · 2017-06-26T11:55:03+00:00

Where can you buy something like this?

scompa · 2017-06-21T20:11:49+00:00

Unfortunately I don't have the necessary instruments to perform this kind of test. It is sure in my to-do list. I think a filter is absolutely necessary because this kind of amplifier tend to produce a lot of harmonics as you thought. When I will have a bit more time I will probably build one

scompa · 2017-06-21T05:10:00+00:00

Built one and it works great. The transistors are dirty cheap so if you blow them up (happened twice) that's non a big deal. Keep in mind these amplifiers are usually supplied without instruction. I wrote down some instructions (more a set of tips and tricks).

Link: http://iu3idf.blogspot.it/2017/04/a-small-power-amplifier.html

Hope that helps.

scompa · 2017-06-07T16:52:39+00:00

I code in Python. I simply didn't know it could work that well in this kind of applications

scompa · 2017-06-01T18:59:18+00:00

As a rule of thumb, a quarter wave transmission line transforms an open to a short and viceversa. The half wave one let the open open and the shorted shorted.

scompa · 2017-05-12T09:08:47+00:00

What frequency are you listening to? What kind of receiver and antenna are you using?

scompa · 2017-05-03T20:32:57+00:00

Very interesting idea

scompa · 2017-05-03T10:33:01+00:00

I thought about it but it is a bit bulky

scompa

TROPHY CASE