How to design an antenna input circuit. - Page 1
Forum section: electronics / beginners

author: dhead
author_rank: Newbie
timestamp: December 16, 2012, 06:55:57 pm
content: I've got a mini usb dvb-t dongle and I'm getting very poor reception in compare to a set box,I'm guessing in the interest of lower price and more compact design some compromises made, and I could probably build a small circuit to improve the reception quality.I'm not sure where to start,First of all I would need some tools to diagnose this better,I can look (software) at the number of continuity errors on the ts stream per sec but this gives me only the end result, a corrupt mpeg ts stream.The frequencies are in hundred of MHz, so I can't use a cheap oscilloscope (which I don't own) and not something like DSO Quad.I would probably try getting rtl-sdr up and runningbut still I'm not sure how to proper diagnose this.Maybe there's a more simple solution ?But I still want to learn from the process, using an existing circuit isn't quite what I'm looking for.Any suggestions on some resources with useful information on the building this kind of circuits ? and how to diagnose this ?Thanks.

author: dhead
author_rank: Newbie
timestamp: December 21, 2012, 08:50:50 pm
content: I've got no replies so I've edit the topic.I would really appreciate any ideas and guidance.I want to design an antenna input circuit that I would be able to connect between any type of antenna and the dvb usb dongle.I've really no idea where to start, I've real basic knowledge in electrical circuits.Any recommendation on reading material ?

author: PA0PBZ
author_rank: Super Contributor
timestamp: December 21, 2012, 09:08:26 pm
content: The dongle will have an internal antenna, so it would be a good start to have a look inside. It could be on the same PCB with the rest of the circuit or it could be a separate thing.While you have it open look at what chip it uses, then try to find a datasheet and see if that tells you anything. It might have some reference design information.Without knowing what's inside it is hard to be more specific.

author: JonnyBoats
author_rank: Regular Contributor
timestamp: December 21, 2012, 10:10:02 pm
content: I have one of these dongles and it works OK (great value for the money!).What kind of antenna are you using? The simple antenna that comes with it is not nearly as good as roof mounted TV antenna. The first thing I would try is a better antenna.Next you can try an external amplifier between the antenna and the dongle, these are readily available and cheap.

author: dhead
author_rank: Newbie
timestamp: December 21, 2012, 11:50:19 pm
content: The chip is an ITE Tech IT9135, I don't think there's a reference design freely available.Although the result is important, getting a better signal.But the road to it is way more important, learning.I'm currently using the cheap and simple external antenna that came with the dongle, located outside of my window.I'm a student living on dorms so a roof mounted antenna is out of the question.From users experience there are still reception issues with a roof mounted antenna, this is the reason why I started thinking about designing such circuit.After I would have a working input circuit I plan to design my own antenna, probably pcb printed.Comparing the usb dongle to a tv tuner box, the dvb dongle got allot more signal issues, my guessing is that the compact size of the dongle adds some restrictions to the design.I don't believe that an amplifier is a good idea, the dongle has no power issues, the cable to the antenna is quite short so the antenna signal is already amplified enough, I think that adding an amplifier would only make things worse.I thought adding an band pass filter and amplify the output but this is already done by the chip when tuning to the frequency so I'm not sure if this is a good idea.I think I will try to get few tuner boxes and active antennas and analyze their antenna input circuits.Anyway I would like to get some recommendations on reading material on the subject, keep in mind this is a digital tv transmission (QAM mod').