Split the Signal from an Antenna? - Page 1
Forum section: electronics / rf-microwave

author: Lord of nothing
author_rank: Super Contributor
timestamp: February 17, 2018, 11:09:50 am
content: HiI have an good working VHF Antenna who I could receive several different thing I want decode 24/7 include TV and Digital Radio.I could not found any Splitter that look like the could do the job.I know there are some for TV thing but I dont trust them. So can someone recommend an Product who get sell in Europe or directly from China?I have different Filter I will use.THX

author: Gribo
author_rank: Frequent Contributor
timestamp: February 21, 2018, 03:04:23 pm
content: Why don't you trust these splitters? A 75 Ohm power splitter is few $ (EU) with good enough performance at VHF. A fancier 75 Ohm splitter might even go to 2GHz with ~6db insertion loss.

author: Lord of nothing
author_rank: Super Contributor
timestamp: February 21, 2018, 05:11:13 pm
content: The have no SMA Plug on and the loss must be insane.

author: GrahamC
author_rank: Contributor
timestamp: February 21, 2018, 06:00:52 pm
content: If you were to actually be able to measure the impedance of your receiver(s) and the inexpensive TV/Satellite 75 ohm splitters, you would likely find that their impedance is only ever 50 ohms some of the time. Even the impedance of your antenna will change depending upon what frequency it is being used for.The whole of your antenna, feed line, connectors, receivers and splitters is a complex system and near impossible to maintain one impedance from end to the other on all frequencies all of the time.The inexpensive TV/Satellite splitters will work quite well for what you want to do (but don't transmit through them).You can get F connector to SMA adapters quite inexpensively, this is just one example:https://www.ebay.com/itm/192338526628incidentally, 50 ohms systems have a slight advantage in the transmission of power, 75 ohm a slight advantage in voltage. Use google and search for something like "why 50 ohms" or "50 ohm vs 75". And, there are many more other impedance's for cable besides 50 and 75.cheers, Graham

author: hagster
author_rank: Frequent Contributor
timestamp: February 21, 2018, 06:53:50 pm
content: If you stick an LNA in front you can easily build a resistive splitter that will work well for VHF and the extra loss wont matter much.

author: vk6zgo
author_rank: Super Contributor
timestamp: February 22, 2018, 01:06:41 am
content: Quote from: Lord of nothing on February 21, 2018, 05:11:13 pmMost such devices use "F" connectors which have quite reasonable specs.If you mean loss in the device, well, of course, that is the price you pay for wide bandwidth devices.It won't be that high, though, as otherwise they would be useless for their intended purposes.Not everybody lives in "line of sight" of their main metropolitan TV sites as I do, so they must be useableat considerably lower signal levels to be any good elsewhere.( I have two 2 way splitters feeding three TV outlets----one direct from the first splitter, & the other two from the second splitter which itself is fed from the second output of the first one.)

author: AF6LJ
author_rank: Unknown
timestamp: February 22, 2018, 05:19:51 pm
content: The TV splitters should work fine, just add enough amplification ahead of the splitter to make up for the loss of the splitter.

author: Lord of nothing
author_rank: Super Contributor
timestamp: February 23, 2018, 08:47:47 am
content: that:https://www.conrad.at/de/sat-verteiler-schwaiger-vtf8848-8-fach-5-2400-mhz-759672.htmlThe loss is huge...

author: chrisl
author_rank: Regular Contributor
timestamp: February 23, 2018, 09:20:40 am
content: It is normal to see ~12dB of loss when you split the signal in 8 ways.If you want low loss, get a 2 way splitter... The loss should be around 4dB.

author: TheUnnamedNewbie
author_rank: Super Contributor
timestamp: February 23, 2018, 09:36:39 am
content: Quote from: Lord of nothing on February 23, 2018, 08:47:47 amThat is actually quite good. Think of it this way: if I put 1 W of power into the device, the sum of the powers from the outputs can be at most 1 W, otherwise the device would defy the laws of physics (as it would be a over-unity device).In other words, if I split it in 2, I would be able to get at most 0.5 W from each output - or -3dB. Split that in 2 again, to give 4 outputs, and I'm at -6 dB. 2 again to give 8 outputs, and we are at -9 dB. And that is the ideal case, with no losses inside the device - in other words, an ideal splitter could never give you better than - 9 dB in this case.However, most wideband splitters use resistive techniques to provide matching of the outputs, resulting in another few db lost. So that is a perfectly normal amount of loss for a 8 way splitter.If you want better you need more complicated tricks like Wilkinson dividers - but these are far less broadband, and if you want them somewhat broadband you need multiple-stage dividers which become complex (and thus expensive) real fast.

author: AF6LJ
author_rank: Unknown
timestamp: February 23, 2018, 12:57:49 pm
content: Quote from: Lord of nothing on February 23, 2018, 08:47:47 amWell yes it is, which is why I said drive it with a pre amp to compensate for the loss. Even commercial multi-couplers use preamplification to drive these splitters.Just use a good quality LNA and you are in business.

author: james_s
author_rank: Super Contributor
timestamp: March 09, 2018, 02:41:41 am
content: Put the amp as close to the antenna as possible too, that way you're not amplifying noise picked up along the way. You'll always have a loss whenever you split a signal, even if nothing is connected to some of the ports on the splitter. This is why you should never use a larger splitter than you need.

author: AF6LJ
author_rank: Unknown
timestamp: March 09, 2018, 01:23:23 pm
content: Quote from: james_s on March 09, 2018, 02:41:41 amagreed and terminate any unused ports.

author: Lord of nothing
author_rank: Super Contributor
timestamp: March 09, 2018, 01:53:07 pm
content: The major problem is the raspberry pi generate a lot of noise.