Connect a single antenna to multiple SDR. No Switch!
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- Опубликовано: 20 сен 2024
- We explore the "multicoupler" and "drop amplifier" - two slightly different devices, that essentially do the same thing. There are multiple names for basically the same dingus, drop amplifier, distribution amplifier, multicoupler. The big difference is some are oriented more towards cable-tv usage. News flash - CATV frequencies are well within the range of an SDR, and include 2m/70cm/33cm/23cm.
These are designed to take a single RF input, and output to 2 or more receivers at the same time, with no loss of signal.
TV Amplifier - amzn.to/3D5PuR0
MFJ 8504 Multicoupler - bityl.co/GnJl
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Thanks Jim for making me look in a lot of boxes in the basement for one of those things. I didn't think about using one of these, but this might solve a couple of problems.
You bet! Morten, I've had that CATV dingus forever. I literally had never used it, been in blister pack for years. I was amazed at how well it works doing the thing.
Great tip Jim. I have a 6 port unit with build in amp for my free to air TV outlets that we no longer use, I may check it out and re-purpose it!👍🍻😉
Go for it! It's all RF, and other than the band limitations on some units (no HF), it works great.
The TV amp probably has 75ohm terminations on all the ports. Not sure how much that will effect the signal being that its receive only.
Appears to be PHILIPS/MAGNAVOX PM61116 10dB Signal Amplifier 1 In/4 Out I just got one on Ebay new for $21.47 shipped.. GREAT Video Jim ..
Thanks for sharing the model. That is gonna be it, i wondered if it was phillips. I'm pretty sure it was a radio shack or wal-mart buy from 25 years ago. Literally been sitting in a box o junk here.
I think the MFJ unit does not have enough isolation between the output ports. Typically SDR rcvrs do not have anything much between the mixer and the antenna, so I suspect they are very noisy.
Yeah, I was seriously under-impressed with the MFJ unit. That old TV amp worked very well.
Thanks Jim. I have one of those tv distribution things that I used a while ago that sitting in a box somewhere. Now that I'm using sdr's again I need to pull that out. One question, since both state that they go up to 900MHz, have you tried using it for adb-s tracking since that is 1090 MHz?
I haven't. For ADS-B you'd probably want a 1 to 1 solution. It's a specific antenna, tuned to a specific frequency, for one purpose, not really general purpose listening. It probably has a filter above the 900mhz specs.
Might be a Phillips SWV2116_17
I kept some of these for an hdtv antenna. I'll have to check if I still have any.
That might be right. I've had this thing in a box for probably 25 years.
hi i was just wondering where you purchased your diamond discone antenna i saw 1 on ali express for 70-80 dollars and wondered if youd go with that or go to a officail radio site and get it for 160-170 dollars?
Dylan, I probably got it from Amazon or GIgaparts. Most likely Giga.
Great video. thanks! Any major reason you would go unity gain as opposed to 5-7db gain? Probably doesn't need it gain I imagine, but there certainly less selection of unity gain units out there. Some Commscope units etc.
You seem to have improved the sync loss / errors etc, Are you getting over signal loading? Thanks!
I honestly didn't even consider gain. With a decent antenna, I'm well within range of the P25 system that I monitor. I was a little surprised at how much better the tv amp worked, but it also does add some gain in. As for signal over load, that is a possibility, but I really don't think so. Standing outside with my SDS-100 scanner in hand, it works ok, but not super good. I do seem to drop conversations here and there. Add in to all of this that I'm connecting to a simulcast, which can cause issues for a lot of scanners to decode well.
I'm wondering if the amp that did not work as well was over driving the SDR? Any reviews of the different under $100 dollar SDRs comparing them for performance?
I don't know how much difference it makes and probably not much for receive only but that tv/cable distribution amp is going to be 75 ohms and most antennas and sdr's are set up for 50 ohms. have you done any testing to see if the impedance mismatch is affecting the performance?
I haven't - honestly man, it works so well as it is, I didn't see the need. My criteria for that is what I had showed, using to SDR dongles and piping all that in DSD plus. P25 decode requires good signal, or you start to lose traffic. And, like you say, I don't believe it matters at all on RX only.
@@FEPLabsRadio thanks for the reply, I have a couple distribution amps and had thought of trying them out but thought I'd need some impedance matching adapters which I don't have. So I've been moving the antenna from between several sdr's depending on what I was trying to receive.
Every time you switch between 75 ohm to 50 ohm you lose about 5% of the signal. So this setup likely loses 10% of the signal. To be honest with him using a discone antenna (no gain) it's not really a high performance setup so the 10% loss is probably not noticed or made up with the additional gain from the preamp.
To be clear for his use this setup is totally acceptable. If he was trying to do some weak signal work the shortcomings would be apparent. If you are using the cheap RTL-SDR dongles out there and want to hook a couple of them up this is a fine solution. If you are running higher end SDR receivers you would be better served with a proper 50 ohm signal splitter. If you need more gain then add a preamp (LNA) that is powered via a bias-T. Most of the high end SDR's and even some of the cheap ones will power the preamp over the coax so you can place it near the antenna where it will do the most good.
On receive this matters so little that it is not worth bothering about.
Edit; especially a mismatch this small