PROOF The MFJ-1708SDR SUCKS (T Connectors Vs Power Splitters)

[@g1lbu948]

One thing you neglected to mention Jarrard is that on transmit the MFJ will short out the SDR output socket to eliminate any RF getting to your computer. It does what it is supposed to do! Apply RF to the mini circuits and there wont be much of it left. They are both designed for entirely different functions.

[@1967deek]

Spot on👍

[@davep6977]

I was on a 144 SSB net last night when I decided to rearrange some equipment (MFJ-1708B) and ended up by-passing the 1708B and connecting my antenna directly into my receiver. My rx improved. So I did a test with a beacon station on 144.287 which is 162 miles away straight across Lake Michigan. With the 1708B in line the signal is S3 to S4 (SDR port open) With the antenna directly connected the beacon signal is S7. Same antenna. FYI- the reason the SDRF port is open is because I have my SDR Play connected to a G5RV I'm not using via a length of 75 ohm RG-6 and it works great on all bands with a signal strength comparable to my ham rigs (HF & VHF) As was note around the 19:00 minute mark. I don't need to be on a dxpedition to deal with weak signals. I'm 40 miles east of Chicago (where is the net is) and most the stations have there beams pointed everywhere but east toward me. Ever try talking in to the back side of stacked 13's ? Great video. Found it looking up spec's on the 1708B. 73 W9DLP

[@ppi57]

Can you revisit this with the newer MFJ-1708-BSDR device?

[@MrZerohour1967]

I'd be interested to see someone test the B version. The manual claims "Excellent isolation between Transceiver and SDR Receive ports". So I'm assuming they got their asked kicked by the customer base for failing to put a Wilkinson style splitter in the 1st version.

[@NinjaInTheFirstDegree]

Is there a modern 400-520 mhz model, particularly for GMRS 460- 470mhz? Can't even find these 1708s new from what I'm seeing

[@user-su5sq5ib3i]

So MFJ came out with a 1708B, is this the model you tested or is this the older version? I believe they have added more switching relays and changed up their layout a little bit.

[@oldjarhead386]

I have measured 5 db loss to the receivers. When used with a diplexer on a rig like an TS-2000 the losses can be as much as 9 db. That’s at full scale signal to an audible s0. I don’t like 5db loss, 8-9 is totally worthless to me at least.

[@DaveNT9E]

I bought an MFJ-1708SDR and SDRPlay at hamvention and it smoked my SDRPlay. I purchased a refurb from SDRPlay then I found out I could use a Splitter and 2 cables to the RX IN/OUT jacks on my 7600 without having to mod the IC-7600 . I use the Mini Circuits ZMSC-2-2R which has a range of 0.0020-60mhz which compliments my Icom 7600.

[@RateMyRadio]

Dear Dave, sorry to hear about your SDRPlay. We believe you're not alone and MFJ have redesigned the unit completely to properly seperate signals with 'their version' of an Mini Circuits splitter. Personally, we much rather use the same setup as you with our IC-7610 if needed. 73, Jarrad VK3BL :)

[@RateMyRadio]

Here is a great graph showing the signal loss of mismatched receivers connected to a parallel 'T Connector' style device like the MFJ-1708SDR: drive.google.com/file/d/1r61IoHewQKbJlszmbOdFpXVIoXqitovw/view, and here is some further reading about why a power splitter is required: www.dxing.info/equipment/rolling_your_own_bryant.dx MFJ would seem to make a 'proper' version of this product, which addresses my concerns, the MFJ-1708B-SDR. Thanks to a viewer Manuel for pointing this out. www.mfjenterprises.com/Product.php?productid=MFJ-1708B-SDR is the one to get, and whilst we haven't tested it, the schematics indicate it should be suitable for all but the weakest of signal work, where no splitter should be used. :)

[@anthonyrosa5006]

Dumb question, Does the output change once you connect the PTT. I thought the PTT switch switches the output from the radio to the SDR and back. I could be misunderstanding the function of the device. Also, if you use the power splitter will the output of the transmitter then damage the SDR device that is listening or does it temporarily silence the SDR receiver as is the intent of the MFJ device? I'm just trying to figure out what the proper way to set up an SDR receiver alongside a Transceiver with minimal complications and best performance. Do you have a good recommendation? Considering an RSP Duo or Dx. Thank you.

[@sstorholm]

What would be the “proper” way to connect an SDR to the same antenna as your transceiver? A small buffer stage before the SDR with a very high input impedance and 50 ohm output impedance, along with a relay arrangement to disconnect it on TX?

[@PhilippeRoselle]

I've been using the MFJ-1708B-SDR with a Yaesu FT-991A and a SDR NOOELEC. I see a signal attenuation of 3 to 4 S unit with regard to a direct link between the transceiver and the antenna (by-passing the 1708B-SDR).

[@jy5iqmas219]

I had the intention to order one of these (MFJ 1708 RF Sensing TR Switches) and now I am a little bit confused, I think it suppose to isolate the 2 receivers when you push the PTT and Triger the relay inside, please elaborate on this.

[@RateMyRadio]

The MFJ1708SDR WILL NOT Isolate the receivers, the MFJ1708B-SDR WILL. Just make sure you get the 'B' version (released in may) and you will be happy. 73, Jarrad VK3BL :)

[@ve5uo]

Great demo, Jarrad. Good application of simple test equipment to compare the passive device with the commercial and MFJ product. Thanks!

[@RateMyRadio]

Thanks for the kind words! I stumbled a bit with my words at times but thankfully the test gear was there to get the point across :) 73 Jarrad VK3BL :)

[@djryder2002]

MFJ= MIGHTY FINE JUNK! Great video, I purchased the Mini Circuits ZCS-2-2+ Thank you.

[@thormusique]

Thanks for the video! So here's a question: Say that we use a quality power splitter instead. What's the best way to go the step further and provide the necessary relay by which to ground the receive signal when transmitting? Thanks!

[@RateMyRadio]

Its actually quite a complicated topic; I wish there was a way to combine a splitter with the MFJ product but there isn't it really needs to be done internally. Essentially what you want is the antenna to go into the splitter during receive, then during transmit you want to remove the antenna from the splitter and connect it to the transceiver directly. So you need 2 relays, a splitter, and a design that provides adequate isolation for the splitter and second RX while transmitting. Its not that hard to do, at least it shouldn't have been for MFJ, but they went down the 'works well enough to sell' path rather than the 'works best practice' path like they should have. 73, Jarrad VK3BL :)

[@thormusique]

Yes, that makes sense. Thanks for the reply!

[@RateMyRadio]

Dear Thormusique, I have good news :). MFJ HAS made a product that combines the splitter/isolator with the relays, its called the MFJ-1708B-SDR, and it costs a mere $20 more. I haven't tested it, but the schematics look promising. You can find it here: www.mfjenterprises.com/Product.php?productid=MFJ-1708B-SDR. I dare say it was a later revision produced because of critiques such as mine :)

[@vidasvv]

Does the MFJ-1708SDR claim that it offers any isolation ? DONT THINK SO! A quick look at the schematic shows that both inputs are connected in parallel and theirs no "power splitter". I did a quick check on my RSPduo and found the input impedance ranging from 35 to 80 ohms on 20 meters so I decided to check out a few more rigs that I have. Flex 5K is abt 52 ohms, Flex 6600 is 36- 70 and the FT 817 was 66 to 67 ohms.

[@RateMyRadio]

I'd say the fact they released a 'B' version with proper isolation almost straight away due to customer complaints speaks volumes in my opinion. Both inputs in parallel is by definition a voltage divider btw. 73, Jarrad VK3BL

[@W8ASA]

Thanks for the video. Of course, the Mini-Circuits is 3 dB PLUS insertion loss, which isn't much at 7 MHz.

[@RateMyRadio]

Its a fraction of a dB according to the data sheet. That's the nice thing about Mini-Circuits, they publish all the data, including that of the little ZSC-2-2+ :) 73, Jarrad VK3BL

[@donr2670]

Hi Jarad! Does the 1708 "B" have your blessing? I got one today. I also had and used the original 1708 which does not share the antenna but I listen to the audio on the SDR so that is fine. What is not fine is that I cant use the AUX RCA to key my SB221 because it is grounded (shorted) in receive, and open in transmit. Can you suggest any way to change this without adding a relay in the 1708 box, which is what I think I need to do. wd8rif.com/radio_manuals/pdf/MFJ-1708_Manual.pdf

[@RateMyRadio]

It certainly does; whilst I haven't tested it the circuit diagram indicates that MFJ have integrated a proper power splitter, significantly improving the product. It seems the original version was rushed to the market and they didn't realise how many of the original buyers would end up complaining. Oh well, its fixed now and the B version is a great value simple solution. 73, Jarrad VK3BL :)

[@charlesholzer8178]

As is said earlier in these comments, you're testing the MFJ box for a function it's not intended to do. It's function is to isolate the SDR from the antenna line while the radio is transmitting, and that's all. If it was set up as a 3-db splitter, then it would dissipate 3 db of your transmitter power everytime you transmit. That would not be a desirable thing! Test it for what it's designed function is.

[@RateMyRadio]

I’d argue - and do - that splitting the signal properly is a core aspect of its functionality. It would seem MFJ agree, as they have released a revised version that does.

[@charlesholzer8178]

I will grant adding some isolation between the port for the SDR and the antenna port will help reduce any loading effect of the SDR on the signal to the transceiver's receiver input. But you definitely do not want tp put a 3-db isolation filter between the antenna port and the transceiver port. It would be there full-time bi-directionally, including when you transmit. So 3 db of your transmitter power (last time I looked, that's half) will be used making heat inside the TR switch, not a good thing in many ways. Note MFJ did not add isolation in that link. Most modern receivers have more than enough sensitivity to make up for 3 db less signal, since that's less than 1 S-unit. So if you want to put that isolation in the link to the SDR, go ahead.

[@RateMyRadio]

The problem is it isn’t always a 3dB hit. Depending on what receiver you connect to the sdr port it may not always present a 50 ohm impedance. MFJ had revised the design to provide the functionality I’ve advocated for. 73, Jarrad VK3BL :)

[@gregorystark1217]

Ok. All you have proven is that both devices would be able to listen (receive signal) for both radio and SDR. Now, does it do its job when you activate the PTT? As in does it stop the transmit signal from radio from going directly in to SDR, as designed? Isn't the device suppose to stop strong signals from entering the SDR, once again putting the input a signal in through the antenna, but, did it cross the strong signal threshold?

[@vincentmartin2528]

Thanks for the work and demonstration. MFJ is crap, and you get what you pay for. Proven yet again.

[@MrMaximuskodrata]

Hello sir, how about COMET CAS900 ? thanks

[@2wrdr]

? That is a splitter only. If you don't isolate the transmit power from the SDR receiver you will destroy the SDR.

[@1967deek]

The MFJ-1708SDR is not supposed to be a power splitter, it's a switch that disconnects the SDR and sorts its antenna input to ground and works fine but Chinese tx rx switch you can buy online now are much better i have been using the Chinese one for over a year with no problems at all.

[@sammaloney2499]

Couldnt one just use a Dow key switch , as a means to mute the rx on watetfall, with the dongle and do away with the MFJ component completely ?????

[@stevenaustin2860]

thats a blagg one thats why the mfj 1708b sdr is the one i have and there the proper ones have alook on steves k3gmm or it might be k1gmm not sure but he,s made a video about them and he says the one without sdr on it doesn,t ground out m7byf in england just looked its k1gmm 73

[@kb8apa]

A close look at the MFJ-1708SDR T/R switch (#148) by David Casler and redo your test

[@RateMyRadio]

David Cabler makes slick videos, but he didn't 'lift the lid' on this one. In fact, even MFJ know its 'limitations' or in my opinion significant flaws, and have produced a proper version, the MFJ-1708B-SDR-S. 73, Jarrad VK3BL :)

[@daveycrockett9447]

The biggest flaw this thing has i that when you transmit, your audio comes screaming through thr SDR which is very annoying. That doesnt make sense if the SDR antenna connection center pin is supposed to be disconnected via the relay and shorted to ground- at least this is the way this unit is described to be working. I cant be the only one who has ran into this annoying behavior with this mighty fine junk device.

[@cowboy6591]

The mini ciruits can only handle 1 watt 😞

[@VK5KU]

Great review. Wasn’t expecting that. However, I’m not a fan of splitting signals. Every dB counts and 3dB may be the difference to understand a call sign or not. Nevertheless an interesting product review and an even more interesting outcome. Everything you’ve explained made sense. 73 de Kevin, VK4KK

[@g0ilocalling]

MFJ stands for More F@#&ing Junk in my opinion. The do turn out some crap!

[@RateMyRadio]

I've ran one of their G5RV's for 2 years now... after the 'SO-239' burn't up when I tried to run it on 15M and I replaced it with a proper connector, its been a fine antenna. What annoys me most about MFJ is with just the tiniest bit more effort, and for a few dollars more, they could produce really useful gear. Instead they make things just good enough to sell. They really have it down to an art, and thats why I have no problem calling a spade a spade. Jarrad VK3BL

[@RateMyRadio]

The fact this particular product degrades a Ham's receivers performance yet promises to help them 'see new ones' with a band scope / SDR dongle just really pisses me off, to be frank. Hence, I went out of my way to thoroughly and truthfully comment on it. 73, Jarrad VK3BL :)

[@generozea3195]

Interesting, but could have been said and demoed in 1/4th the time.

[@RateMyRadio]

Probably Gene, but we like to cater for everyone from those who its their first time seeing a scope, to those like yourself already familiar with the concepts. 73, Jarrad VK3BL

[@bossdog20]

hi Jarrad who else is with you is there more than one of you ,why do you say or write we all the time

[@RateMyRadio]

Two reasons; 1) Traditionally Ham Radio Operators used 'we' on air when talking to other operators, probably a carry over from those who worked as radiomen and were representing companies etc. 2) We have a second, mostly behind the scenes collaborator Ben VK3HBN, who makes a 'vocal appearance' in the PR-781 vs PR-40 video. Thanks for asking, 73 Jarrad VK3BL :)

[@bossdog20]

I've been a licensed amateur operator for thirty years and have never said we or ever talked to any one else who has. must be a VK3 thing.

[@RateMyRadio]

I don't say it on air; I think it is more an American thing; check out the style of the wonderful 'DX Stories' that used to be published in the 'West Coast DX Bulletin' here: www.ve1dx.net/Stories/stories.html

[@RateMyRadio]

That is very true Jeff; thinking back on Engineering 'Prac' classes I can remember the instructor always using the word 'we' when going through the methodology. 73, Jarrad VK3BL

[@RateMyRadio]

Dear Jeff, I have emailed you as requested, and removed the previous comments for your privacy :)

[@donaldswafford6987]

IYO ... FU ... IMHO

[@KR8T]

This has nothing to do with its intended function.

[@RateMyRadio]

Yes it does.

[@KR8T]

You're comparing a power splitter rated at 1 watt to a relay meant to switch out one port during transmit. From the MFJ manual; "The MFJ-1708SDR T/R switch uses a relay, which switches from transmit to receive mode. " A better review would have been to measure the isolation on the SDR port. As mentioned at the end, you can accomplish the same thing with a relay. Exactly!

[@RateMyRadio]

I think you've missed the entire point of the device, which is to split an antenna between two receivers, unless the main receiver - a transceiver - is transmitting. What good is splitting the signal between two receivers, if it does a lousy job of it? MFJ received enough complaints about this very issue, that they released a B version, the MFJ1708B-SDR, which incorporates a power splitter to do the job properly.

[@justrailroads]

Totally agree man. I hung in there until the power splitter demo which he said was "guaranteed to give 3dB to each device" which means nothing. I think he meant "each device is guaranteed to receive a signal which is -3dB relative to the source", but hey, fair enough. The key there was guaranteed, which he admitted it didn't do. So it must have been a guaranteed piece of garbage. Then he didn't know which resistor was 50 ohms.... The output impedance of his signal generator isn't 50 ohms. The resistors he tried to use weren't precision resistors at 50 ohms. He presented a whole bunch of nothing attempting to pass it off as technical data. Which really that part I'm cool with, but the title of the video says PROOF this product sucks. He didn't even use it... never hooked a radio to it. I say hook up a couple of radios and shows us how it receives on each, then show us how it actually does disconnect the SDR port during transmit. There isn't even a need for passing anything off as technical data in that case. At that point we can hear the difference between the receivers and see that it disconnects SDR during transmit. Fact is, the device doesn't suck and works (as I think you were curious about) exactly as intended. In all honesty, he can carry on about the "B" model which still doesn't do what he claims it does, it does two extra things, using RF sense so you don't have to hook up a PTT if you don't want to, and it also shorts the receive to ground during transmit, which this unit doesn't do, nor is it necessary. It still isn't a "power" splitter. So, no, you didn't miss the point.

[@WW5RM]

Build your own! Its not hard!

[@DutchinCle]

please elaborate. Thank you in advance.

[@robt3518]

I stopped watching this after the 5th or 6th "I don't know but..." do some research before making the video, spewing "I don't know but" means you don't know and either need to do some research or not make the video.

[@mikemcdonald5147]

MFJ Mighty Fine Junk or Mississippis Faulty Junk