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- Опубліковано 29 жов 2021
- This video answers the question - "Can an antenna switch be used in reverse, to switch multiple radios into a single antenna system and, is it safe?" The answer is - YES, in most cases - as long as the switch grounds the unused inputs, which is usually the case. The video takes a look at the numbers, describes how much isolation is needed, and then shows how to measure the isolation using a NanoVNA, and finally shows the results using a couple of HF radios. Notes from this video are here:
www.qsl.net/w2aew/youtube/coa... - Наука та технологія
Awesome as always!
Timely for me, too. I realized the other week that the local AM broadcast station is putting about +20 dBm into my rig (at the end of a long run of coax) when I use my 80m EFHW. I knew it was swamping the radio but hadn't thought much about it damaging things! Back to the AM broadcast filter build with me (for which I've been your fast pulse generator that I built the other day).
I'm lucky to be a ham in the modern era where things like the NanoVNA and TinySA are available and when great education like this is available on demand on UA-cam.
Thanks as always for your amazing explanations, W2AEW! 73 de AB4EN.
World-class exposition. Well done!
Your my favorite ham radio UA-cam channel.
Love seeing the Nano used for things other than antenna tuning. It inspires me to use mine for other things. Thanks and 73s!
Great job explaining some commonly asked question Alan, thanks for taking the time to do so!
Have only recently stumbled across your channel, and I get valuable information with each new video I view. Thanks for the effort!
Very detailed and clear as always. Thank you for the great videos.
Excellent demostration. Thanks for sharing.
Would love to see a disassembly of such a thing, assuming the switch is different from a normal DC/AC/Audio switch to keep capacitive coupling down.
Note how nobody have questions to what you actually showed us, because that is as always clear 😃
Watch temp offline he did
Another 'light bulb' learning moment for me! Alan, thank you so much for doing this demonstration. I always wondered about the bleed over. It also answers so many questions concerning these antenna switches for multiple radio hook ups to one antenna.
Very nice video, great topic, would love more on this. 👍👍
Always a pleasure. Thanks Alan!
Thanks for this. I've always wondered what I can do, now I can test my switch to be sure its safe!
Great timing. Just sold our old QTH and moved into a new temp one here in NH. For the first time ever, I built a window pass through with three UHF bulkhead connectors so I can play with a few antennas without just running coax through the window. I also wanted to swap other rigs into an antenna and have my first 2 position switch. I never thought about the isolation ratings.
I have two of the same switches. (4 ports) I like the isolation on them. Great video!
Great presentation! Thanks for the information. I'm going to go test all my coax switches :-)
Thank you for the clear explanation!
An excellent video once again, I must admit I have never checked the isolation.
Excellent thank you much
I used the same alpha Delta switches you do
Thanks! Simple, useful and interesting as always)
Excellent video! Just quickly tested my MFJ-1700c with my vna and got between 81 db (@ 1MHz) to 59 db (@ 150 MHz). The specs claim more than 60 db between 1.8 and 30 MHz. Internal construction is pretty decent for MFJ. I guess maybe I should do a video on measuring it on the MFJ-1700c and showing it's internals...
Glad i found this video!
I have an older MFJ switch, that looks perfect on the outside. I was receiving cross-talk between the two antenna positions.
Upon disassembly,I found the guts of the switch covered with a fine oily substance.
Removing he oil and abrading the electrical "ground" surfaces inside the switch repaired the problem.
I don't have a VNA, but I estimate that the isolation improved by almost 40 dB.
Execelent video, as always. Thanks!
I've disassembled the blue MFJ-1702 low cost switch because of an intermittent connection; it's not great. You are better off purchasing the higher cost antenna switch such as the MFJ-2702.
Thanks for the video Alan. 73s
KN4JWZ
Alpha Delta switches are well built and reliable. My shack has four. Thank you for showing us their performance.
A great content, Alan! I really enjoyed watching this Video. Thx for sharing your experiences with us. Happy monday from SW-Germany & 73's de Your Friend Uncle Guenter
Fantastic tutorial. Just what I needed. 73, Mark WU6R
Excellent thank you so much for doing this work .
Great explanation. Thanks.
Thanks for the upload! :)
Hi always great info here, thanks.
Thank you for sharing, I have to thought of using a nano VNA to test my switches. Yes you should look at your specs of your switches to know your bandwidth of your switch.
Great video, thankyou.
So helpful as I enter the world of a coax switches
Make sure they're shorting switches, and in proper working order before using them to switch between radios.
Would the MFJ-1704 be considered a shorting switch per your definition? I believe so but am not certain. I have a lead on (2) for $100 used. Planning to use with 4 50w UHF VHF radios. For access to all 3 most common ham digital modes for simplex contesting (Winterheat).
@@cchalfantusa Yes, according to the manual "If the switch is turned to an active connector, the other connectors are automatically grounded." It is rated to give at least 50dB isolation at 500MHz, so should be good for your VHF/UHF needs.
@@w2aew thank you so much. Would it change the equation if one of my two switching needs was using HTs? 3 5w HT’s, connected to the switch then to a VHF amplifier (40W) before the antenna? Just wondering if HTs need even a higher level of isolation because they likely aren’t built as robustly. I’ve got a FT-70DR, Icom 51A, and TYT MD-UV380. Again for coverage of all 3 common digital modes on simplex for a monthlong contest.
@@cchalfantusa I really don't know about the robustness of the HT frontends, especially the inexpensive units like TYT, etc. You'd have to see if they spec a maximum RF input. I would suspect that the 50+ dB of isolation of the switches would be sufficient, but can't be sure without knowing more about the specific HT max input ratings. Given that the switch would only be handling low power before the amp, I would expect it would be fine.
Alan, fantastic video and explanation. Your efforts are greatly appreciated! Dad used switches similarly as I remember, but they were round ones, either old B&W or some home brew ones. This was in the 70s-90's. I've been using 2 Alpha Delta 4 position switches, one to select between radios at the desk and one between antennas at the window. This setup has worked well. I am reconfiguring the window switch to select between UHF/VHF antennas, as I will shortly have only one HF feed line out to a remote switch (MFJ) at the tower. Just a thought....testing a remote switch's isolation would be a great "next episode" for you! 73 stay safe. de Cliff W3KKO
PS Great Kenwood station!!! I've had a burning desire to get an 870, they're just a great looking and sounding rig.... maybe someday!
Nice test of the switch for those working DC to daylight or Hf to 440. It's tought to find a switch that works that high to test.
Thanks for a very well researched and presented video It's something I've been concerned with for some time but not had the opportunity to research in detail . I stopped using switches and reverted to a patch system after a switch destroyed the front ends of two QRP radios. The cause appears to have been poor earthing of the unused port when the switches wear in constant use . - The switches being of the type you refer to as the MFJ but come in various brands. Would be interesting to see an internal comparison of the construction between various switches . Richard G3UGF
Good class.
At HF frequencies, it always amazes me what can be "gotten away with". At VHF, we have to start playing by the rules, and then up at UHF, everything has to be pretty spot on, otherwise it simply won't work.
I have access to some pretty frightening test gear at work - I'll have to do some similar tests with coax switches up at UHF and se how it compares to the commercial combiners we use.
Very nice video Alan, thanks a lot. 73s Pasquale IW0HEX
Nice video, thank you :)
As per normal..... 'no nonsence' & 'to the point' . Experiece really shows & makes it effertless . Thanks
thank you!
Thanks for another great video.
My experience is that things get worse when devices and/or antennas are not properly terminated (bad SWR)
Thank you. That was educating. I will go with the alpha delta. Not good to "punch holes in the envelope ." N0QFT
Thank you, Thank you, Thank you
Good Job..
just lovely
I've been wondering if my Alpha Delta can be reversed. No more switching coax for me. Thanks a ton
Hello Sir, I love your videos on NanoVNA, they are very informative, however I couldn't find a video where you test the coil antenna. How could we correctly calibrate and measure a loop antenna with wireless single loop hooked up on channel 0? It would be really helpful
Thanks Alan. Always thankful for your teaching. We never stop learning. I have wondered about just how much isolation there is on these switches. Wondering also what happens if someone has a high SWR on the common antenna port and if the isolation is still good with higher RF voltages due to the miss match. Thanks, Terry, WA0DTH
Not sure, but my gut tells me it may only be a few dB worse.
Hi Alan,
How timely. I want to be able to switch between my FT450 and a Flex 1500 into my antenna system that uses an Ameritron RCS-8V remote switch. You have shown it can be easily done with a manual coax switch. Think I will go with the Alpha Delta for the added protection. You and the family stay safe. 73 WJ3U
I've actually often wondered about this question - usually these are used to switch one radio between 2 antennas... I've wanted to have 2 radios connected to 1 antenna and I've been concerned about transmitting 100w (or more) directly into my other radio through a bad switch.
You can test the switch - either with a NanoVNA as I've shown, or even with simply a low-power RF source and your receiver.
Yet another great video presentation!
Thank you for generosity sharing.
btw - How does the LibraVNa compare to the Nano?
And… Have you ever seen/used the “Mini-1300” antenna analyzer?
Thanks!
Sorry, I don't have any experience with the LIbraVNA or Mini-1300
Just finding this video now, interesting, I've just purchased a remote control switch MFJ-4712 from DX Engineering, but my purpose is to run a Transmitter capable of 1 KW into one port and a receiver into the other port with the common port to the one antenna. I hope the isolation will be good enough can't find any spec for that so I'll have to do similar tests...good video thanks indeed. Clint - VK3CSJ
Any thoughts on Veritasium's latest video on propagation of electrical power in circuitry? It seems the internet is confused about transmission line theory.
Oh man. Yagis pointed in every direction, take my money!
Would there be any more isolation between ports that are not adjacent to each other? Example: more isolation between ports 1 & 4 vs. between 1 & 2?
Could be, it's definitely worth checking out.
Is it possible in this setup to add a dummy load to the unused radio, in case it is inadvertently activated? It would seem that it would be prudent to do so.
Wish I saw this earlier. Just had a potentially expensive mistake. Was operating off my Yaesu FT-450D and wanted to switch to my Kenwood 520-S. I have my antenna feed like connected to a meter/dummy load combo which I then connect to the transceiver. I went a little to quickly and connected the end from the dummy load meter to the Kenwood - inadvertently connecting them together and proceeded to try to tune up the Kenwood finals- didn’t realize my mistake while trying to troubleshoot the plate reading until the FT450 started smoking. So far Kenwood seems ok, but not receiving anything on 20 meters through the Yaesu. A lot of QRM right now on the Kenwood so going to see if it is still dead reception after the bands clear up. Crossing my fingers.
Ugh! Mistakes happen. Hopefully the damage in the Yaesu isn't too extensive.
Oh no! I am sorry for your loss.
My first ham radio when I got licensed in 2011 was a Kenwood TS-830S. Great radio I need to dust off and make some contacts. Love your videos! I'm new to simNEC and want to purchase an inexpensive with decent dynamic range (70 - 80 dB) up to 500MHz. Is the nanoVNA V2 plus4 worth the $299 on Tindie or are there any other reliable sources? Thx de NO5X
Everything i read says UHF connectors(PL-259, SO-239) are antiquated and not suitable for modern VHF and up radios, yet almost every VHF/UHF HAM radio sold in the states today has an SO-239 output. Is it worth changing these out for a good quality BNC/TNC/SMA/N-Type connector?
Can you do a video with some real world comparison between these coax connectors?
love the videos, thanks
Would you please clarify something? I understand that when you say the switch sends the unused port to ground that the it is sent to the chassis of the switch. Should that switch be sent to watch ground?
Yes, the unused ports short their center conductors to the shield, which is the chassis ground. This is usually grounded because it is common to the equipment ground.
Hi, where did you found the set on null action sma sma male to sma female (avoid to destroy thos on the v2plus4 vna) ?
They are often called "connector savers". Here is one example: www.minicircuits.com/WebStore/dashboard.html?model=SF-SM50%2B
@w2aew Alan, could you do a video how to property measure power output of a radio? Imagine you were getting ready to sell an Icom or Yaesu, and wanted to verify the power output on all bands, or even if you just purchased one maybe. How would an average ham (eg not everyone has a bird 43) properly verify the radio is operating and putting out proper power on all bands?
Some years ago you did a video about the RF Milivoltmeter Boonton. I bought a model Boonton 92B with the original RF probe (same S/N). But the probe cable need to be soldered again. Do you believe that if a small wire lenght (in the probe cable) were cutted off and a new soldering were done in the plug, this action could change the factory values?
I think this will be fine.
Great video as always - Thank you! “The unused port is grounded” Very curious to know how you ground your station from the second story operating location.
The only ground I am able to have is a electrical safety ground. I use a balanced-feed antenna, so no urgent need for an RF ground.
Excellent video Alan. I've been hoping you'd do a video about this subject for awhile now. By the way, there was an article done in QST on this subject awhile back (QST March 2020, Page 36), testing the newer generation MFJ RF switch (MFJ-2703). Using a separate RF Generator and Spectrum Analyzer, depending on the HF frequency (range from 3 to 30mhz) the port isolation ranged from -79db to -129db. It would be interesting to know if your NANO device could confirm those isolation readings for this newer MFJ RF Switch in this article. KF4HR
The NanoVNA doesn’t have that much dynamic range.
Just answered a question that popped up regarding my antenna management! I'm not sure I understand completely what " XdB of isolation" means, however. If you have 60dB of isolation between position one and position 2 and your reference is -73dB yet your signal is +2dB at what point in dB of the signal do you not have enough isolation? Immediately upon hitting -13dB things will start smoking? Or, is it more a rule of thumb that you're over taxing your circuitry as your xmitter signal rises though -13 and up? I still new at this. Sorry if this is a question with an obvious answer. Thanks again for a great educational video.
The rule of thumb I was using was that an RF power level up to 10mW, which is +10dBm, is safe for the receiver. For most HF receivers, an "S9" signal level corresponds to -73dBm. Since +10dBm is still safe, this says that the input to the receiver can be as high as S9+83dB and still be safe. The math shown in the video (and here www.qsl.net/w2aew/youtube/coax_switch_isolation.pdf) says that if you're using a 100W transmitter, then having at least 40dB of isolation is sufficient to keep the receiver safe.
Teardown to compare the two switches and what make one better?
The Alpha-Delta is certainly higher quality.
Allan, those sma cables look awsome. Where would I find a set. I really need to upgrade...
Here are some good ones... www.minicircuits.com/WebStore/dashboard.html?model=FL086-12SM%2B
@@w2aew thanks very much and thanks for this video. It's just what I neede to show a new ham how to test his switch to see if he can use them in reverse on his vhf radios.
Do you think there is any difference with the switch grounded to the station ground
I wonder about this also.
Could someone dumb this down for me? I want to hook up my base gmrs radio and digital police scanner to one antenna. Can I use an alpha delta switch (2 port a&b) to switch back and forth between scanner and gmrs radio to use one at a time. I currently disconnect the antenna coax from back of radios and move it back and forth and it's a pain in the A. Not sure if it matters, the transmit radio is only 20 watts.
Thank you in advance.
The likelihood is yes, you can. But, it would be prudent to check the allowable maximum input level into the scanner to be absolutely sure that the small amount of leakage in the switch will still be safe for the scanner. You would also want to verify the amount of isolation provided by the switch at 470MHz. To be extra save, you could put an extra switch inline between the scanner and the main switch - this would give you an extra measure of isolation....
@@w2aew excellent. I like the idea of an extra switch in between. Thanks
Did you calibrate each port on the VNA separately?
I ran thru the typical OSLT calibration.
Do you run a ground strap to your switches?
I generally don't. But, if you were using it as a primary antenna switch, and you switch has a gas-tube lightning protection plug, then it wouldn't be a bad idea.
Where did you find the PL-259 termination?
It's actually a PL-259 to N-female adapter, with an N-terminator on the end of it.
Which vna model are you using here???
It is a NanoVNA V2plus4.
So I have a quick question about your video...... Is it still safer to turn off the power to the other radios or does it make no odds I'd they are on or off
For most radios, nothing is disconnected when turned off, so they aren't any less immune to damage when off.
@@w2aew OK thanks I have 4 radios and I want to run them off one vertical antenna thanks I'm glad to see your video as I was unsure as to whether or not it would effect the other radios
@@29fb040 It would be wise to check the switch carefully to ensure that it has the proper isolation
@@w2aew I plan to run a president lincoln 2 plus off one of the other ports for a while.... As it can easily be replaced if it don't work we tested the ports for any continuity with a multi meter and there was none and unused ports are all grounded so see how it goes running two radios on it with the lincoln plus 2 as a scarcraficial radio just in case as I don't have your fancy meter to test it
1:10 Re: Max input +20dBm or 100mW or 1/10 of a watt. Some hams have damaged their FT-991A, blowing up R1005 which is 150-ohms and 1/10 watt. That they've damaged a resistor that is 1/10 watt, and conservation of energy, all this implies that they've exceeded the recommendation of Mr Sherwood and subjected their poor little radio to something above +20dBm.
Interesting, since less power would be dissipated in the 150 ohm resistor than a 50 ohm resistor (since the source is a relatively low impedance voltage source.)
So does that mean the whole switch is only usable "in reverse"? I'd like to get a 4 way (not including input port) so I can have two antenna ports, one for transceiver, and one for my nanoVNA - would like to bake the nanoVNA into a small go-box.
Sounds like you need a pair of 2-way switches, wired together, so you have two inputs and two antenna ports - wired like this > -
@@w2aew Awesome thanks!
How much worse does it get in the 70cm band? Is it still safe? Sorry, I’m a newbie. Just got my tech license a few weeks ago.
It does get worse as the frequency goes up. The only way to be sure is to measure the switch you have at the frequency you intend to use it with.
Well, I have a NanoVNA but I still have a lot to learn in how to properly use it lol. I have a GMRS and HAM radio both 50 watts that I’d like to connect to the same antenna. I’ll try to find some more videos on how to program the nanoVNA to run this same test.
You had me until the end. Maybe I don't understand it, but when you keyed up the top radio, if the antenna switch was isolating X amount of dB, they why would the signal meter on the bottom radio go S9 +20? Shouldn't it stay close to nothing?
S9+25dB is about -48dBm that is going into the receiver. The transmitter is doing 100W which is +50dBm - therefore there is 98dB of isolation between the transmitted signal and the signal seen by the receiver.
@@w2aew ok. thank you.
Was wondering the same thing, thanks
Got be 550 will it be safe to run two radios three this got 520s. And ts 440
Sorry it's b w 550
@@benjaminmeadows1380 I don't know, I've never tested a B&W 550 switch. If you can find a datasheet on the switch, it would tell you if the unit switches the unused inputs to ground, and what the isolation is. Otherwise, you'd have to test it.
It's my understanding that S0 is -73dBm for frequencies under 30MHz. For frequencies above 30MHz, S0 is -93dBm. So does that imply the safe input voltage for frequencies above 30MHz is 0dBm, or 1 mW? Or, for frequencies over 30MHz, it safe to go 113 dB over S9?
Actually, S9 is -73dBm for 30MHz and below. According to Rob Sherwood, 0dBm is safe on all the HF radios he has tested. Personally, I'd keep it to -10dBm maximum.
@@w2aew Thank you!
👍🙏🙏🙏👍
Very interesting what happens if you put 1 kw into it ?
Never mind lol
@@Kc8qdq All good, provided the switch is rated for that kind of power.
Pardon my ignorance but if the rigs that aren't being used switched off do you even have to worry about it?
Switching a rig off will often times *not* disconnect the antenna - so the front end may still be vulnerable.
@@w2aew Gotcha, thanks! 73, K8JLW
Is there a diseqc switch type system for UHF/VHF?
I don't know what "diseqc" means.
@@w2aew used in multi satellite setups.
@@w2aew a method of controlling a remote device (like a switch) via coax this by sending an OOK 22kHz signal up the feeder. en.wikipedia.org/wiki/DiSEqC. I am not aware of ham gear utilizing a method like this, are you? It seems to me that it might be difficult to use in a transmitting environment.
@@Piotr_P_M I am not aware of any amateur gear using this technique.
What, you want to _coax_ me into using that switch safely? *badum, tish*
Depends on the switch., I fried an SDR trying to pick up the signal uaing a cheap switch, when using an unconnected port as a SDR input.,
Yes, definitely depends on the switch - hence the reason for this video to show you how to test the switch.
Does this matter if the 2nd radio is off?
In most cases, even if the radio is off, the electronics of the receiver front end are still connected to the antenna and could be damaged by high power.
@@w2aew thanks! I tested my switches and even the worst cheapest switch has 60 dB of isolation. I never run more than 100 w so I'd say I'd be fine. Thanks so much for teaching this as I now have a very very valuable skill.
I have more than one rig and when I use a antenna switch to select which radio I am going to use, I always modify the switch so when not in line it will not go to ground. It is inline at the radio point so 100w would be the max the switch will see. In most cases being I use an amp, my radios are set to 45w out max.
Yikes! You are removing the connection to ground for the unused ports? That is a BIG part of the isolation offered by the switch, and you're subjecting the unused radio to a lot more coupled power.
@@w2aew not if it’s powered off which always the case. having it grounded is a big issue if you power up the radio you want to use and forget to switch it online.
@@slickman1953 Unless your radio has a relay that disconnects the antenna when powered off, then your electronics are still going to see the coupled power, potentially enough to do damage. For me, I never turn on a radio and transmit before listening, so it would pretty clear when I am not switched to that rig. To each his own.
@@w2aew Accidents happen, it's human nature. Oh, and by the way, grounded ports have nothing to do with isolation
@@slickman1953 Understood, accidents do happen, I agree with that. I disagree with you about the grounded ports. Grounding the unused ports will affect the isolation offered by the switch. Stray RF in the cavity of the switch will couple more energy to an open unused port than it will to a grounded unused port.
How do I rig 2 antennas with one coax
Don't. It isn't gonna be good.
This is a good analysis of the problem and I agree with your conclusions. I wonder whether your 530 S meter circuit is accurate enough to be trusted. Have you checked the S meter readings from a calibrated signal generator at the levels involved. Ie. is S9+25 db = -73 dbm + 25 = -48 dbm actually indicating s9+25 on the meter? Most manuals I have looked at suggest calibrating the s9 position but the rest of the scale is an unknown and for some radios, quite imaginary in terms of accuracy! (Liked and Subscribed) 73 Andrew VK1DA
I had checked the S meter in the 830 a year or two ago, and it's scale above S9 was close enough for this approximation.
@@w2aew OK - so few people do that! Good to know.
Didn't understand a word! But that is my fault. I will work on it and try again!
Wait a sec...is that a Nintendo DS stylus you're using?
could be... it came with the NanoVNA...
@@w2aew Interesting. The only thing I got with my NanoVNA was a guitar pick!
@@vitaflo I got the guitar pick with my NanoVNA-H4. But, the NanoVNA V2plus4 came with the stylus. I like the pick a little better, because it was easy to "tether" to the unit. I feel like I'm going to lose the stylus at some point...
Yep it's a DS stylus. I doubt any other stylus was mass produced in higher quantities by so many manufacturers
DS Lite 😑
I've used both good and not so good switches and they all have problems with them. Much better to have dedicated antennas to rigs.
Just keep in mind that an antenna that is transmitting nearby to another antenna can couple a LOT more energy into that antenna than you'd see by using a good switch. It all depends on the type, position, distance, etc. between the multiple antennas.
@@w2aew my antennas are about 80 ft apart
@@wireworks616 The type of antenna (dipole, vertical, yagi, etc.) as well as their orientation to one another, the bands of operation for each and the frequency of operation, will all have an impact on how much transmitted energy gets coupled to the other antenna. Certainly worth checking on all combinations of operating frequencies. You'll likely stay below +20dBm, but definitely worth checking out. Some of us (alas), don't have sufficient property to mount multiple antennas at decent distances between them.
@@w2aew I have one vertical on one side of the house and another on the opposite side. I did that so they wouldn't interfere with each other
@@wireworks616 That's good - still worth checking the amount of coupling though.
Microsoft Flight Simulator has been destroyed by the PC Xbox App... RIP Flight Simulator. I won't return to FS until the Xbox App is dead.
Alan Wolke, can it be convenient to leave your email address?