#195

This video introduces the RF Diplexer, which is a pair of filters used to separate RF signals on a single feedline into two different feedlines based on their band of operation. These are commonly used with dual-band radios and satellite communications, where the uplink is often in the VHF frequency band and the downlink is in the UHF frequency band.
The circuit board is shown, and the physical construction of the filter and hand-wound inductors is discussed. Then, the diplexer is connected to the spectrum analyzer with tracking generator and the capacitors are adjusted to tune the filter to the desired response.
This design was presented in the Nov/Dec 2009 issue of the AMSAT Journal in an article authored by Ron Cade W6ZQ. Ron used a program called ELSIE to design the filter.
AMSAT website:
www.amsat.org
ELSIE Lumped Element Filter Design software:
www.tonnesoftware.com/elsie.html
Video Notes page:
www.qsl.net/w2aew/youtube/Basi...

[@girishchandra2236]

Thanks a lot Sir your classes are excellent. I am working as RADAR engineer ,this video was highly useful and informative for me

[@DucatiMTS1200]

Thanks for taking the time to produce this video Alan. This insight will be most useful to me as I'm planning on getting into satellite communication next year. 73 de GI8WFA ... Wm.

[@Afrotechmods]

Thanks for explaining why you insert the attenuator after the tracking generator's output! Great video as usual.

[@smerfu8734]

It’s kind in this “wizardness” of RF magic design, nice, real explanations

[@outerealm2439]

I simply love a video that puts a smile on my face. Being an RF Metrologist for 25 yrs it's always nice to watch the "fun" on someone's workbench other than at work. I'm building a diplexer for a little EME work on the next field day and was looking for a design and this is nice and simple too. Excellent video Alan! 73 N3SWR - yes I chose SWR for a reason ;)

[@voltlog]

I like it how you do very good and clear explaining in your videos. Although I don't work much on RF, I enjoy watching your videos.

[@mickeyaslam5272]

Yet another great video. Great work and thanks Alan

[@joem5386]

Very good explanation and demonstration. Thanks!

[@MichaelLloyd]

I enjoyed this video very much. Thank you.

[@BalticLab]

Good job Alan! Enjoyed watching it. I just had to design a Diplexer for a VSAT aperture that required the 10 MHz reference clock and L-Band baseband (as well as power) to be brought into the Ku-Band upconverter using just one port.

[@w2aew]

Sounds like that would make an excellent video topic, Sebastian.

[@fdutrey]

Another great tutorial. Thanks

[@NGinuity]

One of the things I did when I bought a milling machine was also invest in a drill index. Not only do I now have capability for 30 different diameters of holes, they also double as 30 different inductor winding diameters! :-)

[@marco56702]

Thank you for this really interesting video!

[@RestoreOldRadios]

Very informative and thanks for sharing. Don

[@hamoshamradiosdr2823]

thank you for sharing us your knowledge

[@w2aew]

+Robertoh93 that is a Tek FCA3003 frequency counter/timer

[@kentvandervelden]

Nice informative video

[@fuzzy1dk]

spreading or compressing the windings on the coils will also change the tuning

[@RyanBlace]

Yeah, it would have been cool to see them adjusted too. Great video! Thanks.

[@ChipGuy]

Nicely done, thanks ;)

[@ralph9987]

as always a great video tutorial, how can i adjust the filters without a spectrum analyzer and just an oscilloscope and signal generator please. many thanks for your commitment.

[@dennisqwertyuiop]

Thanks for sharing video

[@ElecTechie]

Nice one Alan ...

[@w2aew]

Thanks Randy!

[@baghdadiabdellatif1581]

Thank you alan. Can i ask you to make a video about RF phasor Basics- Tutorial, construction

[@PY4SR]

Nice tutorial Alan. Thank you. What's that equipment above the SA? Rob PU4HAS

[@K1ZEK]

Very good video ,thanks for taking the time to make it. 73 Leo...K1ZEK

[@sanjubluerock3]

Wonderful video tutorial Alan..! Can you please share the PCB layout wish to build one this month..

[@w2aew]

I'm sorry, I don't have the PCB layout. This was a kit that I built for a friend.

[@pcfxr4u]

Thanks again! What do you use to remove the varnish from the wire ends? PCFXR4U

[@w2aew]

It depends on the type of enamel coating. For some, I will scrape it with a razor blade. Others, I will boil it away in a blob of molten solder.

[@Anemalwozere]

THANKS FOR THE INFO what caps are you using and board where can you get them more info please

[@urlkrueger]

Great to see the actual effect of adjusting filter components. But now I'm really confused. I can see a VHF signal entering the board and then splitting between the two filters. The VHF filter passes the signal on to the antenna but what happens with the UHF filter? Is the VHFsignal absorbed, in which case you lose 1/2 of your RF power or is it reflected back which could wreak havoc with your VSWR? Good ol' mind numbing RF.

[@w2aew]

The UHF path presents a high impedance at VHF (generally), so does not load the VHF signal. The path length is very short, so there are no problems with reflections or SWR.

[@AccessControlForum]

thanks!

[@victornpb]

neat but I wonder if there's anything you can do or clever trick to get things like this at least close enough if you didn't had a spectrum analyzer and func gen.

[@w2aew]

It's a little tricky if you don't have a signal generator. You can make up for the SA by possibly using the FFT function of a digital scope... If you don't have any of that, but just some VHF/UHF radios - then you could just do some spot checks and adjustments of signals through the filters with the radios...

[@hobbified]

I've always been curious - how is the response of one side of the diplexer affected if the other side is left open-circuit (after the network) instead of properly terminated?

[@w2aew]

Most often the return loss and transmission loss will be affected (higher SWR, etc.).

[@SeAfasia]

Thanks Alan, Next time can you prepare a tutorial for swr meter?

[@w2aew]

SeAfasia It's on my list, but not sure when I'll get to it...

[@SeAfasia]

***** I'll waiting for it Alan..

[@ajithpeter3040]

Hi Alan, Just wanted to know if one can use a diplexer in reverse i.e. two radios in two different bands connected to the two ports and a multi-band antenna connected to the combined port ? and also performing simultaneous transmission and reception ? If that is possible, what all aspects should one look into while designing such a filter ? Thank you !

[@w2aew]

Simultaneous transmission and reception on two separate frequencies is the most common application for diplexers and duplexers (the latter is typically used in the same band - where tx and rx frequencies are much closer together).

[@ajithpeter3040]

Thank you ! :)

[@gregfeneis609]

3:11 I'm curious about the circuit construction. I bet there's an explanation for the orientation of the coils' winding axes. The lower 2 coil path has each at 90 degrees to the other, which would make sense to me. However, the upper path has the left and center coil approximately the same orientation and the right coil 90 degrees to the center. Does it matter, or is it just how it turned out?

[@w2aew]

It's largely just how it turned out, but it's a good idea to keep air coils not lined up in the same orientation order to prevent mutual coupling.

[@kd2eat]

Alan, does this kind of setup work in the opposite direction - IE two radios and one dual-band antenna? Does it attenuate the off-frequency stuff enough that one radio one damage the front-end of the other?

[@w2aew]

Michael Hojnowski In general, yes. But, you have to ensure that there is sufficient attenuation in the receive path. It will depend entirely on the diplexer design, and the transmit power.

[@vadzimdambrouski5211]

please make a video about duplexers, they sound interesting.

[@w2aew]

Next time I've got some cavity filters to play with, I'll definitely do a video.

[@keithwepking9988]

Hi Alan, will this diplexer be better than just using a Tee to connect two different antennas into a receiver only radio (scanner)? I'm using a 900mhz yagi & discone antenna connected with a Tee into a single coax cable to my receiver. I assume it will help with antenna/radio impedance.

[@w2aew]

It may help a little by potentially avoiding receiver overload and improving sensitivity a little, if the receiver is sensitive to the antenna impedance.

[@SoninbayarPS]

Can diplexer be used at the the Linear PA output with LPF to reduce heat of band LPF and stress of Amplifying device (LDMOS)?

[@w2aew]

No, that is not its purpose.

[@AJunior1969]

what power does it support?

[@fawwazal-subie2305]

Hi, thank you. I have a question: Can you receive and transmit using one antenna and attached that antenna to a Duplexer? I am confused as how the dipole can transmit and receive at the same time ? I appreciate your help

[@w2aew]

As long as the duplexer can provide sufficient isolation between the transmit and receive frequencies (so that the receiver doesn't get overloaded by the transmit signal), then it will work. This is commonly done with VHF/UHF radio repeater systems.

[@fawwazal-subie2305]

w2aew Okay. I guess my confusion is down to how the feedline handles simultaneously a coming and going signal. Would they collide ?

[@w2aew]

@@fawwazal-subie2305 The feedline doesn't care. All signals can be present on the feedline at the same time. Think about it this way, when you transmit out to your antenna, the antenna is still receiving signals and those signals are going down to the transmitter (which ignores them).

[@fawwazal-subie2305]

w2aew oh I see. I just was thinking like when the wavefront two opposite signals present on the same cable that they destroy each other.

[@0MoTheG]

Does the filter have to be high-Z T-structure? I have seen gear use 1:1 power splitter and then filters - sad but true.

[@w2aew]

0MoTheG There are a lot of ways to accomplish this function - some better than others...

[@backyardbasher]

i used to use one of these with a single dual band antenna (vhf/uhf) and separate vhf and uhf radios

[@w2aew]

backyardbasher Another good reason/need/use for these devices

[@alin936]

what is the diameter of the wire used for the coils ????

[@w2aew]

I used 21g, but the article specified 18g (AWG), but I didn't have any 18g...

[@MrTubbyToby]

Hey there, What kind of caps are those? Thanks, -KN4IWL

[@w2aew]

They're similar to these devices: www.digikey.com/product-detail/en/murata-electronics/TZ03P450E169B00/490-1952-ND/587973

[@tHaH4x0r]

Why would you use a single feedline for a different up and downlink antennas, i.e. why not use two different paths entirely? It seems to only have disadvantages...

[@nezbrun872]

It is not uncommon to have a full duplex cross band transceiver that only has a single RF port, but to use two different antennas

[@tHaH4x0r]

Nezbrun I think i need to rephrase my question. It is more in the likes of why would you design a transceiver that has a single RF port if you use two different antennas anyways, why not separate the two RF paths.

[@doncoltrane3565]

My IC-706 has only a single output for VHF/UHF. Further, unless you have unlimited wealth, using one piece of very expensive low loss feedline is another advantage.

[@w2aew]

Many (most?) multiband transcievers use a single RF port for many different bands. Multiband antennas are common. Rear panel space is also often at a premium. Many people operate FM satellites with an HT, which only have one RF port. Feed line is expensive, especially when you consider a long run up a tower, so running a single line makes sense. These are just some of the reasons why these devices are often used.

[@nezbrun872]

Don Coltrane Absolutely, at an extreme, I used to live in a basement and ran a single low loss heliax feed up to the flat roof seven storeys up, a 180' run in total. I ran HF through 13cm through the single feeder, with several diplexers at each end. I also had antenna mounted LNAs and PAs on the roof for VHF and above. Running individual feeders for each band would have been very expensive, not to mention drawing attention from the neighbours.

[@nickb2245]

Are the filters not direction sensitive?

[@w2aew]

No, they work exactly the same in either direction - so it can be used with a single feedline and two antennas, or a single antenna and two radios.

[@BalticLab]

***** Or two radios, two antennas and one feedline :)

[@sammin5764]

🌷🌟🌷

[@n2mpm]

So many toys.

[@karlacruzmaldonado7861]

hola

[@georgiosvergakis5666]

I was about to watch porn, but RF diplexer design theory distracted me.. ...these videos really get your attention, with those nice rf coils ,