2m Low Pass Filter for Ham Radio 

Thanks for another good video, I don’t understand everything you talk about in your videos but I always learn something.

Fun. If you do it again, you might check SWR of the filter on a VNA. It should be good, but you never know.

You might check out what I did working as a co-op engineering student at a USAF radar site. With multi-megawatts of RF floating around, I worried that the two-meter transceiver in my car might get fried. I made a quarter-wave (corrected for the velocity factor) coax stub shorted at the end. It gave me no problems on receive or transmit, but it was a dead short for even multiples of 145 MHz and a partial short at other frequencies. It's easy and costs almost nothing. It is also a good way to kill that second harmonic on those cheap Chinese hand-helds.

Interesting experiment, but that proto board will introduce a significant amount of capacitance to your circuit. In addition, keeping your capacitor leads so long will add inductance in series, creating tuned circuits. Despite the limitations of your setup, I applaud your experiment and your video. This is the type of experimentation that will make ham radio a great training ground for competent, trained radio operators. Congratulations!

I've built my own filters using that exact website. It's a brilliant tool. Chebyshev filters *add* passband ripple in order to have a steeper rolloff. Butterworth filters have no ripple but will rolloff slower and give less suppression on the harmonics (which you could compensate with 5th order for example). It's all a compromise.

Nice filter experiment. I think I have one of those NanoVNA test board kits around here someplace. Man, that radio is really bad when your filter could not knock down the spurs!

Great video and thanks for sharing the mark microwave resource. Keep on keeping on, brother Ape!

Dammit Ape, I ain't got time to get interested in filter design... Looks fun, well at least you made it look fun

Good presentation!

Great video Mr Ape

You're learning fast. You'll be a good RU-vid Elmer, and RU-vid desperately needs good Elmers. Now try a closer-wound inductor with fewer turns. That will reduce the loss of the filter.

At least the Talkpod is good for something! Cool to see that test.

Hi Ape, Very good experiment that actually worked. If you can't steepen the curve, maybe another stage of filtering. I've seen Chebyshev filters with 3 and more stages. Stay safe. 73 WJ3U

Pretty nice!

nice. I meant to fiddle with my test board a while back. Would be fun to have the smt version of this with a little easy bake wave solder oven.

Very interesting 😊

@TheSmokinApe Simulation of the circuit with the values from Marki's filter calculator does not show the insertion loss peaking at 300 MHz, then increasing response above that. The loss should continue to drop, out to infinity. One of the culprits is almost certainly excessive lead length of the capacitors. I guesstimated the inductance of the leads and the test boards at around 15 nH for each capacitor, and simulation with that value puts the dip in response at around 300 MHz, just as your filter shows. You can find air core inductor calculators on the web, you'll probably have to try several to find one you like. I guesstimated the dimensions of your inductor and added the guesstimated inductance of the leads and the inductance you have should be in the right ballpark. Your measurement of 2.4:1 SWR is suspect, just doesn't feel right with the rest of your measurements at and near the design cutoff. I would build another filter without using the NanoVNA TestBoard. Too much stray inductance and capacitance for any serious work with those. Just solder a couple of SMA edge connectors to a piece of double sided PC board of appropriate width - just enough to fit your inductor between them, maybe .6" to .75" - then solder the inductor in. Then solder in the caps with the body of the cap practically laying on the PCB, leaving (damn near) zero lead length, and solder the other lead of the cap with the body of the cap practically up against the inductor/connector junction, again with (damn near) zero lead length. Now, sweep that sucker! I have built circuits like that for operation well above 2 meters, well into the gigahertz range. Another suggestion: those capacitor kits. Who made the capacitors? Some of those kits are OK, some of them barely earn the rating of "junk." Murata and Panasonic have always made top notch capacitors, Vishay is also good as high as I have tested them (low VHF). There are several others, but they don't make a lot of leaded capacitors, mostly surface mount. And they probably don't make kits. Life is getting harder for hobbyists and experimenters. If you don't know how to check caps at VHF and up with a VNA, learn how, and test the caps you've got. If they don't perform, well, at least you can use the boxes to put good capacitors in. Buy them from Mouser and Digikey or other reliable vendor.

I told you I was going to watch… neat project☑️

great project . to bad the prototype board is small. to clean up more you would need more sections . but doing that you will get more insertion loss . Sota beams has a 2 meter bandpass filter . the down side is have to take it out to use 70 cm. 73's

Regarding the A36 CPS, there is a column heading for “Signaling.” From the factory, some frequencies were set at 5 and some at 1. What is this and what should the values be set at for simplex and repeater operations. Thanks!

Theres not too much in this filter. Nice kit to do some testing Mr Primate. That radio is dirtier than your red headed cousin but you got her in rehab, work in progress.😂👍

Hi Ape. Every filter hobbyist knows the problem with the exact capacitor values. I would have built the filter into a shielded sleeve that could be plugged onto the radio and measured the harmonics at a distance of around 20 meters with the Tiny SA antenna and this in the open field.

I wish I had watched this before I started trying to make a broadcast filter for my SDR. I was expecting to just follow a plan and tune it up a bit but I learned the long way about the Nth order versions being necessary for stronger interference. Also what do you look for in a capacitor assortment like that assuming they will just be used for filters and filters disguised as other things like band traps? I inherited a whole shack of random parts from an SK so I haven't had to buy many capacitors yet but it would be nice to not have to search through his unlabeled boxes of jumbled 1960s capacitors to find what I need assuming he didn't use all of whatever I'm looking for :)

Nice job on the filter, I guess on a better radio it should clean it up!

fun video

Need Help ! Im doing satellites contact , and in FM everything is allright . But i just bought 2 Yaesu Ft817 and im trying SSB satellites . The thing is , when i transmmit on 2M the receiver on the 70cm side is 100% overloaded by the near by transmitter . Do i need a low pass on 2M or a high pass on 70cm , or both ? Im using an Arrow dual band yagi with 2 separate coax , connector and radio . Thank you and 73 ! VE2XXQ FN46rx

You are testing TX mode, will this work as RX also?

👍

Man i really wish those radios were better. I want the clear case😂

Have you tried a bpf? Another section or look for higher Q using same network. Great video! 73' de K4WRF

Great video! Have always believed that this would be a great project for all those dirty 💩💩💩💩 Baofengs!! 😝😝😝 73 de VK2AOE

cyan is a light blue colour 😂

I forgot just how dirty that radio transmits! It is a shame the manufacturer either didn't test for spectral purity or didn't care that it was out of spec. Neither is acceptable.

What I find amazing is the manufacturer was too cheap to add 2 capacitors and a coiled piece of wire to their output. 🤔🇨🇦

"capacitor shunt to ground" 🫢🫢🫢