Ham Radio - Measuring stuff with the Marconi modulation meter model 2305

[@Jimwill01]

Thumbs up for being informative. Doubt I'll ever be able to use it, but very nice to know! Thanks!

[@raccoonnyc]

Like your rf sampler hack.

[@SoddingaboutSi]

Mod N is the modulation frequency . I have one of these too quite useful for sig gen repairs.

[@rlmillr]

The audio filters are all important. Using the 300-3.4K filter would have made the measurement more accurate. With this in, it matched a calibrated HP8903B, without it it reads a little high. The 65 -250 is perfect for pl tones. Unfortunately the Sinad option was not installed but the LF output can be used to see gross distortion.

[@loughkb]

+rlmillr Good to know. Thanks.

[@rlmillr]

I also just noticed the freq, the 10Mhz looks like it is acting up unless the radio is really 1.6Khz off freq. I would check it with the other HP counter without modulation.

[@loughkb]

Nope, the baofeng is actually that far off. The Marconi had been on for an hour and I've been checking it before I use it. Both the HP and my Heathkit freq counters are within a couple of hrz of each other and they both saw the reference as being dead on.

[@m1cxzm0cnl92]

You have the same scope as me, I don't know if you know this, but that is a 200MHz scope that is limited by model numbers stored in a couple of files in the scopes operating system. All you have to do is connect a usb to serial cable ( the type used to program some arduino's ) to a pin header on the back of the board and change the model numbers contained within them using nano. As you are a linux guy this should be very basic stuff to you. The only other thing needed is to remove two surface mount capacitors to get the full 200MHz bandwidth which is just as simple as they are placed in a very easy location and easily identified. If you like I can link you to an article that fully explaines the proceedure. It takes about 10 mins to do and the hardes part is removing the two screws behind the handle. I did it to mine and am very happy with how simple it was and the results.

[@karlfell3768]

The MOD button allows you to read the frequency of the audio tone in the rf carrier. You forgot to demonstrate its RF power measurement capabilities as well as many other features the unit has. I have had mine for a couple of years now and I am still learning its capabilities. The hidden menus are a bit of a pain but worth learning. I use mine with a range of different attenuators and it is nice to be able to program in offsets to account for them. One of my favourite bits of test gear but I had to add deeper shelving to mount it, not a small unit. Great video, keep up the good work. Karl, M0KRL..

[@kd5inm]

Have you calibrated the Marconi Kevin?

[@loughkb]

+Off Grid Texas Homestead the person who sent it tuned the reference to a rubidium reference, so it's at least on frequency.

[@rlmillr]

If I remember it runs the self cal at every power on. W2AEW does have a nice video to check FM calibration that can be done without expensive equipment.

[@kd5inm]

I was thinking about if the Marconi gave a false reading if it was calibrated to a known source for modulation etc.

[@kd5inm]

referring to deviation measurements

[@loughkb]

It does a self-calibration upon startup. As long as the reference oscillator is on freq and producing a clean signal, it should be accurate.

[@cuban9splat]

Good stuff and interesting. Thank you. 73 DE K7RMJ

[@vidasvv]

Hello Kevin, I have one of these beauties, have you popped the covers off ? What a work of art ! My Wouxun KG-UV8D will deviate up to 11Kc sometimes when I key up. I used my spec an to verify this so your Marconi was most likely giving you an accurate reading. Thanks for uploading your video! Oh, how did you make your little T sampler ? 73 N8AUM

[@loughkb]

I took a standard BNC T and cut the pin in the center leg. You have to cut it right down to the plastic. It's tricky cutting in such a small place. I don't remember exactly how I did it!