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An inexpensive audio peaking device for the IC-7300



After working so many folks using an IC-7300, I decided to try one. Somewhat to my surprise, I really like it. As some have said, it is probably destined to become a classic - the 21st century equivalent of the TS-520.


I was pleasantly surprised at its audio quality on CW but do miss the audio peaking filters on my FT-DX10 and KX3. Fortunately, a simple and inexpensive resonant tube sitting on top of the rig makes the tuned signal “pop” out of the noise and helps to make up for the missing filter.


In an earlier blog entry I documented my experiments with external resonant speakers. One that I had built had a small speaker in a PVC base with a 2 inch “street 45 elbow” of PVC and a short piece of PVC. I took the speaker off and set the rest on top of the IC-7300 speaker grill and was surprised at how much difference it makes.


There is one drawback. To keep the size from being unwieldy, the resonant pitch frequency is higher than I would prefer. I found this configuration to work best at about 670Hz. I haven’t tried lengthening the piece of PVC in the elbow but from my earlier tests, I’m guessing it would have to be substantially longer to reduce the frequency significantly.


The PVC I used is marked 2” and the piece extending from the elbow is 2” long. You may want to start with a longer piece and shorten it to tune to the frequency you want. The most accurate way of tuning is sitting on your radio as it will be actually used. I used the “dB Meter” app on my iPhone and tuned through the pitch frequency while watching the for the peak.





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3 Comments


k4lxycw
Oct 04, 2023

A folded horn would definitely look nicer than my protruding tube. Have to be a little careful about blocking ventilation I suppose.

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mdoggllc
Oct 05, 2023
Replying to

I thought about that. The folded tube could lie flat on top of the box plenum that serves as the coupler to the speaker. Remember, the diameter of the tube has only a secondary effect on the resonance. So you could use a much smaller flexible tube (e.g. scrap vac cleaner hose or rubber drain hose). The folded tube could be constrained within the width of the speaker grille, and each loop could run front to back of the radio without impacting the ventilation grilles.


Another edit: seem like you could run a few loops side to side of the radio behind the speaker grille, with the tube input connected to the back of the plenum, and the output route…

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mdoggllc
Oct 04, 2023

Howard, you could try a folded horn. The "Bose" method. The resonant frequency is dependent mainly on the tube length, with a correction for the diameter (for open tubes). So, you could use a folded tube that lies flat on the top of the radio, with some kind of acoustic coupler (e.g. box with a hole in the side) between the speaker and tube entrance, Tuning method would be the same as what you are using.

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