To protect from close-talking "popping P's", a small white silk wind screen is mounted just in back of the mic opening with a 1/8th slice of foam behind it. I slightly enlarge the mic opening on the case and align the new element directly in back of it.
I added a shaped acoustic foam insert in the rear of the mic that helps deaden the circuit board and case (all studio mics use this). For mobile operation you will be using mic level settings under 25%! In the mobile, dial it down a bit, at home, bring it up a bit. Depending on your voice, you have the adjustment range to dial it right in now. Now, 50% puts you right at the sweet spot. It sounds like an excellent desk mic with tone adjusted just right.ġ00% mic level on the old mic is equal to 25% mic level on the new element. This results in more understandable audio on SSB. We've boosted the highs and trimmed the bass - shifting the center of the audio energy spectrum up. Mic level settings on SSB will be much lower than the old mic element (from increased drive). This makes the ALC go nearly to the end of the bar. (especially on simplex)įor SSB, my favorite setting is 50% mic level with 200hz on the TBW low setting, 2900hz on the high. With the stock mic, I got continuous reports of low audio on FM.
Now it easily goes out to full deviation with average speaking levels (15KHZ filter setting / 50% mic level). The new setup also gives FM a brighter - cleaner sound. Set the TBW to 300/2500 and you have that pile-up busting sound. TBW at 200-2900 is perfect for regular QSO's. I left just enough bass at the low end to sound really great at the "Wide" SSB setting. With the custom element and changed SMD coupler cap, I obtained a smooth balanced response and the optimum drive level.
With my combinations of mods, that's exactly what this upgrade does. FM and AM needed much more drive to function correctly. My goal was to have the option of nice clean audio for rag chewing and then using the rig's TBW to tighten it up for DX chasing. I contacted a small US manufacturer of mic elements and they agreed to make a custom element to my specifications (with a significant minimum order) My specs were definitely non-standard. I realized that these elements were made for consumer electronics and not radio mics. I obtained and tried dozens of elements from the big parts suppliers. Finding that specific point took a lot of experimentation. I had to find the compromise between FM and SSB drive requirements. Feeding the DSP Codec excess audio in the bass range just uses up valuable bits - and doesn't land up representing sound that enhances understandability.
The technical goal is to find a balance between driving the 1st audio op-amp in the rig so that it is nice and linear - and having that deliver a signal to the DSP which is what it wants to see.so as to produce the best signal the rig is capable of. It's a better idea to upgrade the 151 and keep all that remote functionality, rather than using another type mic which doesn't have the remote controls. You can't even access the stacked VFO registers unless you use the 151's buttons. I find I actually use the function buttons on the HM-151. There is also a bit of hollow-ness from the mostly empty plastic mic housing. This would require a change of the surface-mount blocking capacitor on the mic's circuit board.
Being the original mic element is a condenser-type, the replacement would also have to be condenser. I realized that the mic element had to be changed. None of them really made it sound like it should. I tried all the obvious quick-fixes on my HM-151 mic.