D-104 microphone and the Collins KWM-2

[K4FY]

I have been using a D-104 (chrome lollypop) microphone with a T-UG8 stand with my KWM-2 for a while. In its original condition, the mike and stand are configured for push to talk, not VOX. All that’s need put the mike in VOX mode is to not wire the PTT switch to the XCVR mike jack and put the PTT lever permanently on. This un-shorts the D-104 element and activates the built in amplifier.

The D-104 has a rising response at the high end. Old marketing sheets claimed an increase in intelligibility and “punch,” much like Heil does for its “DX tailored” headsets. This caused some concern how this response curve, along with the T-UG8 amplified stand, would play with the Collins gear which historically favored EV-638, Turner or similar products.

One Ham site recommend setting mike gain on the KWM-2 to 10 O’clock then advancing the T-UG8 gain pot until The ALC averaged around S-6 to S-8 as suggested by Collins. The results have been interesting, because several Hams have indicated that the D‑104/KWM-2 combination is best avoided.

The KWM-2 runs barefoot into a 40-20-10 dipole designed using the EZNEC program. SWR runs roughly 2:1 across all bands. The antenna is 35-40 feet high. Using this modest combination to enter a few small pileups and invariably resulted in a contact, sometimes the first in line. Then there were unsolicited audio reports. Some recent comments included, “you’re running S-6 on the meter but your audio sounds like S-9 or higher.” “Very good audio.” “Audio really punches through.”

These results may not be typical, much less predictive, but I thought they were interesting.

73,
Gary, K4FY

[W0BTU]

The D-104 has a rising response at the high end. Old marketing sheets claimed an increase in intelligibility and “punch,” ... Then there were unsolicited audio reports. Some recent comments included, “you’re running S-6 on the meter but your audio sounds like S-9 or higher.” “Very good audio.” “Audio really punches through.”

As you've already learned from those unsolicited audio reports, those old marketing sheets were telling the truth, and not just a bunch of hype. There's a lot to be said for the D-104 and microphones with similar audio characteristics. I wrote an article about this that you may be interested in at http://www.w0btu.com/ssb_audio-weak_signal.html .

We can sometimes accomplish the same thing at 100 watts with the right audio as we can at 1500 watts with an "ordinary" microphone. :-)

I personally don't like the design or appearance of a D-104, but after countless hours of testing different microphones under weak signal conditions, I wouldn't have any other microphone for that purpose.

[K9STH]

The Astatic D-104 microphone was continuously manufactured from the early 1930s until just a few years ago. There are a LOT of D-104 microphones used on Collins transmitters.

As for VOX: It is almost impossible to get the VOX timing correct. Using VOX the first sylable of the transmission is cut off. Then, if you don't talk fast the VOX "drops out" or, if the delay is set too long, the transmitter stays "on" too long! That is why a LOT of people using VOX operation have a LOT of "ahhhs" and "ummms" during their transmissions to keep the VOX from dropping out!

With the preamplifier, you need to use the switch on the microphone or else the 9-volt battery goes down really fast. Some people add a switch to their D-104 microphones to remove battery voltage when the microphone is not in use. Of course, it is very possible to forget the switch and leave it in the "on" position!

I don't use the microphone jacks on any of my S-Line equipment or on my Heath SB-Line equipment. On the rear chassis of all the S-Line and KWM-2- series equipment there are RCA phono jacks for both PTT and "Phone Patch". The "Phone Patch" jack is in parallel with the microphone audio from the microphone jack as is the PTT connection. I have modified all my Heath SB-Line equipment to add a PTT jack. In the Heath equipment the "Phone Patch" connection is already in parallel with the microphone audio connection on the front of the units. By using the phono jacks on the back of the equipment I don't have to worry about having microphone plugs extending from the front panels.

Using a foot switch for PTT works wonders for phone operation. Both hands are free to do other things (like logging, computer operation, etc.) and you don't have to worry about the VOX dropping out. Just use your foot to key the transmitter and let it off just as soon as you are done talking. I even use the foot pedal for CW because of the basically instant time to go between transmitting and receiving.

I do have a "patch panel" so that my microphone can be switched between each of my transmitters. I do use a rotary switch for the PTT so that the foot pedal can be used on all the equipment.

Also, my D-104 (which I don't use that much) has a switch added so that the microphone element can either go straight through to the transmitter or go through the preamplifier. For everyday operation from my main console, I use a microphone on a "goose neck". But, I definitely use the D-104 at my Heath "original" twins station. The patch panel for the microphone connections is just above the 75S-3A in the second photograph at

http://k9sth.com/uploads/Equipment_a...March_2012.pdf

Glen, K9STH

[W0BTU]

The Astatic D-104 microphone was continuously manufactured from the early 1930s until just a few years ago.

There's a very good reason for that. They were --and still are-- hard to beat for their audio characteristics, whether you were operating AM or SSB. Not only do they sound crystal clear, but they are almost unsurpassed for weak signal work.

There are a LOT of D-104 microphones used on Collins transmitters.

Yes, and on countless other brands of equipment, too. The D-104 even beat the ones that Collins sold as a so-called "matching" mic. The D-104 was a heck of a lot better match.

As for VOX: It is almost impossible to get the VOX timing correct. Using VOX the first sylable of the transmission is cut off. Then, if you don't talk fast the VOX "drops out" or, if the delay is set too long, the transmitter stays "on" too long! That is why a LOT of people using VOX operation have a LOT of "ahhhs" and "ummms" during their transmissions to keep the VOX from dropping out!

That's for sure. Maybe there are some rigs out there that have better VOX, but nothing I've ever owned had VOX that didn't do at least some of what you describe above. Probably, the people we hear that don't seem to have these issues are using a foot or hand switch.

With the preamplifier, ...

I've always been tempted to try the 8 volts that's available at my IC-765's mic jack to power my D-104's preamp, but I never have.

... http://k9sth.com/uploads/Equipment_a...March_2012.pdf

Looks good, Glen!

Although I will certainly regret doing it someday, the first person who offers me the right price (probably more than it's worth) for my S/Line can have it. It's just taking up space that I need for other things. I've had my fun out of it since 1979, and it doesn't have the features or bands I enjoy on the IC-765.