Wednesday, December 25, 2019

Audio-technica BPHS-1 and Icom

I received a Audio-technica BPHS-1 headset for Christmas from my wife :-) The BPHS-1 looks to be a quality headset that is well rated on Amazon, Audio-technica's site and other places.

K8JHR wrote an article called Headsets I have tried, like or recommend which includes the BPHS-1.

I quickly discovered that Icom rigs (and Elecraft) are setup for electret condenser microphones, where as the rest use dynamic microphones. Electret mics are powered, dynamic mics are not and are about 20 dB lower in level. The BPHS-1 uses a dynamic mic.

Will a dynamic mic work with an Icom? Maybe..

Next, cables. The BPHS-1 comes with a cable that has a 1/4" plug for the headphones and a 3-pin XLRM-type connector for the mic.

  • First, the mic pin in an Icom supplies 8 VDC for the electret mics they use, when used with a dynamic mic we need to use a DC blocking capacitor otherwise the magic smoke will come out. Heil recommends a 1 uF tantalum (noted in link above), some posts on QRZ suggest anything up-to 10 uF is good. I found some 2.2 uF 16V tantalum capacitors on Amazon, these are polarized so the positive leg should connect to the mic pin in the Icom.
  • Mic side: Need a female 3-pin XLRM, I chose this cable from Amazon, can cut to length and wire into a 8-pin Foster mic plug with the DC blocking cap for the Icom's mic socket.
  • Headphone side: 1/4" to 3.5mm adapters are easy to find, thou I prefer a short cable here so the 3.5mm jack in the rig doesn't have an adapter and 1/4" plug hanging out of it. A quick search around Amazon finds MillSO 1/4 to 3.5mm Headphone Adapter, TRS 6.35mm Female to 3.5mm Male 1ft cable.
  • A cheaper option is to just cut the 1/4" and 3-pin XRLM plugs off, put a 3.5mm plug on the headphone side, and 8-pin Foster mic plug on the other plus the DC blocking cap.

Parts ordered, plan to have it together next week..

Parts arrived yesterday 29 Dec, I installed the DC blocking cap into the mic plug, I found I could fit it in-between the unused pins:

I cut the XLRM cable so it matched the 1/4" to 3.5 mm adapter cable length, and it looks like this:

Wiring diagram: Headset diagram from BPHS-1 manual (left), the mic connector diagram is from my Icom IC-7300 manual (right), with the connections shown as I wired it:

The shield (shown in green) I folded back in the mic plug and "clamped" in with the strain relief so it's grounded to the frame of the radio via the plug.

After adjusting the mic gain and compressor settings on SSB, I found mic gain at 80% and compressor at 5 would drive the IC-7300 about the same as the supplied hand mic with mic gain at 40% and compressor off. I did this by doing several comparisons watching the RF power output and listening to my self via the rigs monitor function with the headset on.

I have yet to do an on air test on SSB. I was able to do a quick test on a 6 m FM repeater, on FM the speech compressor option is unavailable and with the mic gain set to 100% the deviation is too low.

Sunday, December 22, 2019

AL-80B Keying Interface

KV5R wrote a nice article (Amp Interface) on building a solid state keying / relay interface for use with Icom rigs, using an SPST-NO MOSFET switch. I also have an Icom rig and an Ameritron AL-80B.

The nice thing about this is it's super simple, much faster than a mechanical relay and is opto-isolated.

I had ordered some parts for another project a while back, part of which was to rebuild the keying interface so I could key two devices. That project got shelved, but today I decided to rebuild the interface as originally planned since I had the stuff to do it.

Version 1 (with the heat shrink removed):

I had this hanging out the back of the rig, that was ok.

Version 2:

Only the orange and grey wires are used from the Icoms pigtail, the rest are just tucked out of the way.

The solid state switch's control voltage is 3 to 10V, but work ok from 12V. With two of them I wired them series for use with the rigs accessory jack which supplies 12V when keyed. With this I can independently key two separate devices with a closing current of 3A at up-to 60V each.

Parts I used:
  • Project box is a "Zulkit Waterproof Plastic Project Box ABS IP65 Electronic Junction box Enclosure Black 3.94 x 2.68 x 1.97 inch (100X68X50mm) (Pack of 2)", from Amazon. I have found it quite difficult to find good project boxes.
  • DIN plug and pigtail came with my IC-7300, I simply cable tied once for strain relief and a second time looping it through two small holes I drilled to stop the cable from rotating. This secured it nicely since I didn't have anything better on hand.
  • Solid state relay is a Crydom DMO063, Mouser part # 558-DMO063. Can also be found on Amazon, and other places.
  • Barrier Terminal Blocks TERMINAL STRIP 6 LUG, Mouser part # 158-1006.
  • RCA Phono Jack, Mouser part # 490-RCJ-032.

Monday, December 16, 2019

Ameritron AL-80B AM Operation

Since I get into a bit of AM on 75 m, I had wondered about using my AL-80B for some extra Amplitude Modulation power :-)

While chatting on 75 m AM today I raised the question about using an AL-80B on AM. A couple of the ops in the round table we had going said they work great, in-fact one who later joined-in was using an AL-80B!

Setting up an AL-80B for AM use is pretty simple, the goal is 100W unmodulated carrier power on AM from the amp.
  • With the Icom IC-7300 set to 30% / 30W on RTTY mode, tuned the amp, this delivered about 400W output.
  • Switching to AM I reduced the drive power (to 20% in my case) to where I got 100W unmodulated carrier power from the amp, modulated voice peaks are around 300W PEP.

With this configuration I found that anode would start to show a dull cherry red color after a few minutes of transmitting which is perfect for the 3-500Z tube.

Signal reports from the group indicated going to 100W carrier power made a worth while improvement over the 25W carrier / 100W PEP from the IC-7300 on AM.

The AM operators in the Pacific North West are a friendly bunch, if you enjoy informal round table QSOs that can last a while, then this is the place (3.870, 3.877 and 3.885 MHz).