[ARC5] [Milsurplus] MAAM World War II Weekend Report

[hwhall@aol.com]

Wonder if ahead of next year you could recruit an HF ham station or two (somewhere not very dependent on fortune & propagation) to spend the day standing by as your on-the-air contact.

Wayne
WB4OGM

On Wednesday, June 11, 2025 at 06:37:40 PM MDT, Mark K3MSB <mark.k3msb at gmail.com> wrote: 

Last weekend I spent 4 days at the Mid Atlantic Air Museum's World War II weekend as part of a regional reenactor group. Setup was Thursday with the event running Friday through Sunday.

This was my first time as part of a reenactor group.  It was very enjoyable and as I expected, I learned quite a bit from the  group.  The Military Aviation Museum had their full scale replica FW-190 and ME-262 at the event, and both flew!  Magnificent work!

Photos (including the FW-190 and ME-262):

www.k3msb.com/temp/reading1.jpg
www.k3msb.com/temp/reading2.jpg 
www.k3msb.com/temp/reading3.jpg  
www.k3msb.com/temp/reading4.jpg 
www.k3msb.com/temp/reading5.jpg

Objectives: 
Educate people on the HF radios used on Allied Bomber Aircraft in WW II.
Describe the differences between the Command and Liaison radios.
Demonstrate how a DF unit works.

Equipment used:
SCR-274N and DF Setup consisting of DU-1, an ATA CBY-46145 Broadcast Band Navigation Receiver, and a  BC-453 Beacon Band Navigation Receiver.
All the above were operational at the event.

What did I expect to happen:
Use the HF radios to talk to others at the event;  I also knew this might not happen.
Use the DU-1 and associated receiver to illustrate how an aircraft found it's position by the DF process.

What Happened:
There were no other active HF setups for me to communicate with using the SCR-274N.
Demo of the DF setup worked extremely well and was well received.

What went well and why:
The DF demo went well.  I had the ATA receiver tuned to an AM broadcast station about 50 miles away.   I explained how the operator would manually turn the DU-1 loop to find the maximum signal then report the bearing to the pilot (yes, I know they went for the null, but I didn't think that detail was relevant for my purposes).  I explained that the DU-1 loop was normally mounted on the fuselage with an extension shaft to the operator's table, and I showed them the scales the radio operator used to determine the bearing to the station.   I had an LP-21 Football next to the DU-1 for static display, and I explained that there was a loop inside the LP-21 that was motorized and worked the same way as the manual DU-1.    I then mentioned that two of the four C-47's parked behind our tents had these same Footballs; most people said they had no idea what they were for before my demo.    

I then mentioned that our equipment tent has a Gibson Girl and explained what it did, how it was used, and that downed crews were found using the same DF process from land bases or flying boats.  I explained these were examples of “Passive DF”.   I then explained how the SCR-247N could be used by a lost pilot to get a bearing to a known ground station by pushing the transmit button on the Transmitter Control Box in order for a ground station to give a pilot a bearing to the station.

I used a spare SCR-274N receiver dynamotor to power the DU-1 and associated receiver.  I explained what the dynamotor was for, converting 28V from the aircraft electrical bus to the 200 volts needed by the units.   I used a pair of 100 AH 12V LiFePO4 batteries in series to power the receiver and loop. 

Even though I did not use the SCR-274N on the air all the time, I explained the function of the command sets (short range air to ground / air to air)  and contrasted that to the function of the Liaison radios (long distance).  I showed them the inside of a command receiver as many of the younger people had never seen a vacuum tube.   I explained what each box did and how they could be located in different parts of the airplane, and what the pilot's receiver and transmitter control boxes did.

The SCR-247N was on 3885.  My antenna was a 45 foot wire that exited the Command Tent, went over the top and down the other side, then ran parallel to ground around the perimeter of the tent at a height of just over 6 feet.    Matching was accomplished by my custom box of a 4:1 UNUN and series matching capacitor and MFJ Tuner.   Matching was not a problem and I was able to get about 35 watts out of the transmitter on CW.  I don't know how much on AM, but I suspect less than 10 watts.   For initial testing, I disconnected the wire to the receiver and did a quick transmission of “B-24 on Final, go around....” or “This is B-24 Daisy Mae... we are going down”.   This illustrated the radios were indeed working.

The SCR-274N was powered by a (hidden) Astron 28V power supply with a pair of series connected tractor batteries across the output for initial current surge.  The group's generator was needed for running the unit.

I received quite a few surprised looks when I told folks the radios were 85 years and fully operational.

What can be improved and how?

There were no other reenactor groups on the field to talk to with the SCR-274N.  With the level of foot traffic in the radio tent, trying to find a station on 75 AM each time someone came into the tent is not practical.  Also, the group's generator needed to be running when I had the SCR-274N operating.   So, aside from the first few “we're going down” transmissions, the set was powered down.

A misconception I had was that I needed to be talking to someone (in general) on 75 AM to illustrate that SCR-274N worked.    What can also work is having a 2nd radio in the Command Tent.   This would require less power and a less efficient antenna.   I just need to talk across the tent,  not across the state.  The intent is to illustrate the radio works, not that I can work someone miles away.  Trying to always find someone to talk to would take time away from talking to visitors.

Another area for improvement is to use a BC-221.   I used a (hidden) digital frequency meter which is how I do it at home, but is obviously not how it was done in the field.    I need to get one of my 221's working.

Running the generator when it's hot can be an issue, along with the constant noise.  Replacing the dynamotor on the 274N with a pair of  batteries in series for the filaments and a 12V to 200V DC Setup Converter for HV are ideas to be considered.

Acquire at least one tuning cable for the SCR-274N.  I never had a need when using the command sets at home, but it would be an asset at an historical event.

Conclusion:

With the SCR-274N as basically display only, and a working DF setup, I had a steady stream of customers in the radio tent all 3 days.   Saturday morning, between 8:30 and just before 1 PM, was pretty much non stop show and tell!  

My setup was well received by young people.  I had kids turn the loop if they wanted to for a “hands on” experience.

A valuable lesson learned was that I do not have to be on the air in the normal sense to show the radios work;  finding someone on the air when people walk into the tent is not practical.   Having a second radio in the tent that I use, while letting guests use the SCR-274N mic,  would increase the user experience.

A humorous anecdote....  A short while after I gave my demo to a young couple (maybe late teens....) they came back and told me they had been in the C-47 behind me.  The C-47 had a lot of the radios I had but the tour guides had no idea what they did.   I thanked them and wandered over to the C-47 a while later and introduced myself.   The tour guide had “heard of me” and asked if I'd take some time to enlighten him about the aircraft's radios.  Well sure....  The aircraft had a BC-191 and BC-342N with an associated straight key, along with some (generically speaking) ARC-5 boxes.  No racks or mounts, and nothing was connected together.  I gave them a general rundown of what the radios did.  On the aft side of one of the bulkheads were a pair of BC-191 Tuning Units.  I told them they were used to change bands, but the tour guide wasn't understanding.  I asked permission to illustrate, and permission was given.  I undid the four clips and pulled out the tuning unit from the wall case – I thought the guy was going to have a heart attack!   He said “I thought those were part of the wall!”   I then showed him the tuning unit in the BC-191 and said you would pull that one out and replace it with the one I was holding.  I said it was like changing the band switch on a shortwave radio from AM to ShortWave – that finally clicked for him.  After replacing the tuning unit into the wall case, I turned around.... and there were about 10 people staring at me.... including the pilot.    I tipped my HBT cap and bid everyone a good afternoon.... no charge folks!

73 Mark K3MSB

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