[ARC5] MAAM World War II Weekend Report

[Mark K3MSB]

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
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://mailman.qth.net/pipermail/arc5/attachments/20250611/41b90973/attachment-0001.html>