[MRCA] Fwd: CR-1 crystals for an RT53B/TRC-7 RT
Tim
timsamm at gmail.com
Sat Oct 4 14:07:34 EDT 2025
Hi Mark - Regarding VHF ground-air antennas, simple might work OK. Some
related experience:
Awhile ago we ran a local net on 145.45 AM with an A.R.C. Type 12 on the
mountain (2500' AMSL), simple 5/8 whip. We had 2 USMC/MAW transceivers on
freq at ranges of 17 and 27 miles respectively, optical LOS. One MAW was
running the issued chassis-mounted whip and the other with the issued
ground plane configuration on a short mast, both "by the book".
Propagation and system-wise the comms were excellent despite the MAW's
somewhat deaf receivers and appx. 1 watt transmitters. (High ground is your
friend!)
(Some details on the Type 12/system used in these tests:
https://www.n6cc.com/a-r-c-type-12-vhf-am-aircraft-system/ )
(So for your proposed Op and vehicle an MAW would also be period-correct if
you have issues with the TRC-7. And of course FCC/FAA type acceptance
legality issues as others have noted in the aircraft band. The crystal
issues between the TRC-7 and MAW are probably identical (the MAW's used
8025 kc (18X) for 2 meters, FT-243's.) Both MAW and TRC-7 have 12 mc IF's
so the RX crystals should be the same. Just some alternative ideas). That
TRC-7 is interesting. I wonder how often they were used for G/A comms in
WWII.
Have fun with your Op, would love to be able to be there!
Tim
N6CC
On Sat, Oct 4, 2025 at 7:43 AM Edward Larsen <ki6rcm98 at gmail.com> wrote:
>
> Mark,
> You could try to find an original antenna for the TRC-7 and connect it
> to the handheld radio. The antenna would be period correct. One could
> also copy/build the antenna and paint it green. The antenna should be set
> up in the clear, above the test for best coverage. This would work far
> better than a rubber ducky antenna.
> 73
> Ed, KI6R
>
>
> ---------- Forwarded message ---------
> From: MARK DORNEY <mkdorney at aol.com>
> Date: Sat, Oct 4, 2025 at 5:59 AM
> Subject: Re: [MRCA] CR-1 crystals for an RT53B/TRC-7 RT
> To: Edward Larsen <ki6rcm98 at gmail.com>
>
>
> Hello Everybody,
> Thank you for all the very helpful information. Here’s the
> backstory.
>
> At a recent commemoration ceremony, we had a flyover by a WW2 warbird.
> The warbird was supposed to be coordinated to fly over at a specific time
> during the ceremony. Coordinators had a modern handheld radio with a
> “rubber Duck” antenna for use at the ceremony site to be used to
> communicate with the aircraft to help insure that coordination. The
> frequency they use for admin stuff when working the aircraft is 130.30 MHz.
> My WC-52 was at the site, in town, with a red panel marker draped on the
> roof in the hope that it would aid the crew of the aircraft in spotting us
> on the ground. The aircraft had GPS navigation onboard, which did enable it
> to fly directly over the site of the ceremony. The timing, however, was a
> bit off. Comms using the handheld were sketchy at best - basically, we
> could not communicate with the aircraft. Short range radio with a rubber
> duck antenna ( great for close in stuff, not so good for comms with an
> aircraft in the air, since the aircraft would only be in range for a minute
> or two). The crew were also not able to pick out the bright red panel
> marker we had on the ground, since the ceremony site was in town, and the
> crew were not able to pick it out of all the ground clutter. The HF set I
> have in the WC ( BC-654-A ) was useless for this operation, since the
> aircraft was not equipped with HF radios.
>
> So how to fix this? We either come up with an HF set for the aircraft (
> not happening) or we come up with a VHF set on the ground, set to an admin
> frequency ( there was no need for us to talk to a control tower or
> chit-chat a lot with a bunch of other folks in the air). So we started
> exploring options for a ground radio better than a handheld with a rubber
> duck. Well, anything that gets installed in the WC has to be WW2 vintage,
> and has to work. Power supply is 12 volt DC, supplied by the vehicle (
> typical for WW2 vehicles modified for use as radio vehicles ). The TRC-7
> uses the same battery as the SCR-300/BC-1000 radio ( BA-30) . I have two
> power supplies for the BC-1000: one is an older civilian vibrator power
> supply designed to use a 6 volt battery - make a holder for the 6 volt
> battery, and the vibrator power supply and configuration is basically the
> same as the original design ( manpack portable). I also have a WW2 issue
> PP-114, which is the vehicle mounted power supply for the SCR-300/BC-1000
> that is used when that radio is mounted on a vehicle ( one use was a US
> Locust tank - replaces the BA-30 battery). No modification to the radio
> is needed to use either one of the power supplies. While a WW2 era radio
> not the best option for this job, the TRC-7 in the WC really is the only
> option for a working WW2 ground forces VHF set in the WC. I’m not too
> enthusiastic about putting a VHF set in the WC, but it is what it is.
>
> The third (best) option is for the group doing these ceremonies to set
> up a better modern air frequency radio that uses something better than a
> rubber duck antenna, and if they had to, set it up on the a spot at the
> ceremony site not accessible or really seen ( like in a tent) by the
> general public if they want the best chance to actually talk with an
> aircrew in the air. Either build a better antenna that can be used with the
> handheld to replace the rubber duck, or buy a better radio with a better
> antenna. An antenna is an antenna to the general public- to most just about
> any antenna wouldn’t be seen as being out of place. So far, these two
> options have not been met with a lot of enthusiasm.
>
> Mark D.
> WW2RDO
>
>
> “In matters of style, float with the current. In matters of Principle,
> stand like a rock. “. - Thomas Jefferson
>
> Sent from my iPhone
>
> On Oct 3, 2025, at 10:23 PM, Edward Larsen <ki6rcm98 at gmail.com> wrote:
>
>
> Mark,
> You have a worthy project. Some of the old WW2 era equipment is
> fascinating in both design and function.
> I looked through my junk box. I have the transmit crystal in an FT-243
> package. It tests at 7238.709 kHz in my crystal tester. It would likely
> adjust to the needed 7238.888. You would need to attach it to CR-1A case
> pins, which are larger.
> I don't have a receive crystal, but there may be options. The receive
> crystal oscillator uses a dual triode tube, with one triode as a
> fundamental oscillator, and the second triode as a multiplier. This means
> you may be able to use a crystal frequency at a non-recommended harmonic
> ratio in the 11x to 17x range and still get the harmonic generator to
> tune-up. The oscillator circuit may need some slight modification if
> either the fundamental or harmonic tune-up doesn't work correctly.
> Other possible receive crystal frequencies
> Harmonic - Frequency
> 17 - 6976.470 kHz
> 16 - 7412.500
> 15 - 7906.667
> 14 - 8471.428 (desired multiple)
> 13 - 9123.077
>
> I have a 6961.025 kHz in a CR-1B case. I doubt the oscillator circuit
> could be tuned to 6976.470. One could try to disassemble the crystal and
> carefully polish the quartz wafer to raise frequency about 15.4 kHz. In
> the old days hams often did this.
> I have I have 7407.671 kHz in FT-243 case. This would need to be
> raised about 4.8 kHz. There is some chance the oscillator circuit could be
> tuned or modified to move the crystal this far without a quartz wafer
> polish.
> Lastly, I have 8450.121 kHz in FT-243 case. It would need to be
> lowered about 21.3 kHz by oscillator circuit adjustment. I doubt the
> crystal could be pulled this far.
> I would be very careful putting that old transmitter on-the-air. It
> won't meet FCC specs for spectral purity, harmonics or other spurious
> radiation. It may interfere with others in the VHF/UHF bands.
> Let me know if you need any of these crystals. You can have them for
> shipping/packaging cost, or simply send me a shipping envelope and I'll
> send them to you. Let me know what you want to do.
> 73
> Ed, KI6R
> SaddleBrooke, Az 85739
>
>
>
> ---------- Forwarded message ---------
> From: Edward Larsen <ki6rcm98 at gmail.com>
> Date: Fri, Oct 3, 2025 at 4:27 PM
> Subject: Re: [MRCA] CR-1 crystals for an RT53B/TRC-7 RT
> To: MARK DORNEY <mkdorney at aol.com>
>
>
> Hello Mark,
> I found the manual at archive.org. It looks like the transmit LO
> multiplies by 18, thus the transmit crystal for 130.3 MHz would be
> 7.2388888 MHz.
> The receive IF is 12 MHz and it uses low side LO, thus the receive LO
> frequency for 130.3 MHz is 118.3 MHz.
> The receive LO is an odd arrangement of a harmonic generator followed
> by an amplifier that is tuned to multiply from 11 to 17 times. The receive
> crystal must be in the 8.00 to 8.47 MHz range. The needed harmonic in the
> range of 11x to 17x is calculated. I calculate 8.4714285 MHz for the
> receive crystal using the 14th harmonic.
> I'll check my crystals to see if I have any of these. I will be
> surprised if I do. I'll let you know.
> Tuning the unit will be a little tricky. One will need to know how to
> tune the harmonic generator in the receive LO, to the correct (14th)
> harmonic. The electronics technicians back in the 40s knew their stuff.
> They likely used wave-meters or grid-dip meters to verify the correct
> harmonic.
> Ed
>
> For 130.3 MHz TX/RX:
> TX crystal: 7.2388888 MHz
>
> RX crystal: 8.4714285 MHz
>
> On Fri, Oct 3, 2025 at 2:47 PM MARK DORNEY <mkdorney at aol.com> wrote:
>
>> Hello Ed.
>> Looking to set up 130.30 MHz. Thanks.
>>
>> 73
>>
>> Mark D.
>> WW2RDO
>>
>> “In matters of style, float with the current. In matters of Principle,
>> stand like a rock. “. - Thomas Jefferson
>>
>> Sent from my iPhone
>>
>> On Oct 3, 2025, at 11:14 AM, Edward Larsen <ki6rcm98 at gmail.com> wrote:
>>
>>
>> Mark,
>> I have some CR-1A crystals. What fundamental frequency do you need?
>> Ed
>> KI6R, Az
>>
>> On Thu, Oct 2, 2025 at 7:32 PM Jason WA6BBQ <w6iee.73 at gmail.com> wrote:
>>
>>> Look into qrp-labs.com ProgRock2. It’s actually a synthesizer that
>>> runs off of 5 volts.
>>>
>>> I modified a TRC-77 with two of them, and it works super, easily gives
>>> me 6 transmit and 6 receive frequencies , and I can change the T/R
>>> frequencies at will.
>>>
>>> It will take a little work to adapt to your application, but still
>>> easier and vastly cheaper than unobtainium xtals.
>>>
>>> Unfortunately, it’s a British company that ships from somewhere in
>>> Turkey, so you will be paying some tariffs and related fees.
>>>
>>> Jason WA6BBQ
>>>
>>> On Thu, Oct 2, 2025 at 16:50 MARK DORNEY via MRCA <mrca at mailman.qth.net>
>>> wrote:
>>>
>>>> *From:* MARK DORNEY <mkdorney at aol.com>
>>>> *Date:* October 2, 2025 at 5:42:03 PM EDT
>>>> *To:* mailman at mrca.qth.net
>>>> *Subject:* *CR-1 crystals for an RT53B/TRC-7 RT*
>>>>
>>>> Hello Everybody,
>>>> I’m putting together an RT53B/TRC-7 VHF RT. The one frequency of
>>>> real interest is 130.30 MHz ( the set is to be used when a real WW2 C-47 is
>>>> dropping supplies/paratroops at events). There hasn’t been a decision on
>>>> what second frequency is to be installed. The Crystal holders are the CR-1.
>>>> Looking for the crystal holders and a somebody that cuts custom crystals?
>>>> Any help is appreciated
>>>>
>>>> Mark D.
>>>> WW2RDO
>>>>
>>>> “In matters of style, float with the current. In matters of Principle,
>>>> stand like a rock. “. - Thomas Jefferson
>>>>
>>>> Sent from my iPhone
>>>> ______________________________________________________________
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