Crystal/module questions for PCM radio

[falkin8er]

Hi all, I recently picked up a vintage Futaba Magnum 1024 FP-T3PB PCM radio. I just had a few questions regarding crystals and module regarding this radio. Is someone able to help me out with these?

- Do I get single or dual conversion crystals for the transmitter & receiver (receiver is a PCM 1024 FP-R113iP)? What exactly is the difference between single & dual conversion?
- On the box, it says channel 76 (75.710 MHz). But it didn't come with crystals - I'm assuming I can put in any crystal frequency in the 75 MHz band?
- I've seen some things online about it being against FCC regulations to change the transmitter frequency if you're not a certified technican, but this can't be true, right? People chance the frequency all the time, right (as long as it stays within 75 MHz band)?
- The module that came with the unit is FP-TL-FM, but I'm looking to get some extra modules and saw someone listed a FP-PK-FM module - does anyone know if that would be compatible with this radio?

Thanks in advance for the help!

[Elkcycles]

You can swap channel crystals from 76 to whichever you have on hand. You are not breaking FCV regulations by doing so. Additionally, any Futaba surface module will work in the PCM 1024. I have used the 27mhz AM module, FASST module, and a converted KO Propo ASF module without issue. I'd stick with Futaba surface crystal sets, but have used Hitec and Airtronics/Sanwa AM crystals as well.

[Frankentruck]

I picked up one as well and a separate receiver. The module has a TX crystal in it, covered be a square aluminum sticker. Mine has a Futaba type 72-7 crystal. I have a same frequency 72-2 RX crystal purchased but not in hand yet.
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[falkin8er]

Thanks Elkcycles. My only remaining question is whether I should get single conversion or dual conversion crystals. From what I can tell, it seems that the FP-R113iP receiver would require single conversion crystals, but I can't confirm this. Do you happen to know?

[juicedcoupe]

Since it was on channel 76, I'd stick with channels in the upper range.

From what I remember, the receivers were calibrated to work best in upper and lower ranges of 75mhz. I'd probably stay above channel 60, maybe 70.

[falkin8er]

Thanks juicedcoupe. Do you know if I need to get single or double conversion crystals?

[RC10th]

If you can find a spektrum module for it you can use 2.4 unless you want to keep it original.

[Frankentruck]

Type 72-7 RX crystal arrived and works great with this receiver and my FP-T3PB PCM 1024 radio.
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[falkin8er]

Frankentruck where did you get this from? Is this single conversion? Do they sell pairs that also come with the TX crystal?

[Frankentruck]

I got it from eBay. There is a set of type 72-7 crystals listed. I don't know anything about dual conversion other than I see some airplane radios use it.
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[nontrucker101]

While this is a older post, they still show up in a search. the OP had a few questions and comments.. so I'll try to be helpful.
" Do I get single or dual conversion crystals for the transmitter & receiver (receiver is a PCM 1024 FP-R113iP)? What exactly is the difference between single & dual conversion?"
First off, the Tx crystal and Rx crystals have slightly different jobs. The one in the TX is the basis for the transmitted frequency. And thru amplification, it becomes the active radiated signal. Several circuits are tuned to the exact frequency being transmitted. The reason a end user isn't allowed, is because without a spectrum analyzer and frequency counter, there is no simple way that a person can re-align the TX properly. Will it work if you replace one with another that is close in frequency? That helps, but spurious emissions can occur, and your TX may splatter over into the next channel, causing interference. If your radio has TX modules, THOSE can be chanced because each one is tuned properly to the included crystal.

As for RX crystals, there are differences.. several actually. If a Rx is single conversion, that means a crystal is chosen that is above or below the desired frequency by an amount called the IF (Intermediate Frequency), and that "mixes" with the incoming radio signals (of all sorts.. ) into a tuned circuit, that begins to exclude the unwanted. When the two signals mix, out of that you get both originals and the sum, and the difference. If it's dual conversion, the first IF is 10.7 Mhz typically.. if single, then its 455kHz. But they run thru more amps and filters, which cause the receiver to be more selective, and sensitive. So a SC receiver is good, a DC is better.

Most receivers are designed to take crystals different from original. The aircraft band has 50.. so one end is High, the other is Low. You want to keep a Low receiver on the lower crystals. The 75 MHz band for surface vehicles, STARTS are 61.. so the later posted comment about that, is actually referencing the top Aircraft channel. I hope that helps to clarify somewhat.

- On the box, it says channel 76 (75.710 MHz). But it didn't come with crystals - I'm assuming I can put in any crystal frequency in the 75 MHz band?
- I've seen some things online about it being against FCC regulations to change the transmitter frequency if you're not a certified technican, but this can't be true, right? People chance the frequency all the time, right (as long as it stays within 75 MHz band)?

[gtv1]

If you can find a spektrum module for it you can use 2.4 unless you want to keep it original.

Thats what I have done with me Fut 3VCS. love this radio and now its 2.4 its brought it back to life.
The only problem is I have to use DSM rx only which are getting harder to find.