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Old 07-19-2004, 08:25 PM   #1
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Default Dual Conversion? Short Crystal Only? -- Need Rx Help --

I currently have a Futaba T3PDF (75Mhz FM) Tx and a Hitec HFS-03MM Rx. I am adding a car to the "fleet", so I am looking for a Rx for it. I can't find the HFS-03MM anywhere. Tower Hobbies lists a Hitec DCX Rx, but it is "Dual Conversion", and appears to require "Dual Conversion" crystals.

1 - what does "Dual Conversion" mean?
2 - will "normal" crystals work with this Rx?

Futaba has an R133F, but is says that it has to have "Short Crystals"

Related Question - the reason I want the third channel is just to power a personal transponder (ordered, not here yet). Am I correct that I need an available channel on the Rx to power it - or a "y" cable...??..

I need a RX soon - I want to run the new car this weekend, but not bad enough to swap Rx's between cars every heat....
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Old 07-19-2004, 09:38 PM   #2
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About the Y cable, it depends if you run nitro or electric. If you run nitro, you will either have to get a 3ch rx or a Y cable. But if you run electric, you can just plug it into the battery slot on the rx. I've done this forever and it works.

I believe dual conversion is like if I run 88 and you run 89, there will be less glitching than with single conversion. I heard that somewhere and don't know if it's true.
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Old 07-19-2004, 09:42 PM   #3
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I am running electric, so the "Batt" slot is available.. I didn't know if that would work since that would be a voltage "input" to the RX, and in this case it needs to be a voltage "output".

Been a lot of views to this thread tonight, but no responses about what RX will work. I hate to think that my current crystals and/or radio are obsolete....
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Old 07-20-2004, 09:54 AM   #4
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No help for the receiver dummy?

I probably won't be able to find a RX and have it delivered by this weekend - even if I do find out the differences... Don't guess the mini will get to run Saturday.
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Old 07-20-2004, 04:52 PM   #5
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I use a DCX, and I think it's an excellent receiver, with less glitching than a single conversion. The downside is that you do need dual conversion receiver crystals. Your transmitter crystals should be OK, though.
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Old 07-20-2004, 05:17 PM   #6
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Sorry, can't help you with the crystal question, but the personal transponder will definitely work in the battery port of the receiver. For what it's worth, so will the little Reedy heatsink fans.

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Old 07-20-2004, 05:39 PM   #7
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Have you considered using a Novak XXL ?? Compatible with your radio, uses standard crystals and there always available on ebay or you might find one in the rctech classifieds. I took a look on Ebay for you and there's a few for around 40 dollars buy it now. With 2 day air or Priority mail...you could have one by the weekend. Good Luck
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Old 07-20-2004, 08:27 PM   #8
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I do have one I can use. I stole the one out of my Mini-T. It is actually a Futaba R133F (the one that says it requires "short" crystals) - Obviously I have a crystal that works with it, since my Mini-T worked.

This does bring up a couple of questions (and maybe one answer).

I talked to a guy at Futaba to try and find out what "short crystals" are. All he wanted to tell me was the stock number that I needed so I could order it - but I did sort of get out of him that "short crystals" are single conversion crystals, as opposed to dual conversion. He would not go as far as to say that all single conversion crystals would work with this Rx though. He did say that the crystals had to be Type 72-12. I only have 2 sets of crystals - the one that was in this Rx IS 72-12, but the other set I have is Type 72-7.

That brings my new question - what is the difference in 72-7 and 72-12? Anyone know?

Next question, a little simpler - how long should the antenna be for 75Mhz? I am pretty sure this antenna is not the right length, it just looks too short. It also has a cut down to the actual wire near the Rx, so I thought I should replace it - is there anything special about that wire, or is it just very small gauge wire?

Thanks everyone... Eventually I will figure all of this out. I thought it was just a matter of getting a Tx and Rx that were the same modulation and frequency - then crystals were pretty much universal...
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Old 07-21-2004, 07:15 AM   #9
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Some receiver crystals - e.g. those in Kyosho Mini-Z - are physically shorter than others, but otherwise identical. The manufacturer will tell you that no other crystals will work, but that's not entirely true. It's only a matter of space. I'm not absolutely sure that this is the case with Futaba's "short crystals", but I'm guessing.

Since you already have a Futaba R133F, compare the crystal with a regular one and see if it isn't a couple of millimeters shorter. If it is, see if you can fit the regular size crystal in the R133F. Then turn on your radio and see what happens. It may very well work.
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Old 07-23-2004, 10:01 PM   #10
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Default Follow Up:

I got a reply from Futaba Tech Support - here is a breakdown on the crystal part numbers

72-7 FM single conversion
72-10 FM dual conversion
72-12 FM short

Also, the best I can calculate, the antenna should be about 18-19 inches long for 1/8 wave 75Mhz.
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