Changing a 72 receiver crystal to a 75?

Unless you have one peculiar receiver that 3MHz jump means you'll need to re tune the front end to match the new crystal. A receiver may work with the new crystal, but I'd expect a severely reduced range.

Experience trumps theory, though, so if someone has been able to give it a try and do controlled tests before and after I'd like to hear about it.

From:

Works fine with Futaba receivers 02/05/2007 Reviewer: Larry Gitchell from Northlake, IL USA I have tried this radio with 2 different types of Futaba receiver. Works with both just by plugging the Vex crystal into the receiver. Unfortunately, the transmitter crystal has a non-typical spacing on the pins, so you can't change channels on the transmitter so easily.

and:

A very good 75 mhz transmitter 01/28/2007 Reviewer: A viewer from BROOKLYN, NY US It's very hard to find a transmitter in 75 mhz, with 6 channels with mixing and at this price. I tested with my all 3 types of 75 mhz synthesized receiver (no crystal needed) all work with the transmitter. But the channel 1 to 4 are in reverse order is a easy fix, 5 and 6 ok. the receiver come with the kit was a loss.

Interesting.

Would have been better had he described the specific receivers.

If you were to pick one to try, which one?

BoyntonStu

The one that comes with a promise from the shop owner that he'll take it back if it fails a range check. Just about anything will work this way if you're standing over it with the transmitter, with the antenna fully extended and in a radio-quiet area. It's at long range, or when there's interference close by, or both, that it'll be a real issue.

Thanks,

Good answer.

My intention is to borrow a few receivers from friends and try them out at long range.

BoyntonStu

You may need to tweak the input coil for best range. Its usually the only one ON the set these days..the one near the antenna anyway.

Its dead easy to do..if you have a non metallic tool. Leave the transmitter on the ground and walk away with the model till the servos start to buzz and jitter, then tune the set for the least buzz and jitter. Job done.

Thanks for the tuning tip.

I think that I will be in radio control shortly.

As an aside, part of my hobby is to do it a little differently and as inexpensively as possible.

should do well for my video barge project.

I can use the same 12 Volt supply for the TX, 1.2 Ghz video RX, and DVD player display.

BoyntonStu

| Are there any crystal controlled receivers designed to take any | crystal between 72 Mhz and 75 Mhz?

Why are you worried about 72 MHz at all? | I have a VEX Robotic 6 channel transmitter on channel 89 and I want to | receive the PWM signals on a non-VEX receiver.

You should be able to use car RXs. I don't know if the VEX TX is positive or negative shift, however. Do the shifts for car RXs match the shifts for plane RXs? Futaba, Hitec = negative, JR, Airtronics = positive?

Cars use a lot more AM gear, so you'll probably need to make sure you get a FM RX. At least I assume the VEX TX is FM.

In any event, if you really do want a RX that can do 72 MHz and 75 MHz, the seven channel Sombra labs SHadow 3 fits the bill -- and I suspect it's the only thing available that does.

it doesn't take crystals at all, but can use any of the R/C channels in the 72 MHz or 75 MHz bands. It also can deal with both positive and negative shift.

Personally, I've got two of them and I'm unimpressed with them -- they seem to get into trouble very easily and stop responding to what I'm telling them, in situations where other RXs work fine. But for land use (where you don't go too far away) they might be great -- but there are other synthesized (no crystal) RXs for car use available too.

I'm a bit fed up with this guy.

He got a perfectly reasonble set of answers here, and has asked the same question on RCgroups as well.

QTY:Frequency/Band Changes: Receiver (only) frequency change: $20.00 (Within the same band) Receiver (only) band change (except R127DF/DP and R138DP receivers): $20.00 (72 to 75 mhz OR 75 to 72 mhz only) Transmitter (only) frequency change: $20.00 (Within the same band) Transmitter (only) band change: $20.00 (72 to 75 mhz OR 75 to 72 mhz only) Non-PCM Transmitter mode change: $20.00 PCM Transmitter mode change: $30.00 Transmitter module (only) frequency change: $20.00 (Within the same band) or you may wish to simply purchase a new module from your hobby dealer

What does Hobby Services do to a 72 Mhz Futaba Receiver in order for it to work on 75Mhz?

probably change a couple of capacitors and tweak a coil. Id say just tweak a coil actually - 3MHz should be within tuning range.