AckMan

Hi all,

does anyone know where to get info on tuning receivers?

In paricular, i have some FP-R122JE (27MHz) receivers that i'd like to tune up. I have access to pro equipment and pretyy good RF knowledge, but never attepmted to tune one.

Also, it would be nice with some info on tunig TX as well, though it's not that urgent.

Thanks!

/Mike

Piet Le Roux

I only have experience with JR 700 receivers. You have to pickup the signal just after the discriminator. The R7** receivers are easy in this regard because of the DSC data input. The DSC enable you to test your plane with a buddy lead without switching the TX on, maybe Futaba has something similar. You can use the DSC input as a discriminator output else you have to solder a test point to the discriminator. This means that you can test and align the analog part of your receiver. The receivers I worked on were 35MHZ, so it has a coil in series with the antenna that will result in some loss. A good 35MHz receiver normally needs about 5 micro volts modulated at 3 KHz for a 12 dB sinad result (With the coil in circuit). For AM equipment you would need about 8 micro volts at 80% modulation. On the TX you just need to check the TX frequency and modulation Levels (not more than 80%).
Note that on FM equipment the modulation is done by square waves and your normal modulation meter will show about 30% less than the actual modulation.

Be very careful that you do not break the small ferrite slugs when you do aliment. If they have beeswax on them first heat them and then turn them when they are still warm. Also try to use soft aliment tools, avoid ceramic tips, they break the slugs! I had a very hard time to get circuit diagrams for JR equipment and I suppose you will too with Futaba equipment.
Good luck
Piet Le Roux

AckMan

Thanks Piet Le Roux,

for your advices, highly appreciated and most welcome. Indeed, it's hard to find any info on Futaba receivers, virtually impossible it seems. Yes, this an AM receiver, and there is a trim coil in in the antenna path, just like your 35MHz JR receiver.

Have no idea if Futaba has DCS in their receives, someone who knows more on this issue?

Thanks again and best rergards,
Mike

Dr1Driver

Unless you're a TRAINED radio technician, don't. You'll risk your plane and everyone's safety.

pretyy (sic) good RF knowledge, but never attepmted to tune one.
That doesn't work for me. A little knowledge is a dangerous thing. Send them off to be PROPERLY tuned or simply buy new ones. They're not that expensive. At least not expensive enough to be risknig a plane on.


Also, it would be nice with some info on tunig TX as well, though it's not that urgent.
I don't know about the Phillipines, but here in the US, unless you're a LICENSED radio technician, it's illegal.

Dr.1

AckMan

Thanks for your concern, but there is no reason for you to worry. I've been designing industrial electronics (including RF equipment) for more than 20 years, so i think i'm quallified enough.

FP -R122JE is a car RX.

The Philippines are basicly law-less in theese terms. In fact, it's totally corrupt (sad but true). However, much of the legal structure is inherited from US due to the fact that US helped rebuild the Philipines after WW2. Additionally, the endless stream of money that was "invested" as a result of the US bases that was here until recently have forged the system here. It's quite an interesting actually.

So my question is still open if anyone else has some advices!

Best regards,
Mike

Dr1Driver

I've been designing industrial electronics (including RF equipment) for more than 20 years, so i think i'm quallified enough.
You can always tell an engineer - you just can't tell him much.

US helped rebuild the Philipines after WW2. Additionally, the endless stream of money that was "invested" as a result of the US bases that was here until recently have forged the system here. It's quite an interesting actually.
Sounds like we made a big mistake there.

Dr.1

Piet Le Roux

It is like saying that a super bike racer should rather keep away from a BMX if he has not tried it before. I demolished my first radio at seven, repaired and aligned my thirst at 10 and I am now 46. I still make mistakes but I think I am getting the hang of it!

South Africa have no restrictions on RC repairs and servicing.

AckMan

What can i say? You nailed it

Oh yes, if you start to dig into this, you wont beleive your eyes. There is a couple of good books on the subject, one is "Waltzing with a dictator" (don't remember the author) that covers the years with Marco. It's amazing to see what happened behinf the curtains, but very sad reading, it's all about money, politics and prestige. So much people died and suffered and US gov know all about, just did not give a ****.

Btw, i know why you wrote what you did, and partially agree. The world is full of "consumer bone heads" that makes life difficult for others. But that's no reason to assume that everyone is like that.

/Mike

AckMan

We do share a common history i think. I was given so many toys when i was a kid. Few of them are still around, instead they were destroyed as part of my ambition to repair and/or understand how things worked.... Few things are destroyed like that theese days, but from time to time prototypes do show unpredictable and highly entertaining side effects that was not in the spec

Cheers!

/Mike

A.T.

Near the point where the antenna connects to the circuit board is an adjustment most receivers. It is used to peak the RF input to the exact frequency desired. Shops which do this will know where to monitor the signal with an oscilloscope.
Unfortunately, in your case the Futaba R122JE has no provision for retuning. [Of 10 tested new out of the box, only 2 had range close to that of a Hitec 2ch RX, the rest with various range tests down to only 4m - not recommended for sailplanes] As the aerials often corrode and or break when typically used on cars or boats, a failing R122JE may be revived by simply fitting a new 50cm aerial . Also open the case, remove board and brush pins and bottom of the board with a dry toothbrush to remove all built up dirt or corrosion which also impair operation of an RX.
It is possible to get quite close by monitoring the sensitivity of other RX using a servo, as set out below in previous comment ex rec.models.rc.air.
Alan
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Just connect a servo to the open receiver, turn on your transmitter with the antenna retracted and some distance away. Adjust the can until the servo jitters in one direction and then the other. Readjust to the center of the range.
(For 72 MHz) Futaba adjust their receivers for a peak at about channel 25 or 50 depending on whether crystals below or above channel 38 will be used. It usually isn't necessary to retune at all if your crystal is between the two tunings. You don't need to retune if you stay within the low
or the high band either. Retuning may be a good idea if you are moving from one end of the band to the other. But, don't get too hung up on it. If you get a good range check, don't worry about it. Jim - AMA 501383 "James D Jones" 05.05.03
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"There is a range of Rx which can be purchased in the UK as a ready built Rx or as a kit. If you buy the kit version then the instructions for *peaking* the Rx with the crystal to be used is exactly as stated above. Leave the aerial down on the Tx and keep trimming for no servo chatter while steadily increasing the distance from the Tx. Range with Tx aerial down is about 40 yards and many people have built and used these receiver kits and are very satisfied with them.
It is not exactly rocket science after all, the crystal determines the frequency. You plug in a servo after gently turning it so the arm is to one side. By trimming one of the coils the servo should centre and then be capable of being operated with one of the Tx controls.
The other coil is then adjusted for maximum range as above. Should be easy to determine as this last coil is adjacent to the aerial lead on the PCB.
Lots of people build and use these Rx, most of them will have no experience of radio equipment, they just follow the instructions supplied. I use them in fairly large gliders which I fly at quite long range. The firm that sells them has been around quite a long time now. Reg 06.05.03
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Regardless of who tunes it, be careful that you dont break the core slug if it is of this type. Try not to use a metal screwdriver or a hex wrench. ONce cracked, it looses its effect and you are down for a repair. Some cores are waxed in place to prevent movement from vibration. If it is a variable capacitor it isnt so bad but you still have to know what to look for. - Jim Breeeyar
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Much more under "Radio Systems, Accessories, Alterations and FAQ" on my web page.
Regards
Alan T.
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