50mhz range check.

[Lakc]

I just changed over from 72mhz to 50mhz, and I am getting a rather poor ground range check from my previous procedures.

I am using a Futaba 9CAP, with a brand new Futaba xmit module and 127DF reciever. I had good range checks with 72mhz with the antenna all the way down, generally around 100 feet down my driveway and across the street, but with 50mhz and even one element extended I dont check as good.

The 50mhz module draws about 66% more current then the 72mhz, and on my scope it shows a visibly larger amplitude signal with the antenna fully extended, but at only 1-2 segments extended it shows a visibly smaller signal on the end of the antenna wire on a 72mhz 127df reciever I have for testing purposes. I am not sure if that has to do with any of the internal circuitry differences between a 72 and 50mhz modules or not, and I would rather not tear apart my new 50mhz reciever to take measurements. Incidentally, both antennas are the same length.

It makes sense that the longer wavelength would have problems with the shorter tx antenna during a range check, but I lack any baseline to compare measurements. Has anyone else changed frequency bands and had to establish another ground check procedure? Possibly try with 3 segments extended? I hope I am just being overcautious and I dont actually have a problem.

[Chippie]

[QUOTE=Lakc]I just changed over from 72mhz to 50mhz, and I am getting a rather poor ground range check from my previous procedures.

I am using a Futaba 9CAP, with a brand new Futaba xmit module and 127DF reciever. I had good range checks with 72mhz with the antenna all the way down, generally around 100 feet down my driveway and across the street, but with 50mhz and even one element extended I dont check as good.

The 50mhz module draws about 66% more current then the 72mhz, and on my scope it shows a visibly larger amplitude signal with the antenna fully extended, but at only 1-2 segments extended it shows a visibly smaller signal on the end of the antenna wire on a 72mhz 127df reciever I have for testing purposes. I am not sure if that has to do with any of the internal circuitry differences between a 72 and 50mhz modules or not, and I would rather not tear apart my new 50mhz reciever to take measurements.
QUOTE]
Let me get this straight...You have a tx designed to run at 72mhz, you have changed the frequency to 50mhz...you are testing the range of the modded tx with an existing 72mhz receiver, but you have a new 50mhz receiver that you dont wanna mess with ?

This being the case, try the range check with the 50mhz receiver and see how that fairs...I would expect similar performance prior to any changes you made....and no the receiver aerials should not be the same lenght...unless there are changes within the receiver to compensate..

just my 2 cents..

[Lakc]

Sorry, let me clarify.

Im using a stock tx module and reciever, both brand new 50mhz. I am just using the 72mhz reciever to measure voltage on the antenna wire with my oscilloscope. I am a bit reluctant to break open the new reciever to duplicate the test. I always have had good range checks with the old 72mhz tx module and recievers.

And yes, Futaba states that their receiver and tx module are tuned to use the stock antennas.

[Chippie]

.

Im using a stock tx module and reciever, both brand new 50mhz. I am just using the 72mhz reciever to measure voltage on the antenna wire with my oscilloscope.

The point you are missing is that the selectivity of the receiver is such that it is designed to amplify the signals it was designed to receive...and reject those it wasnt designed to recieve....hence the disparity in your checks...
Hope that makes sense.?

Hmmm...I just re-read everything...I may be confused...but.....you are using a 50mhz tx module in a 72mhz tx, but using a 50mhz rx to match ? Gottchya....

What you need to do then is isolate which bit isnt working properly..either the tx output is attenuated or the receiver isnt sensitive enough...maybe off-tune...alignment issues? Do you have access to another setup? That would help isolate the problem area..

[pbunn]

You may have a problem with the transmitter module. I have the same transmitter and receiver and i get great range on both 72 and 50 with considerably better range on 50 Mhz. I have noticed no extra current draw on 50 Mhz.

I also use these transmitter moduiles in vintage conversions and they work great.

[ZAGNUT]

you are using a 50mhz tx module in a 72mhz tx

the 9C isn't a "72mhz tx"...it's supposed to work equally well with whatever band of module is installed.

what worries me is the very high current draw. most 50mhz modules are pretty much the same as their 72mhz brothers aside from some component values. most 72mhz modules i've seen get hot enough as it is and would probably die pretty quickly with 2/3 more current draw.

if you don't get any straight answers from someone with first hand knowledge of futaba 50mhz modules i'd say send it back and have it replaced.



dave

[Lakc]

If anyone is interested in checking, without a TX module I have 77ma draw, I have 207ma with the 72mhz module, and 270ma with the 50mhz module. Scope shows a higher amplitude of signal coming from the antenna with the 50mhz module installed, and it looks nice and clean, but that again maybe because I only have a 100mhz scope.

[Lakc]

The point you are missing is that the selectivity of the receiver is such that it is designed to amplify the signals it was designed to receive...and reject those it wasnt designed to recieve....hence the disparity in your checks...
Hope that makes sense.?

Yes, although I am just looking at signal on the end of the antenna wire where it attaches to the board, no power in circuit, before any circuitry. I was wondering how much the remaining circuits, though unpowered, may be affecting my readings.

Hmmm...I just re-read everything...I may be confused...but.....you are using a 50mhz tx module in a 72mhz tx, but using a 50mhz rx to match ? Gottchya....

Like Zagnut said, it has interchangable transmitter modules, but you got the idea. :)



What you need to do then is isolate which bit isnt working properly..either the tx output is attenuated or the receiver isnt sensitive enough...maybe off-tune...alignment issues? Do you have access to another setup? That would help isolate the problem area..

Unfortunately, I am all out of spare 50mhz parts:) The TX and RX modules are both brand new from Tower Hobbies, not that new necessarily means good.

Everything seems fine with the antenna fully extended, I am just wondering if I should expect to see a comprable range with the antenna collapsed when 50mhz is such a longer wave.

[Tom in Cincy]

I have a 9c on 50mhz. The range with the antenna fully collapsed is about 200 feet. This is with the airplane 3 feet off the ground on a wooden airplane starting stand out in the open field on dry ground . The range is very similar to to 72mhz. Current draw on a 9c is pretty high. If you are on 50mhz please give your call letters.
Thanks, 73's
WA8ZAH
Tom

P.S. I just checked the current draw on a fully charged battery on the 9c. It is pulling 260 ma with antenna collapsed. Looks like your OK.

[GailInNM]

I just ran a quick check of my 5+ year old Futaba 50 mHz module. Using a bench supply to feed the transmitter so I didn't have to make up an adapter to insert in the battery line, I adjusted the voltage to be 10.0 volts at the transmitter. Different model transmitter than yours. Subtracting out the transmitter idle current with the module removed a measure 130 mA with the transmitter antenna extended and 160 mA with the antenna collapsed. This compares to the current you show for your 72 mHz module and much less than what you mesure for your 50 mHz module. Note that the current will vary considerably with the voltage applied to the transmitter and that your Amp meter will have some voltage drop, sometimes considerable on low current ranges, depending on the manufacture. Also note the affect of antenna extension on current.

I do not have a single channel 72 mHz module to compare with current wise, but my ground range checks seem to be comparable between 50 and 72 mHz, that is with in 25 percent of each other. Hard to call because of different receivers and installs and all the other variables.

Hope this is of some assistance,
Gail - W5MLY

[Lakc]

Thanks for all the tests and info. Ill try some more tests and pull the rx back out of the plane if I have to.
Jeff
WD8DYR <--ink not dry on license yet :)

Edit: Your correct, its KD8DYR

[dalbert02]

Thanks for all the tests and info. Ill try some more tests and pull the rx back out of the plane if I have to.
Jeff
WD8DYR <--ink not dry on license yet :)

That is strange, I could find my license on the FCC database before I got my paper copy. I too run on 50Mhz, it is great for getting away from the 72Mhz crowd. I just wish there was more support from other manufactureres like Berg, HiTech, Etc.

Look for you license on the FCC website, it shows up here before QRZ or anywhere else.

http://wireless2.fcc.gov/UlsApp/UlsSearch/searchLicense.jsp
73
-dave
KI4HVT

[Tom in Cincy]

I looked up his call also. The WD8's haven't been issued in 20 yrs. But say Jeff made a mistake and his call is actually KD8DYR now that checks out...

TP

Now aren't we a trusting group!
73's

[Lakc]

<looks at license> doh!
I was suprised, took test on Saturday, was in the database by Thursday, and paper arrived on Tuesday.
Now if I had the money for a rig, I could actually use my callsign and remember it. :)

[Miami Mike]

The call WD8DYR was issued about 30 years ago, some time in 1976. I used to have WD8AFA back then and a friend of mine had WD8DQW. I remember that we were using alternate "Bicentennial" call signs during that year, and mine was AE8AFA. I've since become a "four" after I moved from Ohio to Florida.

[Lakc]

Problem solved!

Problem was twofold, the lesser of which was trying to range check in my driveway, where the 8' wide opening for the fence gate seems to restrict 50mhz signals more then 72mhz. Putting the plane almost directly in line with the side of my brick house produced a better result, although still not as good as previously.

The major problem seemed to be the installation. After much thought I decided to add a second aileron servo, and run the extensions towards the nose of the plane. My theory was the extra counterpoise would help, and it seemed to, increasing the ground check from 70' to about 106'.

So, I would guess the lesson learned here is with tight installations and standard sized servos, longer wavelengths might need the wiring spread out a little bit more. Plane was a 4star-40.

[Nicetie]

I don't understand what you are testing, but the 72Mhz antenna is directly connected
to a 72Mhz tuned ckt that should attenuate out of band signals even when unpowered. Looking
at a 50Mhz signal with this antenna should indicate a much
lower voltage. :confused:

Ken K5MBV

[Lakc]

I don't understand what you are testing, but the 72Mhz antenna is directly connected
to a 72Mhz tuned ckt that should attenuate out of band signals even when unpowered. Looking
at a 50Mhz signal with this antenna should indicate a much
lower voltage. :confused:

Ken K5MBV

Ken,

That was exactly what I was expecting, thanks for confirming it.
Jeff