8UAP power upgrade wanted

[pmanu]

Hi there, Im not sure where to ask this and hope im in the correct place

I have a 8UAP TX and (40Mhz NZ ) wish to use 2.4 Ghz video tx also,

So would like to know if there are any RF power upgrades i can do to the RF stage, its always been lower in power than older radios ive had, 6VA and even the Attack 6 has a large Rf transistor about 800mw compared to the 200mw or so of the 8UAP

don't want to update TX just upgrade RF stage, ive fitted a 3 cell lipo to boost volts a little.

Cheers
Brett

[Bruce Abbott]

Just because a particular RF amp has a larger transistor, does not mean that it has higher power output. The 8UAP takes the FP-TP-FM rf module. Older modules used a 2SC2314 which is rated at 750mW, whereas the new smd version uses a 2SC4272 which is rated at 1.3W. You can get a rough idea of how much power it is actually using by measuring battery current with and without the crystal installed (or with and without the module inserted). If current is much less that expected then your module may be faulty (see this thread (http://www.rcgroups.com/forums/showthread.php?t=424182) for an example).

According to FCC records the T6VA's rf output power is 378mW, and the FM-TP-FM is 500mW. That's on 72MHz of course, it may be different on other bands. I used a field strength meter to compare my 40MHz 9CAP (with FP-TP-FM module) to my Hitec Flash5x, and the results were practically identical*. Note that EIRP (Equivalent Isotropically Radiated Power) will always be less, due to losses in the aerial and ground. In New Zealand the maximum permitted EIRP is 100mW.

*It is difficult to get meaningful results when just holding onto the transmitter can more than double its effective power output!

[pmanu]

Thanks for the reply Bruce,So hard to find that EIRP info on the NZ govt site,also silly to see that 72Mhz to be used with caution as shared by hearing impaired,another govt mix up,

I measured with module in @ 230ma and then crystal removed @ 6ma
battery @ 11 volts

If thats just above one quarter of the collector current (4.43) could i divide the 1.3 watts by 4.43 and get about 293 mW, would that be about right ?

my radio is about 8-10 years old and has the 2sc4272 smd chip, no heat sink, and does get hot after long flights

Cheers
Brett

[Bruce Abbott]

The module is consuming 2.46 Watts. However not all of this is available for output - some of the power must be going to the oscillator and multiplier stages. I will take a guess and say that 750mW is used there, leaving 1.7W for the output stage. The rf output transistor is capable of 60% efficiency, but in practice there will be mismatch and losses in other components, so let's say the total efficiency is 30% which equates to 510mW rf output power.

If the DC input power is 1.7W and the transistor is 60% efficient, then it will have to dissipate about 700mW. This will definitely make it get hot, but don't worry because this is only just over half its rating (a common 'rule-of-thumb' is to limit dissipation to half the transistor's rating), and its efficiency increases at higher temperatures!

So hard to find that EIRP info on the NZ govt siteThe laws have been changed and added to a lot so it can be hard to figure out. AFAIK the relevant document is "NZGazette39Apr071.pdf". Note that it appears that 1W is now permitted on some frequencies (ie. 27MHz and the lower half of the 40MHz band) whereas previously they were all restricted to 100mW. This anomaly will probably be corrected sooner or later...

also silly to see that 72Mhz to be used with caution as shared by hearing impaired,another govt mix up, Perhaps, but we don't know what other equipment is out there. Allocation of the radio frequency spectrum is very complex and I wouldn't want to be the person in charge of it!

Just one other thing I think you should consider - if you modify your transmitter and then some 'incident' occurs (even if not related to your mod) it might be very bad mojo from a legal standpoint :(.

[pmanu]

Thanks Bruce,

I did quick small test with Tadango FSM and got 20ma more from tip of the aerial
from my attack 4 with the 2sc2314, and it always had better range,tuned my 8uap with it and was bang on from start,

http://www.rcgroups.com/forums/attachment.php?attachmentid=616281

Vintage1 the transistor in my 8UAP is a 2sc4272 as bruce pointed out, tiny SMD 4.5x2.5 mm

it looks like it has 2 x 5.6 ohm in parallel = 2.8 ohms current limiting on the emitter- radio draws about 230ma


where as the 2sc2314 in my attack4 has 2 x 2.2 in parallel = 1.1 on the emitter- radio draws about 350 ma (DMM playing up with rf signal)

have also notice that other modules on this site use the 2sc2314 on the other side of the board where my red arrows are in picture and not the SMD that i have in the green picture with red arrow,

Bruce i rang Radio Spectrum Management today and there are a couple of ways to transmit at the 1 watt

would like to try the 2sc2314 equivalent, something that if damaged is easy replace,

any more ideas would be great
thanks
Brett

[vintage1]

Well it looks like you cam remove the SMD transistor and sub a bigger one and change the 'ballast' resistors then..