raytheon

HOW MANY ARE USING 440 MHZ ATV FOR THE VIDEO TRANSIMITTER. SEEMS ALL ARE USING TRANSMITTER IN THE GIG RANGE. WHAT ARE THE PROBLEMS WITH THE UHF STUFF ??? IF ANY ?? THANKS

mr.rc-cam

Back in the early days of ham ATV, the 434Mhz stuff was VERY popular. Mainly because the cost for microwave solutions was prohibitive at the time. This has all changed in the last three or so years and microwave based video is now very affordable.

One problem with 434 Mhz video is that the video carrier is AM (900Mhz and up all use FM). As such, AM can suffer from color fidelity issues, especially in our application where one end (Tx) is moving around. Another minor issue is that the antenna size is 5X bigger than a 2.4Ghz system.

The 434Mhz systems are often paired up with a TV and are tuned to a cable channel (to eliminate the need for a RF down-convertrr). Sadly, TV's have low sensitivity. So much higher RF power is often needed to get decent aerial LOS range. This can also be solved by using a traditional down-converter in the RF chain, at the TV tuner input, but that adds more expense.

Despite being old technology, the 434 Mhz systems tend to cost more than the other ATV bands. Very few new designs are being offered at 434 Mhz since it no longer offers a mfg cost advantage.

Frankly, for aerial video, I highly recommend a 2.4Ghz system. They are generally affordable and most are offered in the allowed ham frequencies.

raytheon

OK , I HAVE 440 ATV EQUIPMENT AND KNOW PEOPLE WHO USE THE 2.4 GIG STUFF AND " GET SNOW " WHEN THE PLANE BANKS . I HAVE BEEN INVOLVED WITH 440 ATV BEING SENT FROM A FULL SCALE PLANE AND FROM MY MEMORY THAT WAS VERY GOOD. WOULD THINK THAT IT WOULD BE AS GOOD FROM THE MODEL BUT ????????

mr.rc-cam

I think the poor experiences with microwave gear are due to installation issues (antenna related) and low quality equipment. I'm using both 50mW and 200mW 2.4Ghz systems. They have very high sensitivity PLL based Rx's. Most of the time my results are nearly blem free. The higher bandwidth of the microwave RF offers stunning quality (better than my camcorder can take advantage of).

For incredible high altitude 900Mhz and 2.4Ghz video, you should look at cyberflyer's site: http://www.cyber-flyer.com/2003/flight_log.html

Also, Yb2normal's clever Homer video also shows what a decent 2.4Ghz system can do: http://www.rcuniverse.com/forum/m_13...tm.htm#1358216

mithrandir

My Feedback: (2)

Well.. I kinda lack all the mojo to get this milli-watt stuff to work. I have opted for the 426.25 mhz ATV setup and 1.5 watts of power (Yes I have FCC license)... I am still in early stages, I can not say it is better yet, but I dicked around with the 2.4ghz stuff, and quickly realized that much of the stuff out there has been modified, thus illegal (Yeah, I know.. so what... what will the fcc do to people running 150 milli-watt on 2.4?!?!?) And it suffered from poor range, and sensitive to antenna orientation. My dream setup is 3000 feet of solid range with plane in any attitude.. so far no cross country flights are planned. My limited understanding is that higher freq = less range. This seemed important to me. I got most my stuff from http://www.hamtv.com and http://www.aesham.com/ I will keep yuh'all posted as far as my success/failure!!! LOL So far I am about $400.00 into it, and I have everything 'cept batteries. I also had a 12 volt DC tv/vcr combo.

rc bugman

My Feedback: (30)

mithrandir

I use your exact HamTV setup with a higher quality receive antenna in my university research project and I get excellent video at distances exceeding a mile. My receive antenna is a 102" CB whip tuned to resonance with an antenna tuner (MFJ 2m & 70cm). Since my receive trailer also has communications gear transmitting, I use a 420-440 band pass filter to eliminate the other frequencies for transmitting antennas very close by (a matter of a few ft). I do use a downconverter before the TV but I don't think it is really necessary with the receiving antenna setup.

For the airplane, I actually use 2-tuned dipoles with one oriented vertically(along the vert stab) and the second one oriented horz (along the leading edge of the horz stab). To tune this type of turnstile antenna, the length of one of the coax feeds needs to be 1/4 wavelength shorter. Both coax ends are fastened to a T-connector which is connected to the TX antenna connector.

This antenna setup fills in the antenna nulls as the plane rolls from vertical in a turn but the effective radiation from each antenna is only 3/4 watt.

This is a very effective system and I think I could get a longer distance if need be.

Another issue you need to be aware of is the tolerance of your RC receiver to an onboard tx with 1.5 watt power. Many brands of receivers are not tolerate of these circumstances. I have found with a lot of testing that the FMA Quantum or newer models of the FMA rxs are the most forgiving of onboard txs and have the best rejection of out-of-band high-power RF. You would be well advised to stay away from PCM Rxs which merely mask interference problems. I have lost a couple of research planes during the learning curve.

I hope this helps

Elson K2BUG

mithrandir

My Feedback: (2)

Hey Bugman... well.. I am more of a Structures/Aero guy! I have been getting all of my info from here.. http://www.hamtv.com/pdf.files/R-C.pdf. I intend to shield my Rx with the installed band pass filter. You have any experiance with this? I am intending to use FUTABA PCM ham-band Rx as well.. I have 72 mhz if that is better. I will be doing initial range tests on the ground to get warm fuzzies, and my first flights will be with a tired $89.00 ARF trainer and an old motor. I will setup "FAIL-SAFE" to shut off Vid-Tx if should FS be invoked. But this is all new stuff to me too... I have flown models since 1972, but this new stuff... and electronics is all voodoo and magic!!! Any feel as to how sensitive to damage this is without tuning antenna? I can Calc-Out the exact element length for the Tx antenna, but I have no meter to check the SWR's.

rc bugman

My Feedback: (30)

mithrandir

Based on my experience with ATV and RC planes which is a bit more than the hobbyist, I would just spend the $60 on a FMA rx in either 72 or 50 mhz. Japanese receivers seem sensitive to RX front end overload and if you are not careful, antenna filters which you build and add on can reduce the sensitivity of your rx to the frequency you fly on.

Typically, planes with tv txs with range check ok, but you will run into control problems once the plane is more than 300 yards from the RC Tx. PCM receivers just mask the problem until it is too late.


Elson

hobbyboy

My Feedback: (1)

This is another reason that 2.4 works so great. I have tried up to 3 watts on 2.4 12" from my Futaba receiver and flown a GPS confirmed 1/2 mile with no control issues. This was out of sight using the downlink as the control medium on a helicopter with no concern for shielding on the receiver. I do like the fact that 440 is less directional, but don't like the other issues with it. I am curious to see how it works out for you. Bob