FlybyPDX

My Feedback: (2)

From what I understand a dual Conversion RX has 2 crystals. is this true? I have a hitec 555 and it is dual. WHy does it only have one crystal?


How far will a single Conversion RX go? (GWS 4ch)

Rodney

That second crystal is a different form factor and not readily removable or replaceable. Yes, all dual conversion receivers must have two crystals.

FlybyPDX

My Feedback: (2)

ok. How far will a single travel??? 1000 feet?

Rodney

The signal goes on forever, just gets weaker and weaker. as to how far you can receive and convert it to intelligent information is another story. Much depends on the quality of the receiver, some are better than others. This is usually measured in dbm and (don't quote me on this) I think is usually about 3dbm for a good receiver with a proper setup. Of course this assumes a typical transmitter (1/2 watt into the final) which should give you at least a mile of useable range. Now, some of the park flyers use transmitters that put out less power and, in my opinion, receivers that are quite insensitive which often limits range to a 1000 feet or less. With the usual transmitter and receiver, you can get well over a mile of range in the air.

Mac_Man_UK

Re the 2nd Crystal inside DC receivers, these are usually a fixed frequency of 10.7 MHz ( JR DC Rxrs ), the removable crystals are usually 11.155 MHz below channel frequency. When mixed and filtered with the incoming RF signal gives a 1st IF of 11.155 MHZ which is then mixed with the fixed freq of 10.7 MHz and after filtering gives a 2nd IF of 455 KHz which most receivers use them to demodulate and process the incoming data. As this 10.7 MHz is fixed in frequency and non-removable, it can be in a much smaller package glued to the pcb.

Re how far a signal will radiate, as previously stated it will theoretically go on ad inf. Works on the Inverse Square Law, and isnt a linear reduction. Difficult to describe without using diagrams,
but the graphic here ( http://hyperphysics.phy-astr.gsu.edu...sion/isql.html ) describes it well.



[8D]

dirtybird

My Feedback: (5)

You won't get very far with a receiver with a sensitivity of 3dbm. Dbm stands for decibels referenced to one milliwatt of power. It is a standard established by the US military. Most good receivers have a sensitivity in the order of -100 dbm.
Our receivers were usually rated in microvolts of sensitivity, a figure of 1 microvolt being very good
A single conversion receiver can be just as sensitive as a dual conversion receiver. Dual conversion is used to eliminate the reception of the image frequency and has nothing to do with the sensitivity of the receiver. I have a Multiplex single conversion receiver that I use interchangeably with my other receivers.
In another thread I mentioned where we obtained reliable communication with a spacecraft orbiting the moon with as little as 2 watts of transmitter power. The receiver on the spacecraft was a single conversion unit.

JPMacG

My Feedback: (2)

Good explanations.

One comment.... dB is for decibell, one tenth of a bell. Bell is a unit named after its inventor, Alexander Graham Bell of telephone fame. It is a power ratio expressed on a logarithmic scale. As a ratio, it doesn't mean anything unless you reference it to something, like a milliwatt (dBm), watt (dBw), the carrier power (dBc), an istropic antenna (dBi), etc.

Rodney

You are correct Dirtybird, thanks for correcting my mistake. It has been quite a few years since I was involved in the measurements of RF (Mercury, Gemini and Cruise Missiles) and I have grown rusty on the exact details. Probably what I was recalling was measurements we made on the old Kraft units back in the 60's and the results were more probably 3db/microwatt. Thanks, Rodney

Ernie Misner

Here's an example of a modern, full range single conversion rx:

http://www.servocity.com/html/4-ch_hfs-04mg_fm_rx.html

Does anyone know if the hitec crystal for this single conversion receiver is the same one that is used in the dual conversion receiver?

Thanks,

Ernie

Rodney

Single conversion and dual conversion crystals are very different and not interchangeable.

Ernie Misner

Thanks Rodney.

Okay, since the above mentioned Hitec receiver is single conversion and full range, is there any reason to think of it as "inferior" to a comprable dual conversion receiver?

Ernie