I have, generally the only way this works is when the radios (and then some radios only, not all) are very close together or the signals are very strong, then you get IF image issues going on, and can hear the other station. But often reduced in strength, sometimes by 30 dB or more.
Well I would imagine it depends on the antenna on your radio.... That much lower freq would cause your match to go sky high and yes your output would be reduced most likely.....
You left out my edit (the next paragraph) that went into a little more detail:
(edit for clarity) What you are describing is possible with poorly designed radios, as they may suffer from poor image rejection. So it is very dependent on the specific radio. Very early or very inexpensive radios are more likely to show this. A well designed radio with some thought in RF bandpass or tracking on the front end will not do this or if it does will show great attenuation of the signal.
As for antenna and antenna match, older radios like what are being discussed tend to be more robust when it comes to SWR mismatch than anything made in the last 40 years. Many, probably most, of these older radios have no automatic fold back if the SWR is too high. So high SWR or not, they try to make as much power as they are adjusted for on that particular frequency. Of course there is some reduction in power caused by multiple issues. The reflected power (or return loss), obviously, but you have to get up to 6:1 SWR before half the power is returned. Antenna inefficiencies, how little of the power put to the antenna actually gets radiated into free space, of course will be a factor.
But the big factor I was talking about is the design of the receiver front end, the bandpass filter and how it works.
A radio tuned to channel 1, with a set of TX and RX crystals as described and a 455 kHz IF, would have a TX and RX frequency of 26.965 MHz. The TX crystal would be on 26.965 MHz, but the RX crystal would be on 26.51 MHz. The RX crystal is cut to 455 kHz below the desired receive freq, and the IF is added to the RX crystal controlled oscillator.
The other issue, and the thing that the technique Reverend Bow was talking about leveraging, is the fact that the receiver
also has the potential to receive a second frequency, which is the RX crystal freq
minus the IF, instead of plus the IF as intended. This would tune the receiver to a second freq at the same time as the first, in this case the 26.51 MHz crystal freq minus the 455 kHz IF, making 26.055 MHz.
Receiving a second frequency when you mean to receive only one can be a problem. So the designers put in a bandpass filter (BPF), sometimes only a high pass filter (HPF). I will only talk about a BPF, but an HPF would have the same issues. The exact design and adjustment of this filter will determine the fc (cutoff frequency, or the "edge" of the filter, below which it will try to block signals from being received) and how steep the filter skirts are (how closely, in frequency, they knock down signals outside the desired frequency range).
Since we are talking about 23 channel CBs here (you almost never find a 40 channel CB with RX and TX crystals for a given freq, they used other techniques even when crystal controlled) it was pretty simple to determine what the fc of the BPF should be for a good design. Channel 23 is 27.255 MHz. Minus the 455 kHz IF leaves 26.8 MHz, this would be the RX crystal freq. And so the IF image would be on 26.8 MHz minus 455 kHz, or 26.345 MHz. The basic scheme of the radio would be trying to receive both 26.345 and 27.255 MHz.
If the designer wanted to make sure the radio would only receive the desired frequency, and not the undesired IF image, he would put in a BPF that had an fc above the highest image freq (26.345 MHz) and below the lowest intended freq (26.965, channel 1). Steep skirted filters are more expensive to make then shallow skirted filters, so to save cost you push the fc up to as close to channel 1 as you can, often around 26.8 or so MHz.
This means that frequencies below the fc of the filter, for example the 26.8 MHz number I used, will be attenuated, the filter blocks them.
Receivers that have a well designed BPF will not do what Reverend Bow was talking about, you can't just flip the crystals around and be using a lower frequency, out of the normal CB band. But receivers that do not have a well designed bandpass filter, or have an fc below 26.5 MHz, or if you go into the radio and make a minor tweak to the BPF, will do what he has described.
Of course then you will be receiving two frequencies, both the + and - IF. For channel 1, if you flipped the RX and TX crystals, you would be transmitting on 26.51 MHz, and the radio oscillator and IF system would be trying to receive both 26.51 and 27.42 MHz (LO-IF and LO+IF) , at the same time. With a properly designed BPF the 26.51 MHz signal would be greatly attenuated. But if the fc of the BPF is below 26.51 MHz, then it will work fine.
If the designer does his job this flipping crystals technique will not work, but if he did not, or was cutting cost, it may work.
This is one of the reasons freebanding or outbanding on the upper ferqs (above channel 23 and later 40) was more popular than doing so on the lower freqs, there were more radios that would do it across wider ranges with a simple crystal swap. On the receiver side there was little or no reason to actually use a BPF, an HPF was really all that was needed. And an HPF is cheaper to build than a BPF. So the receivers tended to work well for a long ways above the legal channels. The transmitters did require a low pass filter (LPF) so they would not interfere with TV stations on the 2nd harmonic. But again, it was cheaper to build an LPF than a BPF, so a typical CB radio would contain, in the RF path, an HPF with an fc someplace below channel 1, and an LPF with an fc around 30 MHz and with not great skirts. This was a much lower cost option than building a single BPF to do both jobs, and still did things well.
T!