The length of the string?
Might as well be. Line of sight was a thing.
The astronaut on the left is the LMP. The one on the right is the CDR. The diagram doesn't explain the suit relay correctly.
As anyone knows who uses analog AM VHF voice comms routinely, you can't both transmit on the same frequency at the same time. The Apollo radio engineers solved the problem of two astronauts transmitting at the same time by daisy-chaining the LMP to the CDR. The LMP transmits voice and telemetry over FM Channel C to the CDR. The CDR's radio combines that with his own voice and telemetry and sends that to the LM over AM Channel B. The LM then relays the combined signal to Earth via the Unified S-band link.
When the LM receives voice from Houston, it relays it out to the astronauts on AM Channel A which they both receive directly. The diagram doesn't show this.
So how does the LMP hear the CDR? Listening to Channel B (CDR-to-LM) is problematic because while the telemetry was in a subcarrier on AM Channel B, you could still hear it. That would complicate the LMP's suit radio because it would need to filter out the subcarrier.
Did Larry Baysinger hear it? Yes, he did. He was listening on Channel B. Baysinger's recordings contain the telemetry subcarrier chirping away up in the higher frequencies. (ETA: He heard them but did not record them.) Amateurs listening into the telemetry from other missions could actually hear the feed change as the astronauts did strenuous activities that were registered in their suit biometrics.
The LMP hears the CDR's voice on Channel A, but as retransmitted by the LM (or the LRV in J-type missions). The LM's radio is allowed to be complicated, therefore it can filter out the telemetry subcarrier for the LMP's benefit. The diagram should have an arrow from the LM to the LMP representing AM Channel A, not a bidirectional arrow between the CDR and LMP for voice.
So to summarize the normal mode, the LMP transmits
only on Channel C and receives
only on Channel A. The CDR receives on Channels A and C, but transmits
only on Channel B. The LM or LRV transmits VHF
only on Channel A and receives VHF
only on Channel B. That's how the frequencies were deconflicted to avoid interference and heterodynes.
There was a simplex mode available in the case of local LM/LRV relay failure. The astronauts could switch to use Channel B exclusively. But they had to switch to push-to-talk (PTT) and obey standard VHF single-frequency protocol. They were experienced pilots, so this is second-nature. Even in a failed local relay condition, it was conceivable that the LM's Channel B to USB connection was still working, so what they both said would be heard in Houston. But in this mode they can't hear Houston over Channel A. Therefore simplex mode was divided in a Mode A and Mode B in which the CDR could hear Houston over Channel A and also the LMP over Channel B, but the LMP could hear only the CDR on Channel B (not Channel A).
Failing that, there's a cable you can plug into the RCU and talk directly between the suits.
Failing
that (and this was largely untested), you can raise all the visors and physically touch the "fishbowl" helmets and yell. It was believed there could be enough acoustic coupling to allow this.
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