I cannot tell if your Tx is "on the way out", but I can give a little insight into the apparent "DEAD" areas around your field. I fly in Brisbane and at our field we used to have a couple of dead spots or places where interference was suspected. A few planes were lost in those areas.
As our club was commenced at the beginning of this month it has been undergoing a few reforms including actually having a runway and a pilots box. The pilots box is now in a different location to where it was and so far no one has suffered any suspicious signal losses.
Now bad to my tech roots, Apart from equipment malfunction, and normal distance related loss, there are only a few possible causes for real signal loss.
First to consider is what is called antenna polarisation loss. If your transmit antenna is vertical and your receiver antenna is horizontal there is an additional loss factor above that caused by distance and the Receive signal hand be around one hundredth of what it would be based on distance losses alone. The loss has always been a possibility but the older frequencies had significantly more reflections from the environment and these reflections often carried a polarisation change with them and so the signal on the reflected signal could be stronger than the direct signal and actually maintain radio connection or control. 2.4GHz reflects less well and is more line of sight. This is why most quality RC equipment for model aircraft have dual antennas for antenna diversity and the antennas are normally suggested that thye be fitted an right angles to each other. Sometimes antenna location of one of the antennas can be compromised by the other wires and metal items near the antenna and so a simple antenna relocation could remove all issues. Another possible issue can be one of the antennas being damaged or somehow compromised.
The second cause of possible signal loss to be considered is what is effectively the signal being interfered with by its own transmitters reflected signals being mixed with the direct signal but in equal level and opposite phase. For a simple method of description a positive signal is mixed with a negative signal of equal strength or level. The resultant is ZERO signal! Whilst an exact cancellation of signal is quite rare the signal can be lowered in level and in areas where there might be strong possible on channel interference the interfering signal can swamp the now weak signal and cause signal loss. This sort of problem can occur over or around metal reflective objects at the boundaries of the field like Iron roofed buildings, Wire fences, water tanks, powerlines, and even cars parked around the field. Because such an effect depends on chosen operating frequency as well as the exact position of the transmitter and receiver to both each other and the reflective objects there is a almost soul destroying infrequency about such a cause of signal loss but it does happen and can down anyone's aircraft regardless of their radio system.
Next issue to consider is something called "Blocking". Blocking is quite rare fortunately! It is when a signal is transmitted near the receiver which is off channel, (often even out of radio band), that is so strong it is received by the Rx components themselves, (in the extreme). The blocking signal actually alters the internal operation of the Rx components and the Rx looses its range or even ceases to function altogether. Extremely difficult to identify and harder to eradicate. So areas of high power signal from other sources should be avoided. Things of concern are transmission lines, transformers, radio towers, Radar installations, (including marine radars found in marinas), and finally a rather unique source of a blocking and that is where some blocking occurs but you Rx can still process your transmission BUT then some other unknowing operator on the other end of the field turns his transmitter on and with you plane far closer to his transmitter than yours his signal adds to the effect of the blocking signal and suddenly you lose all communication.
This is another reason to have operating transmitters in close proximatey to each other. No need for quarantine but have the pilot box/enclosure/area nearby to the pits is all that is recommended.
The final issue worth considering is aggressive WLAN controllers and similar that monitor for "Unfriendly signals". Such systems can identify some 2.4GHz transmissions as a possible DOS attack and then beginning transmitting in various methods in the entire band to disassociate the suspected intruder.
Recommendations!
Note "Dead areas" linked to exactly where you are. Some dead spots are caused by where the transmitter is in relation to reflective objects. Our new pilot box is much further away from all metal structures than ever before and so far the old dead spots have been silent or absent.
Renew your plane's antenna alignments and/or positions!
Fly high over suspected interference areas because the higher you fly the less interference you will suffer because almost every source of possible interference is due to ground situated or located structures and by flying high you increase the distance from them, besides you will have more time to effect a SAVE.
Keep a flight log for each Rx and note when you have an issue. Over time if an issue is plane specific you are left with either a possibly faulty Rx or a faulty installation. Build a "MULE" or assign an old and otherwise retired plane to be the MULE. A mule is in my terminology something of little or no value that you can use as a test bed for testing suspect items. A good mule is light, doesn't glide very far, normally a pusher design, extremely low or no value and something so horrible that if it does a fly away you just Smile, shrug your shoulders and select your next plane to fly. Use the mule to test out the suspect Rx or other components and the suspect interfering areas, including lower than usual overflights, (If there are no people or property to be harmed or damaged). I use a KFM4 flying wing mule it has been quite informative!
Never allow anyone to stand between you and the plane you are flying!
Just a little insight for you to ponder!
What works for me!
Have fun!
