@Pearson 39-II
Nice write up, but a word of caution. Perhaps the current radios are built with more durable parts, in my training we were cautioned “Never Key a Mike with out an antenna attached to the radio”.
The issue is there is no where for the transmit power to go and it could burn up the transmitter final stage. Note that the DSC Emergency transmission is designed to operate in “High Power Mode”, 25 W of transmission power.
Granted my training is with older equipment, and the new radios my have circuit protection if a transmit signal would damage the radio.
I would be cautious in attempting to follow the test plan with out first checking the manufacturers instructions regarding transmitting without an antenna.
@jjssailem Your comments re: the risk of damaging the antenna-less VHF transmitter circuits are well taken and a valid concern. In fact the owner's manuals for both my modern Std Horizon (Yaesu) GX2200 and my fairly new Lowrance Link-2 handheld do advise not even keying the microphone PTT transmit button with no antenna connected. [Curiously my old Std Horizon GS1246S Eclipse VHF 's manual never mentions this].
Online research, however, mostly confirmed my own experiences. Lots of operators in the Ham, CB, SSB, and VHF communities reported they and many others they know had occasionally tried, usually accidentally, to transmit with no antenna and no dummy antenna load connected and yet went on to find no damage had occurred. Typical accidents were after they had forgotten to reconnect their antennas after disconnecting due to storm lightning. Others involved their kids. But, yes, there were also incidents where damage did occur, though I found no details of those incidents.
It was in the Wiki article on Standing Wave Ratio and antenna Dummy Loads I found “If a transmitter is tested without a load attached to its output terminals such as an antenna or a dummy load, the power will be reflected back into the transmitter, often overheating and damaging it. “ with the key word, to me, being “overheating”.
Other comments included: "Well, modern radios with their fold-back on high swr... helps protect the finals. "
"Usually, the transmitter will be designed so that the power device is sufficiently within its ratings that it won't fail into
any load, as blowing up into no load is not very nice behaviour. But sometimes, especially for low cost and high power amplifiers... it won't be, and needs that load to prevent reflections."
"But even when a disconnected antenna causes high dissipation in the final, that won't cause damage until it continues long enough for the temperature to rise. With a small transistor that can happen pretty quickly, but in most cases it is the excessive dissipation over an extended time that causes problems. This doesn't mean that it is good practice, of course, but generally brief lapses of attention such as that don't cause permanent damage as long as they don't go on for too long."
So I went ahead and tested, with no antennas, and some with my emergency VHF roll-up and telescoping antennas, and in one case with a paperclip inserted into the center conductor of the old radio’s SO-239 antenna connector just to be able to receive the WX channels! In all cases I transmitted only for a second or less, clicking the PTT button just to verify reception in the target radio, or repeatedly allowed the 0.5 second DSC distress transmission on channel 70 with many minutes between any of those. And none of my 3 radios has been damaged.
Still, since @jssailem’s cautionary comment I contacted the Techs at Yaesu to get professional information. I just got a reply today:
Question 1. Are the radio's RF transmit circuits protected against damage in the event the radio is PTT keyed with the antenna connection open-circuited as in a dismasting, antenna loss, or even accidental disconnection from the SO-239 connector on the rear panel?
Answer: “1: There is protection there, but it is not designed for constant use, it will protect it from the odd quick transmission here and there but if you continue to transmit without an antenna you could damage the radio.”
Question 2. Is it correct that a risk of damage exists if the radio is PTT keyed with no antenna connected due to RF power being reflected back into the transmitter, causing overheating? If that is the failure mode would the very brief transmission of a DSC Distress Call by the radio likely damage the radio's transmit circuits? That is, if one keys the radio for one second the risk of circuit overheating is less than if keying it for 30 or 60 seconds?
Answer: “2: Again, a brief transmission should not cause any damage but same thing long or repetitive burst will damage the radio.”
Granted, the questions were specific to my GX2200 and I am no expert in the rather weird engineering of RF electronics. However, my guess is radios modern enough to be DSC capable have also benefited from the modern availability of higher-power components, development of SWR measuring/tuning/protecting software, and the wisdom of radio designers to use these to provide more robust products.
I’m no advocate – just reporting what I’ve learned and tested and my satisfying results. I have added a cautionary note regarding this issue to my write-up and have replaced my original post attachment with that Rev2 procedure and will attach it also this post.