HT as packet radio
Imagine, if you will, a packet node with a dozen separate dual band antennas, possibly just J-pole antennas, each connected to an inexpensive dual band transceiver.
Each of the radios at the node site have transmit on one of 440.025, 440.050, etc up to 440.300.
Each of the radios receive on 2 meters at 144.31, 33, 35, 37, 41, 43, 45, 47, 49, 145.51, 53, 55.
Down in the valleys on each side of our ridge are a dozen packet stations, each with their own, dedicated purpose, always ready, point to point link up to the node site.
Every station gets the full benefit of their own dedicated link.
This would be a hundred times faster than those same stations sharing a single repeater.
There would be no Ppersistance requirements.
No delays at all.
The cost of this system would be two dozen J-poles, and two dozen really really inexpensive dual band handie talkies.
The quality for cost is most excellent.
Since the radios at the node site are all listening on a band that is empty, since the transmitters are all on a different band, there is no need for filtering or much in the way of frequency diversity.
This is much easier than any support system I could have come up with otherwise.
So... why don't we do this?
Well, let me tell you a story.
I went out and bought several of these radios and put them on packet radio.
It was a soul shattering experience.
The inexpensive dual band radios are truly terrible.
They are so noisy that you can't actually have a dozen of them in the same room on the air at a time unless the stations they are listening to are very strong.
They wouldn't perform in a commercial environment reliably, if at all.
Read on.
This is really bad.
I recommend against using the modern inexpensive HT radios for packet, especially if you are buying the equipment on purpose for that application.
You'd be much better off with 30 year old used ham radio mobile gear, with more power, more selective receiver, more predictable operation, easier UI, and less RF into your digital equipment, easier connections, easier power hookup, and nearly the same cost.
A serious consideration with modern HTs is that the designers are interesting in optimizing voice quality and battery life with no consideration for how this impacts packet radio use.
Sacrifices can easily be made which increase usability for voice, but which make packet radio work worse and be more difficult to align.
Audio level consistency:
A packet radio receiver modem wants to see an audio level that is both consistent across a packet, but also nearly the same for multiple tone frequencies on a packet.
FM voice radios don't need to behave in this way.
Indeed, voice compression, bad for packet, actually sounds great on voice.
DC signals (BIAS) on the receive audio are also OK for FM voice, especially with built in speaker equipment, but this also is of questionable value for a packet radio modem.
POP and CLICK removal:
It is easy to remove pops and clicks from the audio by replacing annoying wave forms with duplicates of preceding or following wave forms, or by shifting the time of the wave forms.
This is a well documented (and no longer patented) scheme used originally in broadcast radio transmission.
This makes the receiver sound much better, at low cost, but makes packets less reliable, and this effect is nearly undetectable without an analog equipped logic analyzer.
I have on low authority that this is done in modern 2-way FM radio-on-a-chip devices.
Battery saving by disabling the radio:
By having the control processor leave elements of the radio disabled for periods of time the radio can use less battery power while quiescent, but it would also not be awake to notice the start of a packet message.
Baofeng radios are replete with this technology.
Slow RX to TX to RX switchover times
Some of the HTs had such slow switchover that they could not keep up with the other end of the circuit.
The local TNC would transmit, and then unkey to listen for the acknowledgement, but it was already too late as the acknowledgement came while the HT's receiver wasn't yet active.
Out of Band emissions
Some Chinese brand-name radios have been known to emit energy at frequencies outside the ham band at levels beyond those permitted by the various government radio authorities (D.O.C. in Canada, F.C.C. in the USA).
Transmitter leakage through the chassis affecting in-shack equipment
They have also been known to emit radio waves at near transmission levels through the chassis which can impact the stability of DC wiring in the vicinity of the radio.
This is confusing to somebody new to integrating digital, audio and RF equipment.
Buy used commercial gear instead!
Used 2-way or ham radio equipment is particularly applicable to packet radio.
In the commercial 2-way market, the Kenwood TK762G or TK862G is a fine radio for packet.
Those are on eBay at under $50 delivered, even as I type.
