The time I was listening to AM aircraft communications on a VHF Astro Saber...

[ElroyJetson]

I thought I'd post this just for the interest of it.

Many years ago when I learned to hack the CPS frequency limits, just for fun I hacked the Astro Saber CPS and dropped the VHF band limit from 134 MHz to some ridiculous low number, I think 100 MHz, just for fun.

I then programmed in the VHF-AM aviation frequencies in use in my area. Just to see what would happen.

And you know...it actually worked. Sort of. But sounded off frequency. So then I reprogrammed the radio with additional frequencies, at the minimum possible frequency shifts between them, to let me "tune" it as well as possible.

Turns out this works on the principle of "slope tuning", where there is some residual FM present on the edges of an AM carrier and this can be detected.

There is also a point at which the VCO won't lock below a certain frequency. But I was able to hear some traffic including approach and control for some major airports. I think it worked well down into around 122 MHz before going unlocked.

If you're bored, and know how to hack a given type of CPS's band limits, you might want to try this just for fun.

If you do, please report back on your results. Can you get intelligible audio quality and how low will your radio tune to before the VCO unlocks?
And of course, what kind of radio is it?

 

[alcahuete]

Some of the newer CCRs do it. I have had my Anytone 878 into portions of the airband, but of course it sounds like crap. Definitely intelligible, but sounds like crap.

 

[jruta]

It’s good to see you active. I learned so much about sabers/Astro from reading your posts when I got into radios some 20 years ago (B-labs maybe?)

 

[ElroyJetson]

Yeah, I was active at Batlabs in the before time. (Before its control was handed over to people of ...a certain character...who promptly destroyed the site as a significant knowledge resource....)

Just for fun, the Batlabs site owner, Lee, elevated me to administrator level and boy was that fun! The "self anointed kings" of the site lost their tiny little MINDS over that! It was like a firecracker in a fire ant mound. We laughed about it for months.

I later learned just about everything there is to know about the XTS platform, far more than I learned about Astro Sabers, but I'm pretty much in the dark about anything newer.

 

[jruta]

Yeah, I was active at Batlabs in the before time. (Before its control was handed over to people of ...a certain character...who promptly destroyed the site as a significant knowledge resource....)

Just for fun, the Batlabs site owner, Lee, elevated me to administrator level and boy was that fun! The "self anointed kings" of the site lost their tiny little MINDS over that! It was like a firecracker in a fire ant mound. We laughed about it for months.

I later learned just about everything there is to know about the XTS platform, far more than I learned about Astro Sabers, but I'm pretty much in the dark about anything newer.

You were definitely a wealth of knowledge on that site. The newer stuff is just more expensive haha. And I avoid that persons site (if it’s who I’m thinking- if it’s even around anymore)
This site is a much friendlier place, save for the occasional derp.

 

[prcguy]

Its much easier to receive FM on an AM receiver with slope detection and you can also transmit on FM and be heard ok on AM if you shift the carrier about 5KHz. There was a version of Saber CPS called "LAPD 10MHz" which moved the band limits 10MHz on just about any band Saber. I remember using it on my mid band Saber, which didn't do the full 66-88MHz range but it did allow me to get into the FM broadcast band.

 

[KevinC]

Its much easier to receive FM on an AM receiver with slope detection and you can also transmit on FM and be heard ok on AM if you shift the carrier about 5KHz. There was a version of Saber CPS called "LAPD 10MHz" which moved the band limits 10MHz on just about any band Saber. I remember using it on my mid band Saber, which didn't do the full 66-88MHz range but it did allow me to get into the FM broadcast band.

FM broadcast band…what an excellent place to hide.

 

[chrismol1]

FM broadcast band…what an excellent place to hide.

lol and every person with a car radio, boombox, cell phones FM equipped, baofeng can listen in or if maybe somewhat in between FM channels? I have an idea, FHSS between the FM channels if possible, I'd think that would be sneaky place to hide

 

[prcguy]

FHSS works great between FM broadcast channels. The Harris Falcon series does that and with Citadel encryption if you please. Don't ask me how I know this.

lol and every person with a car radio, boombox, cell phones FM equipped, baofeng can listen in or if maybe somewhat in between FM channels? I have an idea, FHSS between the FM channels if possible, I'd think that would be sneaky place to hide

 

[KevinC]

lol and every person with a car radio, boombox, cell phones FM equipped, baofeng can listen in or if maybe somewhat in between FM channels? I have an idea, FHSS between the FM channels if possible, I'd think that would be sneaky place to hide

A FM broadcast receiver would be too wide to decode a nice narrowband transmitter.

 

[KevinC]

A FM broadcast receiver would be too wide to decode a nice narrowband transmitter.

Beacuse honestly, how often do you search the FM broadcast band at 5 kHz steps?

 

[ElroyJetson]

Such a signal would be very faint when received by a receiver made to pick up FM stations with a peak bandwidth of 200 KHz.

 

[prcguy]

And the hopping is very fast, looks more like noise. You would never hear anything on a even a narrow band receiver.

Beacuse honestly, how often do you search the FM broadcast band at 5 kHz steps?

 

[RFI-EMI-GUY]

And the hopping is very fast, looks more like noise. You would never hear anything on a even a narrow band receiver.

I have always wanted to covert an LMR to FHSS. Find some model that will accept BCD channel inputs on VIP I/O's , program a pair of them to random channels and program a PIC to hop through a pseudo random sequence. Have a random collection channel synch them up on tone decode like those old BK radios. The radios would have to be able to switch channels during PTT.

 

[TDR-94]

FHSS works great between FM broadcast channels. The Harris Falcon series does that and with Citadel encryption if you please. Don't ask me how I know this.

That also depends on which Falcon series model of radios. The Falcon III RF-310M-HH, as I eventually came to find out, doesn't support any kind of frequency hopping or Citadel encryption.

 

[ElroyJetson]

I think that's a legacy of SINCGARS and was left behind.

 

[prcguy]

No, I'm referring to Harris Quicklook frequency hopping which can be set up from the radio front panel. You can't make use of SINCGARS hopping as there are no hopping key generating devices available to civilians, they would be illegal to own.

I think that's a legacy of SINCGARS and was left behind.

 

[TDR-94]

Yeah. Quicklook is an exportable frequency hopping waveform. No relation to SINCGARS. The hop sets for SINCGARS are treated like classified material and are usually loaded by the same "devices" that load COMSEC keys. SINCGARS, and most of the other DOD centric waveforms, are completely useless in the hands of civilians.

You can however, utilize the conventional UHF/VHF AM airband frequencies just fine with those radios.

 

[ElroyJetson]

I don't know much about SINCGARS, but I now distinctly remember that a friend of mine who dealt in a lot of radio and electronics surplus, much of it .gov surplus, had what I now know to be a hopset fill device. For all I know he still has it.

 

[prcguy]

There is an intermediate hopset fill device called the MX-18290, small with a couple of multi position switches and a push button. They are not hard to find and not restricted, unless they contain an active hopset. The MX-18290 does not generate the hopset, they are loaded with hopsets from the key generator which is the impossible to find item. I suspect your friend had an MX-18290.

The hopset key generator is larger and takes in a punched paper tape with the hopset code and the key generator and any punched tapes would be classified and restricted items. This is why we like the Harris radios with keypad programmable crypto and hopping.

I don't know much about SINCGARS, but I now distinctly remember that a friend of mine who dealt in a lot of radio and electronics surplus, much of it .gov surplus, had what I now know to be a hopset fill device. For all I know he still has it.