Aussie 477 UHF CB Antenna repurposed for 2m/70cm?

[NudeLobster]

Hey guys,

I've been studying and learning a lot in preps for my ham license test and hardware purchases. I've decided to run an Icom 2730a dual band. I was going to run a Comet SS680SBNMO dual band antenna with a spring due to Comets being ground independant so I can mount it on a bullbar. I'm in Australia on a trip and pretty much 75% of all trucks or SUVs are running GME brand Radome antennas. They are very durable antennas and some questioning has lead me to find that the steel antenna whips fatigue and break commonly here on corrugations and offroad use. The more I learned, the more I started thinking....

https://www.gme.net.au/media/2689390/landantennarange_b_web.pdf

They are obviously sold, tuned, and used for Australia's 477 UHF CB band which isn't far off the 70cm band. GME has a 1040mm antenna, AE4702, that would be 1.95λ for 70cm frequency 446Mhz and 5/8λ for 2m frequency 146Mhz. That would be a great 2m match all around and good distance/directivity match for 70cm, correct? These calculations are assuming a 0.79 velocity factor for RG-58 50Ω coax, according to http://wxtofly.net/wavecalc.htm

They also have a 580mm whip that interchanges at the spring easily via SO-239 connection for less distance but also less directivity (from my understanding, right?) for rugged, steep mountain passes. This whip doesn't nearly match up on wavelengths but is fairly close to 1λ at 446Mhz and almost exactly 3/8λ at 146Mhz (I realize 3/8 isn't a common fraction/phase for antennas).

Even so, I don't see why they couldn't be cut down a smidge to tune SWR if needed, though It doesn't seem like I would need to, from this math?

Does my math/theory check out? I have found literally no information on the internet about using 477 UHF CB antennas for 2m/70cm dual bands. Maybe I'm not searching the right keywords. I've reached out to GME a few days ago without a response yet, though they may be backlogged from the super long holiday they take here in AUS for Easter!

I much prefer the durability these radome-encased antennas seem to have over standard steel-wire antennas for 4x4 use and I haven't found any US market antennas that are similar. I wouldn't worry nearly as much taking a tree-limb whack or the like, especially being right out front on the bullbar.

Thanks in advance,
Justin

 

[Paddler Ed]

Have an explore of RFI as well; they have a good range and are a bit more specialised than GME.

http://www.rfiwireless.com.au/mobile-products/uhf-mobile/uhf-ground-independant.html

Hope that helps a bit,

Ed

 

[Skeptic]

There probably isn't going to be a whole lot on the internet about using Australian 477 MHz CB band as a 2m/70cm dual band, since obviously, we don't use that band here and is perhaps used sparsely elsewhere as well. Not sure what they cost, but might be worth seeing if one loads up and you get some decent SWR and performance from it.

 

[PhulesAU]

Probably be ok for a mono bander, poor performance as a dual.

 

[NudeLobster]

There probably isn't going to be a whole lot on the internet about using Australian 477 MHz CB band as a 2m/70cm dual band, since obviously, we don't use that band here and is perhaps used sparsely elsewhere as well. Not sure what they cost, but might be worth seeing if one loads up and you get some decent SWR and performance from it.

Yeah I may be on that path soon enough... Was hoping to have some level of confidence before dropping $200USD and shipping from AUS but it may have to do. It's funny you say that, but you're completely right. The ameteur bands are the same in Australia (I know 70cm, I'm fairly certain 2m as well) but why would anyone downunder go through the pains of a licence when UHF CB is free!?

 

[Skeptic]

The ameteur bands are the same in Australia (I know 70cm, I'm fairly certain 2m as well) but why would anyone downunder go through the pains of a licence when UHF CB is free!?

Your're only thinking of licensing as a means to communicate with other 4 wheels in this context. Amateurs that are in the hobby aren't necessarily interested in that type of communication, but also in broader interests related to global HF communications, satellite, repeater use, moonbounce, emergency communications, etc. They enjoy the use of APRS, digital modes, and other features. I can legally run 1,500 watts on most amateur bands, and 2M mobile radios typically run 50 watts. Compare that to the few watts that a CB service permits, and you can get a picture of how broad and useful amateur radio is compared to CB, whether it's 477 or 27 MHz.

UHF CB has it's limits. No repeater capability, no long-distance communication capability, and not even occasional propagation opportunities that the 27-MHz US CB band experiences when conditions are good. Trail riders can get by speaking with others in their group nicely just using CB, and if that is the limit of their interest, there is no need to pursue amateur licensing. If you are truly overlanding (longer distance travel, transiting wilderness areas, etc.) then amateur radio allows you to contact others beyond the limits of CB. I haven't been there yet, but I understand that Australia has a lot of wilderness areas.

 

[sonoronos]

never mind.

 

[DaveInDenver]

When you read their marketing data it seems pretty straight forward stuff, helical wound or base loaded on lower bands and stacked array whip with phasing coils for high gain upper bands. My guess is some of them might be tunable but the ones the PO is after, the high gain ones enclosed in a radome, probably won't be intended to be field tuned.

It's kind of too bad because I like their approach to mix-and-match. They have various mounts, bases and whips that let you build an antenna that meets your needs. I wish GME would bring that approach here because it seems there's a lack of antennas intended for hard duty. The closest we get are commercial monobanders. It would indeed be nice to have those rigid whips with shock springs as an option.