Mobile Antenna

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mcradio72

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Looking for something different than what I currently have. I have a 17 IN 25-1300 MHZ Scan Force antenna I am looking to replace for a different look preferably something that looks like the Larsen Mirage Antenna or something similar but would cover the same sort of freq range that I currently can with the Scan Force antenna.

Any Ideas?

https://www.scannermaster.com/154_156_Larsen_Mobile_Antenna_p/20-541620.htm
 

benbenrf

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Hi KWJDECKER

In a completly different price bracket - this would be an "antenna for life" (i.e. you'll never have to, or will want to, replace in with any other general purpose broad bandwidth 20Mhz - 1.4Ghz antenna) - is Rhode & Schwartz's HE309 + PSU (power supply box - which can run off mains ac or 12vdc).

I have, and use, HE309's daily - both at home and in mobile situations - as well, they are used in Afghanistan (SIGINT). For mobile config I re-modeled the round glass fibre enviromental protective cover - binning it to replace it with a homemade blade profiled shape (good for 70mph-80mph on a decent magnetic base).

The 309 comes in 2 configs: active or passive (I have examples of both).
The passive is quieter (as passive antennas tend to be) but no-where near as flexible & versitile as the active version is. New & out the box, R&S won't give you much change for an an active example + PSU out of $10K - I think they retail for around $8K. If you have the skills, then build your own PSU - nothing to complicated about it, but it'll have to be dead dead quite and smooth. Can't stress enough the importance of designing out component and mains "noise" & "hum". Get this wrong, and - well, the money invested in the actual antenna element part becomes a waste. Like a baby with it's milk bottle; HE309 performance is completly dependent on the performance of it's PSU.

Whats a used example cost? around $600 - $700 - and with the R&S PSU for just under $1K.

Caution regards buying used: buy from someone you are comfortable with/know/can get a test cert from etc etc ..... else, if at all poss - try see the unit first.

No harm taking a spectrum analyser/tracking gennie/signal source (and whatever other test instrumentation you can get your hands on) with you - Check to see the antenn its self has/or has not been modified: examples with a FISINT background will almost certainly have had part/s of their active circuitry "modified/customised" by the previous "owner" - more than likely one or other of the "3-letter" abbreviated Government agency/department.

The length of the active HE309 glass fibre tube is taken up with mil-grade pcb's, section/circuit shelilding, ic's and custom gain related circuits. These examples are supposed to be shredded and not on the used/open market, however, I know they do turn up from time to time on eBay, specialist trade mags and shows - and almost certainly if the seller is a private individual, they won't have a clue. Don't buy - unless you understand the modification made and it's going to provide you with the performance you want/need e.g on the R&S website you will find, I think, a PDF chart showing Vertical rad pattern for different freq's across the entire HE309 op-bandwith. Notice the relationship between Gain and the Vertical rad pattern i.e. how the shape of the Vertical rad pattern changes, to the point where around 1Gig it starts to break up into "spears". No big deal here - typical of active antennas with a similar Gain/bandwidth design spec - however, used examples which have been "customised" for specific applications, and a fair amount of them have been - may well demonstrate (as one example of customisation amongst many others types) very very different Gain or Vertical rad pattern for a specific freq or bandwidth within the op-bandwidth, at the expense of performance on/at other freq's. I have modified a couple of 309's is this respect - to get a specific RX rad pattern/Gain for a specific freq or bandwidth - but, but: it is ALWAYS optimisation for specific freq's at the expense of performance elswhere over the antennas' op-bandwidth. It is unavoidable and will mean that you could poissibly land up with an antenna partially or completly deaf just where you would like it to be performing at its best.

I can't help feeling that although R&S don't say anything about this anywhere in literature related to the 309, or anyhwere on their website, the the HE309 antenna was designed specifically with such types of end-user "modification or customisation" in mind.


If buying used you want to check that noise & gain figures are as they should be across the op-bandwidth. $600 - $700 bucks is a fairly substantial amount for an antenna - any antenna - but as said earlier, you are getting a substantial box of tricks for you rmoney - which does what it says on the tin, and does it very well (in my humble opinion)

If you'd like some photos of the "insides" of the glass fibre tube and the psu box, happy to send you some - there's a fair amount of electronics inside the tube (boths sides of the pcb and quite a bit more than can be seen on the website picture/s). The PSU is well designed and built with top-shelf components throughout. As broad-bandwidth antennas come (and go), the HE309 is as good as they can get in terms of reliability & construction, but most importantly: performance - isolation is excellent and the gain stages are as quiet as one is likely to able to get their hands on - short of throwing money at "lab grade" amp stages.

Any questions(?) - ask and I'll do me best to answer.

In summary: give the 309 some consideration if your budget can stretch to it. It's a jolly nice broad-bandwidth omnidirectional antenna - both for use in a fixed enviroment (i.e homebase), or as a mobile antenna (with modified glass fibre cover).
 

mcradio72

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yeah agreed that's not what I am looking for either. To get an idea please look at the link above in my first message.
 

benbenrf

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Not far off $8k if purchased new from R&S - but as explained, you can pick them up used for around 10% that cost (+/-$800) - and even less if you can build (or find someone to build a PSU you for you). Still not cheap but add up the money many enthusiasts spend of say over 5 - 10 years on antennas, and suddenly it's not expensive.

Around 4' in length - yes, and quite bulky.

They are used in mobile situations, though granted, in the standard glass fibre shroud look pretty silly on a car - which was why I explained the glass fibre shroud they come in can be replaced with a home-made oblong shaped fin shroud which would retain the 48" but be around an 1" x 3" at the widest points.

Not covert or discreet, but any more intrusive than a bunch of aerials, which is what you [will] otherwise need to enjoy anywhere near decent 20Mhz/25Mhz - 1300Mhz coverage, or a car with HF aerials? - a matter of personal opinion.

The reality is that to achieve anywhere near decent 1Gig plus Rx coverage off a single antenna means that it is going to have to be active. I know folk say, "ahh, but with my passive XXXXXX antenna I can hear right across VHF/UHF bandwidths just fine.....". They think they can - untill compared side by side with a properly designed active antenna folk don't realise how much they are aren't hearing.

There is of course a potential problem to using any antenna like a 309.
Irony is, using it with most off-the-shelf Radioshack/consumer type scanner/receiver chances are one could/will experience even worse reception than otherwised experience.

Why/How? - the large majority of sub-$1k off-the-shelf scanner/receivers today just do not have rf front ends & 1st stage filters capable of the seperation & selection required to handle the volume of rf traffic even an off-the-shelf resonant passive antenna provides - let alone an active one.

Anyhow, it was just another option for you to consider.........
 
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