Comet SMA-3 *perfect* for my Whistler's front-end

[nanZor]

I live in the rf-jungle of Los Angeles, and my Whistler 1040 (long lineage to the RS Pro106) has a hard time, especially since I'm plagued by a pager on 152.360, along with a lot of other fire-breathers. My Uniden 396xt handles it better - but still no amount of antenna-juggling and attenuator settings were entirely satisfactory.

By chance I found an old Comet CH-32 "miracle baby" 1-inch duck tuned specifically for the 2m/70cm amateur bands. You can see the write up on that here:
https://forums.radioreference.com/s...-32-miracle-baby-saved-my-1040-500-106-a.html

Since it worked so well, I took a chance on it's bigger brother: the Comet SMA-3. Basically the same dual-band 2m/70cm amateur tuned duck, with 800-960 mhz rx-only resonance. Like the smaller version, resonance isn't the only important factor - NARROW TUNING is what acts like a bandpass / band-reject filter, which the Whistler (and even the Uniden) benefit from. For my Whistler, I had to use a bnc-to-sma female adapter.

Examples compared to even the canonical "RS 800 mhz duck":

** RS 800 Duck **
PAGER Firebreather on 152.360: Full strength overload
NOAA Wx: Full strength overload

** Comet CH-32 Miracle Baby **
PAGER Firebreather 152.360: GONE
NOAA Wx: GONE

** Comet SMA-3 **
Pager Firebreather 152.360: 2 bars
NOAA Wx: 2-3 bars

** ALL OTHER DUCKS including other 2m/70cm amateur dual-banders **
Similar to RS 800 Duck. That is, even though resonant on other bands like 220 or my beloved Icom airband duck, pagers and noaa just blow right through, making the front-end noisy, *especially* up at 927mhz where I do amateur repeater monitoring.

My interest in 927mhz amateur repeaters led me on this journey. It is even harder than 800mhz comms, which for the LAFD is so strong that it was hard to tell if I was making progress or not. But 927 amateur repeaters, along with it's own inherent band noise? Wow, what a pita.

No amount of antenna juggling and attenuator settings was really satisfactory from my 20 years of duck collecting. Yes, the Uniden 396xt coped much better than the Whistler - we all are aware of that. BUT NOW, with the Comet's, I am finally at the point where I can clean out my "duck drawer".

Although the front-end was tamed by the tiny CH-32 miracle-baby, and makes a great 800-960 rx-antenna on it's own, the very narrow tuning meant that I couldn't even hear out-of-band comms, which I sometimes desire to do without swapping out antennas all the time. Not convenient.

Could I find a middle-ground? YES. The longer Comet SMA-3 has the same narrow-band tuning for the 2m/70cm amateur band, but is long enough to allow for reduced sensitivity reception of out-of-band comms, but still have enough attenuation to keep the Whistler's front-end clean. I'm stoked. Note that other 2m/70cm amateur dual-band ducks may be resonant too, BUT they may not provide such tight out-of-band impedance attenuation as the Comets currently do. (at least these two models - I haven't tested the entire line.

So if you live in an rf-jungle, and are trying to cope with a Whistler / GRE / RS front-end, or even want to improve your Uniden (my 396xt showed a slight improvement too!), then having both the CH-32 and the SMA-3 in your bag to my mind, would be all you'd need.

The moral is that just because an antenna is "resonant", or is touted to be "able to receive xxxx to xxxx mhz", does NOT mean that it is narrowly tuned, where that benefits a scanner front end. A paper clip is also broadband, but it too FAILED in my situation. Only narrow-band tuning saved the day for me in the jungle.

Ok, I could do without the hinge in the middle gimmick, but I can live with it. Might be useful for other scanners that are primarily horizontal in operatin.

 

[nanZor]

Quick synopsis of Comet SMA-3

How about the short version:

The Comet SMA-3, like it's baby-brother, the CH-32, is primarily aimed at amateur radio 2m/70cm transmit up to 10 watts, with 800-960 mhz rx only.

Go about 10 mhz above or below the amateur bands on vhf or uhf, the attenuation gets progressively worse very quickly. Example:

LASD on 483-484 mhz - severely attenuated, or just gone completely with the CH-32.
220 mhz amateur repeaters - the same.
Above 150 mhz - same.

Basically Comet's rx-only bandspread specs are pretty much accurate. Some manufacturers spout specs on their antennas that can compare with a paperclip's broadband response. These Comets seem to be the real deal..

If your scanner has a hot front-end, and/or lacks extensive bandpass filtering, these narrowband responses help tame the front end. This may be preferable to the typical alternative of just activating an attenuator, which doesn't always work well enough with it's over the top hammer approach.

Of course one could always tack on some sort of external bandpass filtering, but the Comet's may be all you need or be more convenient before you get to that point.

 

[nanZor]

Not biased

Heh, just to prove that I'm not a schill, let me say that not ALL comet antennas may be the best choice for an rf jungle environment.

Example: Another tri-bander, the HT-224 is designed for 146/220/440 mhz amateur operation primarily. Very handy with my triband transceiver.

However, with my scanner, the firebreathing pager on 152.360, NOAA and numerous other sources blow right past the HT-224 to the Whistler's front end, making my 800/900 mhz reception noisy.

So: Comet SMA-3 vs Comet HT-224 for scanning 800/900 mhz band? Comet SMA-3 hands down.

It is a pretty easy test if you have a drawer full of ducks. Even if you are not in a strong rf-environment. Just do a quick scan for typical troublemakers like pagers or NOAA WX and compare to see which ones receive them, and which ones don't - or attenuate them to a significant degree. If your radio can receive the FM Broadcast band, try that too - another known troublemaker for some, especially airband enthusiasts not using the Icom duck.

 

[vagrant]

I use various PAR filters myself to notch out or band pass as needed. PAR Electronics | Filters for the commercial 2 way market, MATV, FM broadcast, laboratory, marine industry, amateur radio, scanner and short wave listening enthusiasts

I believe he sells a filter under the Amateur line that handles your 152 pager problem. Attenuation from a compromised antenna is not my friend, but I understand your point.

 

[nanZor]

As an airband guy, I have the PAR FM broadcast notch filter myself. Outstanding.

Many who choose the $5 online cheapies may not realize that they don't cover much of the band, and not do any notching at all on their problem frequency - other than inline insertion attenuation. So yeah, HIGHLY recommend the PAR line of filters.

One big advantage to the very narrow Comet SMA-3 is that there is an overall reduction of troubling frequencies, not just one problem child like the pager. The overall effect is that aside from total desense, the *overall* noise floor is lower.

This is what I think the engineers at Comet were trying to achieve with the narrow tuning. Lowering the noise floor from broadband receivers (Like a Yaesu VX3 and others out of band) makes the dinky antenna sound better than it is! Especially when it is so bad that it affects the 800/900 mhz reception.

But yeah, I'm with you. One other trick suitable for desktop use if you don't have specific filters handy is to put a multiband di/triplexer inline, put a 50 ohm load on the unused ports, and go that way - as long as you are within the passband of the triplexers port. (Note - my 800mhz reception on a Comet triplexer passes through the port limited to 510 mhz really well) -- anyway getting far away from the topic.