BIG BIG NEWS!!

That ISS SMR appears to be an eton/Grundig G8 Traveler II. Retail price is $60. Here's another link I found to a page on the ISS site: http://www.theradiosource.com/products-smr-receiver.htm

Also, here is a link to the G8 info available on the eton site: http://www.etoncorp.com/en/productdisplay/g8-traveler-ii

I am guessing what you get from ISS for $143 is the G8 radio along with documentation containing a table or graph to convert the G8 "dBu" display value to the value in "dB volts per meter" that you would see on a Potomac FIM-41 in the same exact location.

Apparently, but only implied, is that ISS has determined the G8 reading is repeatable across a random sample of production G8 radios, or they provide a custom correlation chart/graph for each SMR radio they sell. Either is possible and viable at their $143 price.

There have been discussions here previously that suggested ways to approximately calibrate the readings from radios that have an "S meter" indication. Possibly, ISS is the first source to actually do such a calibration.

It would be a fun and useful project for someone who owns or has access to a calibrated FIM-41 to do a careful conversion chart for the G8 and publish the results. Otherwise, $143 to ISS is a reasonable and affordable price.

From the picture included in the link in Post 1 above, this "compliance appliance" appears to be an ultralight, multi-band receiver based on the Silicon Labs Si4734 DSP chipset.  Such receivers are manufactured in China, and available by direct order from various Hong Kong distributors for less than half the price mentioned in that link.

Carl, in this category you are ahead of most of us, as from what you have posted here you already own such a receiver (a Tecsun PL-310).

Unfortunately, such receivers are nowhere near the equivalent of the Potomac Instruments FIM-41 nestled by the right arm/hand of ISS Project Manager Tom Coviak shown in the picture in that link.

The FIM-41 is a lab/professional instrument calibrated to a stated accuracy when measuring known field intensities.

Inexpensive receivers using a "loopstick" receive antenna and an Si4734 DSP chipset are not calibrated to measure actual field intensity.  They provide an uncalibrated/uncertified indication of relative field, only.  In other words, they show changes of field intensity, but do not show the real values of those field intensities (in µV/m, mV/m etc).

FCC §15.209 and §15.239 give the legal limits for field intensity for unlicensed AM and FM broadcast stations, in units of µV/m.

So the (bad) news is that inexpensive, DSP-based receive systems similar to the Tecsun PL-310 cannot be used to prove compliance to those limits.

The comments registered by PhilB and Rich are exceptionally interesting with regard to the Big News unveiled in this thread. Thank you for both.

Whatever the outcome, I'm going to bite and place the order for this instrument, and use it side-by-side with my TECSUN PL-310, which was first suggested by Rich, and which I cherish as a signal monitor.

In the Part 15 world perhaps show is part of the game, and if we tiny stations make the attempt to be compliant, perhaps the huge government over-power will view us as "friendly."

It would be a fun and useful project for someone who owns or has access to a calibrated FIM-41 to do a careful conversion chart for the G8 and publish the results.  Otherwise, $143 to ISS is a reasonable and affordable price.

An accurate conversion chart for such DSP/loopstick based receivers needs more than a calibrated FI meter such as an FIM-41.  It also needs a means to generate a known field intensity across the measured r-f spectrum.

If so calibrated (which may be unlikely), the $143 ISS price for their SMR would be exceptionally low -- given the commercial engineering and documentary cost needed to do that with accuracy acceptable to the FCC.

Caveat emptor?

Carl, before you bite, you should send them an email requesting technical clarification. Their web site doesn't provide any meaningul information. Ask them if they provide correlation of the G8 reading to actual FCC measurements and how accurate are the results? In particaular, will you get a calibration chart and how accurate is it? Tell them you represent the Part 15 AM intrests and this could be a significant markert for them. Be sure to post their reply information for us all.

Otherwise, if you just place an order, you may end up with a G8 at over double the price to add to your collection.

Thank you for the advisory.

Yes, I will tarry a bit and ask for more clarification and documentation.

Be this all as it may, it is highly interesting as Part 15 life goes.

If ISS is going out on a limb, are we thinking they may be self-decieved?

I agree with caveat enotor!

An accurate source is not necessary when you are comparing a calibrated FIM-41 reading to the G8 reading. The only important factor is that you record a measurement of any stable signal on the FIM-41 and then record a reading from the G8 after replacing it in the exact same poison that the FIM-41 occupied. The "any stable signal" can be a standard broadcast station during the daytime. As long as it's reading on the FIM-41 doesn't vary significantly, it's stable enough.

The FIM-41 claims a 1% accuracy. Even if the correlated G8 accuracy is only 5% or 10%, it will be good enough to judge whether a transmitter/antenna is close to the trigger level that would cause the FCC to scrutinize your transmitter/antenna more closely or just drive on by.

RE: ISS Field Meter Questions

Thank you for the advisory.  Yes, I will tarry a bit and ask for more clarification and documentation.

Might better responses from ISS on this topic ensue from enquiries to them from manufacturers of Part 15 AM transmitters/kits, rather than from a single "Part 15" operator as suggested by PhilB?

i'd rather just stay quiet about this one and refrain from spending that 140 on splitting hairs. if the final is a small-signal transistor like a 2n4401, 2n7000, 2222, etc. i figure its close enough

Instructions : manufacturer; ISS guidance sheets for the use of SMR

Receiver for AM noise and signal monitoring.

PhilB wrote:  I am guessing what you get from ISS for $143 is the G8 radio along with documentation containing a table or graph to convert the G8 "dBu" display value to the value in "dB volts per meter" that you would see on a Potomac FIM-41 in the same exact location.

Below is part of the reply about this to my e-mail to ISS about the SMR...

> -----Original Message-----
> From: Richard Fry
> Sent: Thursday, August 01, 2013 10:54 AM
> To: XXXXXXX@theradiosource.com
> Subject: ISS "SMR" Signal Measurement Receiver
>
> Hello -
>
> Are the specs for this device available on line? If so, could you please
> send me the link?
>
> If not, could you please tell me the range of AM broadcast band field
> intensities it can measure, and with what accuracy for a known field
> intensity in mV/m? Is the antenna built in to the meter case? What kind
> of antenna does it use (loop, loopstick, etc)?
>
> Can you confirm that the output indication of this meter shows field
> intensity in units of uV/m, mV/m etc, and does not show just a relative
> (uncalibrated) indication of field intensity.
>
> Thank you.
>
> Richard Fry

REPLY

>>See the attached. If you have remaining questions, please write back!

>>  (the unit is not calibrated, of course, just a good reliable relative measure.)

Appreciate Rich collecting information about this G8 radio from ISS.

"..Good reliable relative measure" sounds good. How good is it?

Is the TECSUN PL-310 equally good and reliable?

">> (the unit is not calibrated, of course, just a good reliable relative measure.)"

Wow, that's not at all what I expected. The ISS site says: "The SMR Receiver provides a digital LCD readout that correlates reliably to scientific measurement equipment…for about one-hundredth the price." There's also the picture on the right showing the guy holding the G8 next to a Potomac FIM.

This is quite misleading when, in fact, the SMR is really an uncalibrated relative field strength meter. When you read their words carefully, I don't think there are any absotutely untrue statements. The wording is just misleading. It would all be clarified immensely if they just state that it is a good relative field stregnth meter.

I guess you could say it has an advantage over many of the cheap relative FSMs because it has a digital readout and is tuneable to reject other frequencies.

In function, it is equivalent to most any MW receiver with an S meter. The digital display makes it much more precise compared to a cheap analog meter.

It's a real stretch to say it compares to scientific instruments costing a hundred times more.

The eton/Grundig G8 or the Tecsun 310 would appear to serve as very good inexpensive relative FSMs, good for tuning an antenna and monitoring for changes in field strenth. The precise location and orientation (loop antenna) would need to be repeatable if you want to monitor for long term changes in siganal strength from the antenna.

This radio could be a good indicator of compliance. 250mv/m = 48dBu approx. 1000uv/m(Canada rules) is 60dBu approx.
So if you replace the stock antenna with a 1 meter length of wire or other telescopic antenna and stand 3 meters from your transmitter on the FM station you are transmitting on and read no more than 48 dBu you are not exceding legal limits.

Mark