Well, shortly after posting something about not finding the much more limited range of our legal FM transmissions to be very inspiring, what have I gone and done? I bought not one, but two Decade MS-100's!
It all began with me dragging out my EDM transmitter recently, and firing it up on the lowest power setting. I quite liked having a signal on the FM band, and even thought of simulcasting my AM signal, which is on air 24/7. Trouble is, I don't feel comfortable about doing it with a transmitter than is not certified. I don't have a problem using a non-certified transmitter on the AM band, as it would be fairly straightforward to show a schematic to a visiting FCC Field Agent, and describe how I know the final has a DC power input of no more than 100mW. Lacking an accurate calibrated VHF field strength meter, I would have no way of showing that I am in compliance with FCC 15.239 on the FM band.
It was at that point that I decided to look around for a Decade MS-100. I couldn't justify the cost of a new one but luckily, the used ones sell for a lot less than the new ones. A LOT less. I came across a metal enclosure version in excellent condition, with the AC transformer, for just US$60 including shipping, which is even less than used ones normally list for. Score! It arrived yesterday, was indeed in great condition, and worked perfectly. I am very happy. So happy in fact, that I immediately ordered the other MS-100 the seller had. This other one is the version in the plastic enclosure, also in excellent condition, and also $60 including shipping. I already have plans for it.........
My question is this. On the one I received yesterday, I noticed that there is a small hole on one side of the metal enclosure, through which the power adjustment can be accessed. If you wanted, you could adjust the output power with a jewelers screwdriver without having to take the top off. It strikes me as a little odd that in a certified transmitter, the power adjustment would be so easily accessible. I'm wondering if perhaps when it came new from the factory, there was a sticker over that hole, with some kind of a warning not to remove it. Do any MS-100 owners have anything like that on their units? There is no sign on mine that there was ever a sticker or plug over the small hole.
The range I am getting from it seems in line with what I would expect for a unit intended for the US and, lacking an accurate field strength meter, I'm leaving the adjustment well alone!
I am a user of the Decade Ms-100 as I am on FM here in Canada. The plastic cased ones in the off the shelf Hammond cases are older models. The metal and much heavier ones in the steel cases are newer, but the only changes were the audio input on the back for a 1/4" TRS.
They didn't always come with the hole to access the power adjustment....that seems to be on the more recent productions. They are certified BETS-1 in Canada and FCC part 15 in the USA and BETS-1 is higher power than the FCC part 15 and they are adjusted when sent out to where it is being sent to. Maybe he did that to make it easier to not have to take it apart to do the adjustment. That is a good question about the access hole! I was thinking of asking Decade myself but yes you have a point that a certified product should not make it easy to access the RF adjustment. In fact now I will call or email and ask about that!
I will post the answer I get.
By the way, you "can", without any mods or adjustments to the transmitter at all, so no voiding certification, put the Decade on a metal surface e.g. metal table, line the shelf with tin foil. A metal surface will enhance signal off the antenna creating a ground plane.
I would take a ride around and make sure your signal is not traveling some extreme distance. If it's staying within a block or so and not splattering or anything then I wouldnt worry about it.
But of course you know that.
@mark - that's a useful bit of advice about increasing the potential range of the transmitter without any internal mods to the unit. I'm thinking that when the transmitter went through the lab testing for certification, and also when it was adjusted for compliance with either BETS-1 or FCC 15.239, there was no ground plane present. Strictly speaking, adding a ground plane underneath the transmitter could increase the field strength at a given distance from the antenna, putting the unit out of compliance.
That said, although it could provide a useful boost to the coverage and range, the improvement in signal strength wouldn't be orders of magnitude greater. Intentional pirates are running powers that are several orders of magnitude greater than what is needed to comply with BETS-1 and FCC Part 15 regulations. I guess what I'm trying to say is that there is the letter of the law, and the spirit of the law. Adding a ground plane might put you out of compliance with the letter of the law, but many might still consider it within the spirit of the law. A reasonable inspector would (hopefully) conclude that the difference between a Part 15 station that covers just one small apartment building, and one that covers half a block, or a whole block, is not anywhere near as concerning as the pirate who has a solid coverage radius of a mile or two.
I was wondering about the plastic vs metal enclosures. Google didn't help me in that regard, so thank you for the info Mark. I'd like to experiment with mounting an MS-100 in a weatherproof enclosure outside. The one with the plastic enclosure would work well for that. I'm thinking along the lines of mounting the whole thing, enclosure and all, inside a bigger weatherproof housing.
Yes @richpowers. I already took a walk around the block. Am feeling pretty comfortable with the coverage. It doesn't take long to drop out, but it's a solid signal in all the common spaces inside my 10 unit building. From that, I'm guessing that it's easily receivable inside all the individual apartments too.
I really like this transmitter!
@rugster No difference between plastic vs metal except the metal may have better shielding. The plastic ones came with a conductive coating on the inside so there could be chassis grounding.
As for the surface you place it on, The labs test is on a wooden table in a special room with no RF reflection. An anechoic chamber. As a user, if you put it on a metal surface, table, metal shelf or filing cabinet, whatever, you are in no way changing the design or "modding" the transmitter in any way. I can't see certification not valid and nowhere in the rules does it specify what surface it must be on. I mean, that's a bit too unrealistic.
@mark, in the thread about the SW200, you wrote,
"As for the Decade if you got one with the access hole used on Ebay, do you not think that it has already been adjusted by someone else? What is the first thing someone that gets one would do with this? Right! And it's a pot like the Schlockwood output adjustment, not a normal one but a trimmer that takes about 15 turns either way from low to high. If someone turned it the wrong way it would lessen the output not increase it.
But yes I have emailed Decade and awaiting an answer."
I didn't buy it from eBay, it was through the Sweetwater used gear exchange, but same difference. Yes, that's my concern - that an access hole makes it too easy to adjust the output power; especially if it's not covered by a factory sticker. I am curious as to how much adjustment range there is on that 15-turn pot.
Interesting info about the certification test being done on a wooden table. As I said, I think that any improvement or increase in coverage/range gained by placing the transmitter on a metal surface would not be enough to concern an FCC Field Agent, or the Canadian equivalent (my apologies - I don't know what they are called).
I'm keen to hear what Decade will say.
I never would have considered that a Decade FM transmitter could be found at Sweetwater. I know I bought something through them a long time ago but cant recall what it was. Forgot all about them till you mentioned it.
Back in the day I put a Decade inside a weatherproof box, and installed it on the roof of the storefront I was operating from. The store was also on a hill, so the transmitter was pretty much line of sight to everything, and the range was certainly increased. Obstructions can really hurt FM range.
I've never seen any Decades with holes to the power adjustment pot. I too am looking forward to Mark's email.
@rugster To answer your question "I am curious as to how much adjustment range there is on that 15-turn pot".
Not much. The max according to the specs is 1.1 milliwatts max power into the telescoping antenna that is adjustable as per certification to 1/4 wave length of selected frequency. Which is a little above BETS-1 allowed power. Even from Sweetwater same thing. If users see an RF adjustment you know it's been adjusted by someone who used it.
If users see an RF adjustment you know it's been adjusted by someone who used it.
I wouldn't take it as a given but yes, it's a distinct possibility.
That's another item to add to the want list - a digital storage 'scope, with 200MHz or greater bandwidth. I'm curious to measure the peak to peak RF voltage across a 50 ohm resistor placed across the output of my MS-100, to see what the output power is. That should give a strong clue as to whether the power adjustment control has been messed with.
Here's a recent one on an Ebay listing and you can see the access hole on the left side looking from the front.
https://www.ebay.com/itm/365122994637?_skw=Decade+MS-100+FM+transmitter&epid=721160210&itmmeta=01JH2BZKEG30PBDVZC6XGKV1C0&hash=item550306c1cd:g:1xwAAOSwdytivHPa&itmprp=enc%3AAQAJAAAA8HoV3kP08IDx%2BKZ9MfhVJKnjn5qHcjPLcRpGCpLjdPUZ9Ggho8sy9zIjtS53Vigj15rpmthklHmCKE%2BDesCWyCIMk7Uph3ccTJ9%2BSIhUwT0JV9hw1Em3PY8t63HIrj%2F4pKmmHAC5rc%2FGORSgiQbRyFOOlOEDHLGIWhBCVdlCDtyo3ywgJizBLF6cXtKwwsMDywH2VXRnUFyu82nZ1SxBMHsdQ70cF9B9znX0HeZY7aK%2BOt53%2F81kV60wafz1s5%2Bz%2FtFkBl8v0fmDP3dU04YIdOEh6P6rMGeuho%2FOlSAzqFaO9IxrUMpG3vYru%2FNEI44%2F9Q%3D%3D%7Ctkp%3ABFBMsLf-y4hl
I recently purchased a new one sealed, never been opened from a electronics dealer here in Toronto, AV electronics, that carries them and had one on a sale price(well 10% off the $525.00 regular price) and from a sealed box brand new product the hole was there, got it a couple of months ago but I don't know how long it was in stock at the store. No cover or warning not to touch. The hole was as you can see is as the metal case was manufactured. I am awaiting his answer with interest also!
@mark I find the "ebay Refurbished" caption above the title curious. I've never seen that said before, but have seen "Seller Refurbished" captions numerous times.
Looks like a real nice unit and not a bad price either, but not nearly as inviting as Dave's $60 scores!
Wow.. there's a lot of Decade transmitters up there, at least one as low as $60. Not that I'm presently interested, but it's good to know they are plentiful.