Need some antenna advice (for my CM15A, of course)

The input impedance of the RF receiver module is 50-ohms as is the output impedance of the eggbeater antenna. Using the recommended Digikey BNC connector and 50-ohm coax (RG58/U) is optimum. 25' & 50' pre-assembled

50-ohm cables are readily available on the web. TV connectors & cable are 75-ohm so there will be a mismatch. However, this is probably not critical.

Any external antenna is likely to be an improvement over the internal antenna but the eggbeater should give the best results. However, the TV antenna may give adequate range - especially if you use the preamp.

There are numerous tutorials on soldering available on the web. The important thing is to use a low wattage soldering iron (15-25W).

You can c>Hi everyone!

Thank you very much Dave, this is great stuff.

I have a little component here, and I wonder if this will help me at all.

It is a "VHF/UHF/FM Separator/Transformer"

The input is coax, and it has three outputs:

1 - two screws for FM (looks like I could hook up my round antenna onto this

2 - two wires for VHF, and two for UHF.

I noticed that inside the box, it has a few resistors.

If I were to plug my coax cable running from the CM15 into this little box... should I hook up my round antenna to any output in particular?

Perhaps this box is useless. It just seems like the perfect little thing to go between my CM15 and the antenna...

Thanks!

Mike

Your "little box" will do more harm than good. The preamp is all you need between the CM15A and antenna.

I should note that the TenTec 1001 preamp should be powered with a 12V _regulated_ DC supply. You can f>Thank you very much Dave, this is great stuff.

Thanks again for the advice, Dave!

Okay, I will not use those boxes!

Good call with the regulated DC supply.

Of course, first I have to solve more elementary issues... like figuring out if it makes a difference which way I pop in the resistors, and whether the main amplifier piece is placed in the board with writing side up or writing side down...!

I'm sure I'll figure it out!

It's all on my to-do list for this weekend. Should be a fun project!!

Mike

Hi Dave!

You are correct...! The documentation clearly mentions that dot, and where it goes.

If, however, the dot touches the board (dot side down), then it will affect the other pins. If the dot it upwards, then that matters, too. I assume one should see the dot when one places it in the socket.

I'm going to bring the whole thing to my local electronics store. They'll probalby laugh at me, but hey.. there's a first time for everyone, no??!

Thanks again!

Excellent!

I think I am going to give this a shot today.

Last night, I hooked up my CM15A to an old, round TV antenna. It's only about 8 inches from edge to edge. I stripped the BNC cable and attached it to the two antenna leads.

Surprisingly, every [non-slim] remote and module works in the house, from the top floor to the basement, where the unit is located.

As far as the slim X-10 remotes go... I am having problems in many rooms.

I hope that this amplifier will solve everything!

Thanks again for your help!

I forgot that you have to form the leads. I've been using a surface mount version of the amp.

It's dot side up.

That's for a higher frequency than the 310MHz so, like I said earlier, it's less than optimal. If there's only one loop, there's also an impedance mismatch which is also less than optimal. And, with a single loop it's more directional than the eggbeater. You might try rotating the antenna 15° each day or so until you find the optimum orientation.

If not, constructing the eggbeater probably will.

Hi again!

I have a few remaining questions and clarifications! Sorry!

I am heading to the biggest electronic store in the city this week (Finally!) So I just want to educate myself before I head out there!

1 - If a cable is RG58U, does that mean it's automatically 50 Ohms? I have some RG6 cable here, and one is labelled as 75 Ohms, so I know that's not optimal, as you mentioned. If, however I find RG58, then am I okay?

2 - How bad is it to use F connectors instead of BNC connectors? It seems like I have so many of these things lying around, and I have a crimper and all sorts of accessories in my workroom. Can I put F connectors everywhere instead of the BNC ones?

3 - For the phasing line, if RG62 (93-ohm) coax is not available, what type of coax would you recommend as my second and third choices? Will I then have to cut it longer or shorter to compensate?

4 - Is there any trick when it comes to dealing with the ground part (the shielding) of coax cable? I just kind of strip it, and twist up all the little threads and tin them. It looks silly, but is that the correct thing to do? It's a little challenging soldering the thin coax cable they send with the kit onto the board. I'd love to just solder some type of surface-mount F connector right onto the PCB. In the picture on their website, it has that. this just cable with one foot of cable. Soldering it on is a problem. Advice is welcome!

5 - Must the TenTec Amp be placed as close as possible to the eggbeater, or can I mount it down by the CM15A? Intuitively, I'd think it has to be closer to the antenna, but perhaps not. I'd love to keep the amp near the CM15A. Your thoughts?

6 - Is there a limit of length for the coax between the CM15A and the eggbeater? I would love to leave the CM15A here in my basement, yet run the coax up the side of my house, and place the antenna in my attic. Is that okay? (This is why point #5 is also important. I have no problems running coax up to the attic, but I'll have no power for the power supply!

7 - Last, but not least, from a physics point of view, is this the best type of antenna to construct? I know other companies make antennas for this sort of thing, but they are straight. Also, my old transceivers have those telescoping ones (I actually attached larger ones), and they work like a charm. Is the eggbeater style truly the best possible shape?

And that's it!

Thank you so much for all your help. I hope that other amateurs can benefit from these tips.

I hope that with answers to these questions, coupled with the article and all the other posts, I'll be able to walk into the electronics store nice and informed, and then build the perfect antenna!

Thanks!!

Mike

RG58 is 50 ohm; RG6 & RG59 are 75 ohm. 50 ohm is optimal in this application.

F connectors are 75 ohm. 50 ohm BNC is optimal in this application.

75 ohm coax would be the next best choice. Keep the length as stated on the web page. The nominal impedance of a loop antenna is 100 ohms. The phasing line is intended to match the 100 ohms as close as possible. The loops are mounted perpendicular to each other. The signal from one will be 90° out of phase with the signal from the other. The phasing line (length=wavelength/4) acts as a delay line to bring the signals in phase. The two 100 ohm loops are connected in parallel so the resulting impedance is approximately 50 ohms which matches the 50 ohm RG58 coax.

I use an awl to debraid the coax, twist the strands together and tin with a soldering iron.

I just use a couple of short pieces of hookup wire to connect the preamp to bulkhead type BNC connectors. It's not optimal but...

In theory, the preamp should be at the antenna. In practice, it works fine if it's near the CM15A.

The length of the coax (within reason) is not a factor. Your proposed setup is fine.

There are about as many antenna designs as there are fish in the sea. A lot of people have used a turnstile design made from twinlead that I documented a few years ago. The advantage of the eggbeater is that it is easy to build, is omni-directional (more or less) and has 50 ohm impedance (so no balun is needed). My tests have shown it to be measurably better for this application than the telescoping monopole, ground plain, turnstile, Lindenblad, and other DIY designs. Eggbeaters are widely used to receive data from weather satellites.

However, environmental factors may influence reception. IOW, YMMV.

Hi Dave,

I just wanted to say thank you very much for the in-depth reply to my questions!

I read your post about five minutes after you posted it, but I just realized that I never said thank you.

Thank you!

I hope to get out to the electronics store this weekend. I can't wait to wrap up this project!!

Mike

Hi Dave! I have almost all the parts!

Question for you!

1 - How do I know what type of Power Supply to get? I have a whole bunch of old 12VDC from old calculators and stuff, but each one has differnet MA ratings. What do I need so that this thing works, but so I don't fry it?

2 - Can I assemble everything (Antenna == Pre Amp === CM15A) Even if I have yet to get a power supply? Will that decrease my signal?

I am looking forward to moving ahead!

Thanks again!

Mike

Darn, I hate this text editor. This is the second time I typed a message today and I lost it. With most other forums, you just have to hit TAB to get to the POST button, and then spacebar to hit it.

With Google groups, TAB brings you to Cancel.

When will society learn to standardize user interfaces a bit more??

In any case, thanks for the info!! very interesting datasheet there! You are right... that is a sophisticated little device.

I just surfed the Jameco site. Tough to find adapters that spit out only 25mA.

I will call them tomorrow and get a part number.

I'll also see if TenTec recommends a specific power supply.

ALmost there!!!

Thanks!

Mike

Jim wonders: Why are you concerned with an adapter that is limited to "only 25 ma.". Remember the critical issue is how well regulated the adapter supplies at the voltage you need with the load you are supplying with your device. If the regulated voltage needed by your device is supplied by an adapter that would supply that same voltage at a 2.5 Amp load, it will work fine on the 25 ma device and even 100 of the same device in parallel.

1. Way, way, way back I recommended you get a REGULATED 12V power supply from Jameco. Current requirements are low (~25mA) but the regulated voltage is critical. That little 4 pin preamp is a very sophisticated device. Read the S001 Application Note (Basic MODAMP MMIC Circuit Techniques) at...

1. You will likely get lousy recepti>Hi Dave!

25ma is the MINIMUM to look for - there is no maximum. Most will be 500 -1000ma and will be fine. It's not that the adaptor puts OUT that much current as much as it will allow your device to DRAW up to that amount as needed. If it only draws 25ma then that's all you'll use. Pretty much ANY regulated 12vdc adaptor will do the trick. Regulated adaptors are typically supplied with CCTV cameras.

From:Michael G. snipped-for-privacy@gmail.com

The MMIC used by TenTec is made by Minicircuits. They also have an app note on biasing (but for a slightly different range of MMICs) at...

http://www.m>Darn, I hate this text editor.