- June 27, 2020 at 7:56 am #115244
Right here I go. I need advice. I have ‘six of one, and half dozen of another’ as the saying goes. I’ve lots of kit and facilities, but, to a novice like me, which seem to be mismatched.
I’ll lay out here the list of resources available to me. I want to get an AM rig on the air with a decent enough signal. I wonder if you’d be able to guide me through this ‘fog’ and point me to something which will work.
1 x Talking House TH5 AM Transmitter
1 x Mosquito 1 Watt AM Transmitter.
1 x Talking House Range Extender
25ft x 75 Ohm RG6 coax cable (for Range Extender)
100Ft x CT100 50 Ohm coax (Difference between RG6 and CT100 is the loss, RG6 has solid polythene insulation, whereas CT100 is semi air spaced and larger diameter. The UHF loss is significantly less (about half as much).
1 x 20ft free standing aluminium mast
1 x 30ft tree in the garden
1 x concrete slab shed adjacent to aluminium mast. With AC power and CAT6 feed. Houses washing machine, clothes dryer, water pump and water cylinder.
Instructions for The Talking House; “Range Extender was designed for use with 75 Ohm coaxial cable. Only 75 Ohm RG6 coax cable should be used to connect your transmitter to the range extender. Using coaxial cables of other types or impedances (eg RG58) may degrade the performance of your talking house and I A.M. Radios Transmitter system”
Instructions for the Mosquito 1 Watt AM Transmitter; Use 3 metre loaded vertical antenna or alternative 50 Ohm. Best efficiency when using a 3 metre vertical antenna.
Do not operate the transmitter without either
A 50 Ohm Dummy Load or
A 50 Ohm Antenna correctly matched and tuned to the frequency selected.
The questions are:
Can I connect the TH Range Extender with the 25ft 75 Ohm RG6 coax cable to the Mosquito AM TX which states that one should only use 50 Ohm?
Can I run the CT100 50 Ohm coax up the 20ft free standing mast and then horizontally approx. 40 ft down the site to the tree, creating an inverted L antenna without a loaded coil?
How do I create a 3 metre 50 Ohm loaded coil which will work with the Mosquito?
Can you see something else I can use what is available to me?
Any solution must be carried out by a novice (i.e. me). I do not own a Soldering Iron, nor do I know how to use one. I’m a plug n play kinda guy.
Thanks guys.June 27, 2020 at 12:56 pm #115245
What I can say is use the 75 ohm cable with the talking house as if you use that with the Mosquito it’s not matching the impedence it says to use and will degrade the signal and you will get more reflected power back to the transmitter. Go by the instructions and use a 3 meter wire with the Mosquito as stated.
Some of your questions are over and above legal operation as with the Mosquito so I can’t comment more on that or the inverted L antenna which you are saying is over 40 ft. I can only say use the Talking House with the range extender.
I am not an engineer so I can’t advise you what to do for a 50 ohm loading coil. Have you checked youtube?
Sorry I can’t be of more help.June 27, 2020 at 4:14 pm #115246
Thanks Mark. Forgot to say, I’m not in the USA, so your FCC restrictions don’t apply in this case.
You mention using a 3m wire for the mosquito. What type of wire would that be? Would 50 Ohm coax cable be considered as a ‘wire’?
Re: the loaded coil. Yep, did lots of internet searches and they all seem to relate to CB or Ham Radio. I’ve yet to see any vids referring to broadcast AM….so the question still stands.June 27, 2020 at 9:09 pm #115247
No, a coax is not the same as a length of wire. A coax is shielded with ground as shield and conductor in the center so it wouldn’t radiate.
You need a length of wire like speaker wire and the thicker gauge is better. You have to split the two parts for a single wire antenna. Or any stranded wire 12 or 14 gauge in a 3 meter length.
The Mosquito says to use this as the tuning section in the transmitter is designed to work with the 3 meter antenna. Also for best results it says use *loaded* 3 meter wire which means a loading coil which will give you the effect of electrically not physically lengthening the wire. The Mosquito doesn’t have the coil in the transmitter in the tuning section so you have to make it yourself. Youtube has some videos on making coils for AM transmitters. It will work without it but not as good but with a watt you will still get some decent range.
I’m in Canada so the FCC doesn’t apply here either but with AM it’s the same.
Here’s some info on making a coil from another AM transmitter site that’s not in business anymore.
http://www.sstran.com/pages/COMMON/sstran_buildant.htmlJune 28, 2020 at 3:00 am #115249radio8zSenior Moderator
Total posts : 247
Don’t get hung up about the impedance of the coax. For practical purposes in part 15 (in the US this means license free radio) considering the power levels involved this is not a controlling factor. I operate here using 75 ohm hard line for my VHF transmitter ham system and get a reliable 40 mile range with a 25 watt transmitter designed for a 50 ohm load. I had a repeater on the air at 250 Watts with the same hard iine and it worked just fine. The loss associated with a 75 ohm coax compared with a 50 ohm coax connected to a perfect 50 + j0 ohm load is small.
The fact is that unless carefully designed matching networks are used no 3 meter antenna, base loaded or not, will present a 50 ohm load to a transmitter or feed line. I know of no one who has described such a “perfect” 50 ohm match for license free AM BCB applications. My 3 meter base coil loaded resonant antenna presents an impedance of about 30 ohms to the transmitter. My station uses a transmitter which I designed and built to drive a 30 ohm load and which is mounted at the base of the antenna system with no coax at all so the coax impedance is not a factor. My transmitter drives a 30 ohm load, by design, but most don’t, in fact, it is rare that such information is given in the transmitter specifications and folks get wrapped around the axle fixated on 50 ohm systems when such is not the case at all and 50 ohms is irrelevant. In fact, the output impedance of a typical transmitter needs to far less than 50 ohms lest a great deal of power is wasted in the final transmitter stage.
Since you have stated that you are not a technical expert then my recommendation is to use a length of wire or a factory provided ATU and quit worrying about esoteric things such as coax impedance and SWR and a lot of other tech terms bandied about and just focus on getting on the air.l Get on the air and have fun but keep in mind the limitations imposed by regulations will limit your range. You will improve your station as you gain more experience, so don’t wait until everything is perfect to have some fun.
That being said, it appears you have a defective transmitter. Pursue this.
NeilJune 28, 2020 at 1:16 pm #115251
@Mark, thank you for the explainer re: coax and wire. Seems basic to most int the hobby, but as my maths teacher used to say “there’s never a stupid question’, that’s why I asked. Can your clear answer cleared it up for me. Ill look forward to viewing that YouTube video too. Thank you for the link.
@Radio8z Thank you for the insight in relation to Ohms. I’ll have to digest this however I think the most sage thing you said was “….quit worrying about esoteric things such as coax impedance and SWR and a lot of other tech terms bandied about and just focus on getting on the air. Get on the air and have fun……. so don’t wait until everything is perfect to have some fun.” That’s the (gentle) kick up the pants I need. The best advice anyone can give, and you know, you are right, 100% right.
Guys, thank you for your patience and considered opinions. They are appreciated.
Pat.July 1, 2020 at 5:10 pm #115268
Don’t think I would take the mosquito transmitter and hook the range extender to it. the difference between 50 and 75 ohm is relatively minimal and it should work just fine. Just tune it and watch your meter for the maximum results. That 1 watt signal should give you a nice good range you should be heard from 1.5 to 2 mi with little or no difficulty at all.
I’m not sure if the connector on the mosquito is an RCA and a half or a BNC but you can buy adapters from eBay to convert those connectors to the f connector which is a female which is the same type of connector you will need for the range extender. Good luck and let’s rock.July 1, 2020 at 5:18 pm #115269
I’m sorry but the stupid thing won’t let me edit what I posted after I posted it.
just take the mosquito transmitter and connect it to the range extender. If the mosquito has a different connector other than the f connector you can get an adapter on eBay to convert RCA to f connector which is a female connector or BNC to f connector. the difference between 50 and 75 ohms is minimal and it should not make much of a difference it will not hurt your transmitter one bit. With 1 Watt expect 1.5 to 3 miles so it will cover a small town.
if you can put your results on YouTube I would love to see the range that you get on that thing.July 2, 2020 at 5:47 pm #115309DJboutitParticipant
Total posts : 67
1watt is illegal on both AM and FM just sayingJuly 2, 2020 at 6:15 pm #115310
He’s not in the USA or Canada. I believe Ireland if not mistaken.July 3, 2020 at 2:26 pm #115312
Australia from what I read also allows a Lot More Power than the USA on AM!
It is interesting to know that the USA and Canada are more restrictive but at least Canada allows more power on FM (For What Its Worth) than the USA but Canada is starting to have those pesky AM translators on FM filling it all up.July 3, 2020 at 9:06 pm #115318radio8zSenior Moderator
Total posts : 247
Can we please get back to the topic of the original post and help and encourage Pat to get on the air.
Griping about the power/field strength limits in various countries is not helping him.
Add something positive and useful.
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