Anntenna Question


I recently had electricians put a Radio Shack FM antenna on my roof. It's wired with RG-6U cable through a couple of patch panels down to where my receiver is located. Probably about 100' of wire in all.

It doesn't help reception -- in fact, I've gone back to the little wire dipole anenna that comes with the receiver because it sounds better. I put a little Radio Schack antenna amplifier in the mix about 10' from the antenna, and that doesn't help either.

The problem is that I don't know of any way to check whether there's actually a signal on this wire! I have access to bench-quality DVM, but that's about it. Would I require an oscilliscope to check?

I'm also not sure this is the right type of wire, or that I'm hooking it to the receiver correctly.

Any advice appreciated. Thank you!

- Eric
Something is VERY wrong with your installation. Either the antenna is not oriented in the right direction, the cable was not properly connected somewhere, etc...

The cable that you are using is fine and should pose no problems whatsoever. Out of curiosity, what type of connection are you using to connect the cable to the receiver ? Sean
Hi Sean, thanks for your reply.

Any thoughts on how to "read" a signal off the cable? I guess I could just haul the receiver around the house!

The receiver has three antenna posts on the back. The middle one is for both types of antenna.

The right post is marked "GND" and is used with the middle one for a "75-ohm" antenna.

The left one is used with the middle one for a "300-ohm balanced" antenna. That's where the dipole is hooked up now.

I believe I've tried both of these, in all combinations. It's been awhile though. Basically the shield of the coax to one terminal and the core to another.

- Eric
I agree, there is something very wrong (probably no signal). The ground is for AM. The 300 ohm is the FM; should be 2 connections. The Dipole is 300 ohm Are you sure the 75ohm is being converted to 300ohm? You need a proper adapter connected to the 75 ohm RG6U to convert it to a 2 wire 300 ohm connection.
Eric- Check your receiver manual if you have it, but I am pretty sure that the 75 ohm tap on the receiver should be connected to the coax, and probably has an F connector for that purpose. If you have one of those "transformers" that comes with a VCR, you can connect that to the end of the coax and then the twin leads of that to the 300 ohm tap on the receiver. If that works, then there is a problem in the receiver with the 75 ohm tap; if it doesn't, then you are probably getting no signal. The first place I would check if that turns out to be the case would be the patch panels (why are they there?).
Thanks for the tips guys, I will give them a try (additional are welcome of course!).

The patch panel is because I very cleverly (so it seemed at the time) wired my house with RG-6u to every room a few years back (while I was wiring for data).

- Eric
Eric- do you know if all of in-wall RG6 is intact? Could be your problem, antenna is basically a passive device. BTW, if you are able to get a halfway decent signal with the dipole, then you shouldn't need an amp on the rooftop and signal should be very good (unless you got a directional w/o a rotor).
Every time you spit a signal it loses strength. If you have the antenna going to every room in the house then the signal is pretty weak in each room. You need a preamplifer once you solve the no signal problem. For televisions a signal split to 2 sets reduces the signal 30%, for 4 sets 60%. FM is a VHF signal so should be the same. Try Stark Electronics in Massachusetts. They are on the web at:

Eric, Eric.......Eric!!! KISS principle. Purchase a Magnum Dynalab for a C note and be done with this foolishness. The antenna is omnidirectional or turn it horizontal for directional. All done within the confines of your own living room. Excellent sensitivity and selectivity. Best of luck.

The antenna from RS is probably OK, and you are just loosing signal from the conectors, also how is the RG6 connected to the antenna?, Most RS antennas (multi-element Yagis)are set up for 300 Ohm lead, you will need to install a transformer to convert the 300 Ohm to 75 ohm of the RG6. A few mor notes re the RS antenna:
Yagis are VERY directional, they have well known patterns, and unless most/all of your stations are comming from one area, you will want a rotor. Unless the Yagi was designed for FM ONLY, it will cover the VHF spectrum (TV chnls 2 ~ 13; this should not pose a problem, unless you are having multipath and sensitivity problems. The suggestion of the MD ST-2 whip antenna is a good one, as it is omni-directional.
good luck.
Had the same problem.... I returned the RS antenna because it was so selective that I could no longer receive signals that it wasn't directly pointed at... I refused to get a rotor for this thing.. The RS Salesman said it would not be directional.... so he was happy to take it back, including the marks on the mast pole from being mounted. I also ended up with a Magnum Dynalabs ST2 and life is good. I use the ST2 inside my attic mounted vertically from a roof truss (to minimize the chance of lightening strikes) -- works great and invisible from the outside.
Boy, I wish I had asked here first! I didn't know there was any other sort of antenna, honestly. The antenna was cheap, but all the parts, mounting, ground spike (8' in the ground!), skilled labor to put it up.... Yikes.

This antenna is not a Yagi, it's designed for FM, a two loops crossed. I will have to check back and see how "directional" it is said to be.

I'm not actually splitting the signal -- RG6U goes everywhere but is mostly unused currently. I will check for continuity though.

Thanks again everyone.

- Eric
Eric- the crossed loop configuration is omni-directional, I believe. And the question about splitting the signal does not relate to whether there are any other devices on-line, just whether they used signal splitters at the various patch panels (one input and several outputs, like with your cable TV). Maybe you should ask the people who did the wiring.
You do not have to have components connected or turn-on in various rooms of the house. The fact that you have all that wire going everywhere weakens the signal.
Let's take another look at the initial installation. That antenna is an omni (circular reception pattern) so as long as it's not mis-installed (somehow grounded to the mast) or defective, it should perform much better than the interior dipole. It likely has 300 ohm terminals (unless self-baluned with a coaxial type F connector) so there should be a 300 ohm to 75 ohm balun between the antenna & your coax type F connector. Make sure it's a single run of coax from antenna to tuner, with no kinks or tight bends, no splitters or anything in between. Any other coax in the house is then irrelevant. RG-6 coax is very good for this application so don't wory about that one bit. Weatherproof any external connections. On your receiver, connect the coax shield to that right "ground" terminal & the coax center-conductor to that middle "75 ohm" terminal. Ensure that none of the shield's fine wires are shorting to the center conductor (both inside & outside) that would kill the signal completely.
Using a multimeter (resistance scale) with the inside coax disconnected from the receiver you should be able to look into the cable & see that balun up top. It may appear to be 75 ohms (or perhaps considerably less impedance at DC) but there should be some continuity present.
Failing all that, your receiver's 75 ohm tap may not be working? Since you know the 300 ohm tap works with the dipole, try another balun inside & connect it to the 300 ohm inputs. Failing that you may even have a defective antenna? Try connecting it into a TV set tuned to mid-VHF channels 4, 5, 6 etc. to see if any signal at all is coming down the pipe. The FM band falls right in between there so if you have no TV signals then that probably explains the lack of any FM.
As always, Bob has analyzed the problem systematically. My gut, tells me the problem is in the multi-room coax installation; either in terms of multiple splitters (although that much coax would act as an antenna of some sort and you should get some kind of signal) or in terms of a break in the walls or at one of the panels. Either way, it seems to me that if you follow Bob's fault tree, you should be able to narrow the problem down pretty tightly.
I want to thank everyone for their responses, especially Bob for his step-by-step advice.

I went back to the cable that goes to the antenna, put an ohmeter on it (as Bob advised), and it's open. I can't "see" the Balun at the antenna. So something is not right in the antenna setup. The problem is not the cable in the house.

Now if I can figure out how the heck to get up on my sharply peaked roof!

- Eric
I just purchased a new VHF marine antenna and VHF marine radio for my boat. My question is, can I use the old VHF antenna by converting the end plug from VHF to AM/FM end plug and simply plug that into my old AM/FM radio? Put another way, is the signal from a vhf antenna usable for AM/FM? I know you can buy a signal splitter and use the output from the splitter for both types of radios. The splitter costs as much as a new antenna. My existing AM/FM antenna consists of a 3' piece of covered wire. Thanks in advance.
The guys over at Audio asylum suggest limiting the RG6 cable run to 25 feet or less for least loss. Also agree about the signal splitting being a problem. If you are lucky your antenna is above your audio room. You could even try running cable out a window and up to the antenna temporarily to see how it works.Be very careful if you get up on a steep pitched roof!!! Use rope and fastening system. If a metal roof use climbing shoes. Also get a helper. My two cents.
Just wanted to let everyone know after all these years that:

1. I did get the small FM antenna working satisfactorily, there was a bad connection that I fixed per Bob Bundus' troubleshooting tips.

2. I just last month replaced that antenna with a tripod-mounted APS-9 with a rotor, tripod-mounted to my roof.

It's great, a noticeable improvement over the previous omnidirectional FM antenna. I used to get noticeable but acceptable static on our primary listening station. Now I notice no static at all. I was crossing my fingers that the APS-9 (rather than the APS-13) would be enough, and it certainly is.

Radio shack is phasing out their antenna stuff (which is where I got tripod, mast, and other mounting gear). Antennas seem to be on the way out!

- Eric