Best antenna solution for AM/FM/TV combo?

[Resonance1]

I am refurbishing a Motorola VK-101, which is a combination TV and AM/FM radio entertainment system. I am not certain how to provide an antenna input. The unit has only one 300 Ohm antenna input, and it is switched internally between the TV and the AM/FM radio.

I think that back in the day there must have been roof TV antennae that also provided AM and FM reception, all of which were combined into a single 300 Ohm cable. Now, of course, the video will come from a 75 Ohm DVD player (or similar). There are AM/FM antennae available for purchase, but they typically provide a 300 Ohm AM output, and a separate 75 Ohm FM output.

So it seems as if I'm going to have to combine three antenna signals, two 75 Ohm and one 300 Ohm, into the single 300 Ohm input of the Motorola.

Any suggestions?

[Electronic M]

My 1948 RCA projection set uses the same antenna scheme. About 10' of wire makes a decent radio antenna for both hands.

The FM band is smack dab in the middle of the VHF TV band between channels 6 and 7 so any TV ant that covers all of the VHF band will do FM. They probably built the AM section with an RF amp and enough sensitivity and correct antenna coupling to tune AM fine off of a TV/FM only antenna.

If it were me I'd get a good FM ant (I'm partial to folded dipoles for FM) and an antenna combiner (splitter with its inputs and outputs reversed is the same thing) and hook my video source and FM ant up.

If the TV is on its own chassis then it probably sends a 300 line to a switch on the radio (or vice versa) so if you wanted you could simply modify the set to split them into 2 antenna inputs. One for radio and a separate one for TV.

I typically use an agile modulator to transmit TV wirelessly throughout my property so for my RCA I'm just going to use a single antenna that is great for FM and good enough for TV and call it good (AM will grab a signal off any old piece of wire so I'll let it take care of it self).

[Resonance1]

Excellent advice - thanks! I was forgetting, but of course the FM band is in the middle of the VHF band. I wasn't sure if the FM antenna would also pick up AM, but I'll give that a try. As you say, that's probably what Motorola had in mind - just provide enough gain and use whatever the TV antenna picks up. I prefer not to modify anything I don't have to, so I'll try the antenna combiner approach that you mentioned.

What type of "agile modulator" do you use to transmit the TV signal wirelessly? What sort of transmitting antenna? How much power?

[DavGoodlin]

Modulators are great ways to enjoy your sets. The reasonably priced ones are Blonder-tongue BAVM Z series https://www.ebay.com/itm/30354393616...Cclp%3A2047675, but need to be on a channel that both your TV receives and one not being used in your area.
The ones in that link you may consider are the channel 3 or 9, NOT channels 28 and 36, which are not UHF but cable super band. Connect a DT box, DVD, VCR to composite A-V inputs. On the output, a single wire is enough antenna to broadcast all over the house with any TV needing only a set of rabbit ears.

I have a superband BAVM that was a cable channel but ALSO corresponds to UHF-45, which is perfect for my sets with UHF. I also b-cast 3-7-11 which are not active in this area, from my outbuilding that has the video sources, rack mounted modulators and antennas for each channel up in a loft. The reception in the house is good but requires adjusting the antenna to reduce snow just like analog days. Way more than if I was using a TV in that same outbuilding.

[zeno]

Without seeing your set or schematic I would guess.......
The AM radio uses an internal ferrite loop stick antenna. Just like
almost all AM radios. Sometimes they provide an input for a
random length wire.
FM starts just above Ch 6. On most sets you can fine tune the TV
& start getting FM.
To my knowledge olden days antennas were not designed to reject FM
so everything can come in together. Newer antennas, at least the
Jerrolds I used had break off elements to reject FM. This was done
to better get Ch6 if it were fringe.
Bottom line is use a 75 to 300 ohm adapter to hook up FM & TV.
Be sure its rated to pass up to 800 MHZ.
For AM to add an external ant is involved You would have to couple
it to the loopstick by adding a winding. Hope that all helps.

73 Zeno
LFOD !

[Resonance1]

Hi Zeno,

In this case, the incoming 300 ohm wire from the single antenna input is simply switched between the TV and the radio. Within the radio, it looks like the antenna input is used as is for both FM and AM - i.e. without adding a ferrite loop stick. I'm not totally sure that those had been invented in 1948, but at least there is none here.

I think you are right about TV antennas back in the day also picking up FM. Indeed some TV's in 1948 (not this one) had continuous tuning that included the FM band.

Thanks for the suggestions!

[zeno]

Originally Posted by Resonance1

Hi Zeno,

In this case, the incoming 300 ohm wire from the single antenna input is simply switched between the TV and the radio. Within the radio, it looks like the antenna input is used as is for both FM and AM - i.e. without adding a ferrite loop stick. I'm not totally sure that those had been invented in 1948, but at least there is none here.

I think you are right about TV antennas back in the day also picking up FM. Indeed some TV's in 1948 (not this one) had continuous tuning that included the FM band.

Thanks for the suggestions!

They may have assumed the twin lead to an outdoor antenna
would act as a long wire. The other common thing on AM radios was an
air coil antenna built on the back. On Zenith consoles they used a big
air coil in a rotatable box. They were quite directional & the art work
was absolutely pissah. We had a mint late 30's Zenith in the window
& that thing could get stations like nothing else. I fired it up every morning &
put it on a big bands stations & the customers loved it. We refused
quite a few offers up to $500.

enuf fer now. I am getting carried away with memories.

73 Zeno
LFOD !

[Resonance1]

Surprise! When I put it all together with a coax TV input, the AM and FM radios can pick up the stronger stations in the area. So, no special antennae needed for the radio.