Aerial advice please

[Linnovice]

I have a Leak Stereofetic FM tuner which I use in my workshop (read fairly large garden shed) for general listening and setting up tape decks. It's a nice unit and has been fully recalibrated and recapped. I now need a small, fairly discrete, outdoor aerial for fixing to the shed that will give me a good signal. Any suggestions?
Or, I'm thinking that my main outdoor array (5 element on house roof) is about 120' away. Could I run an additional feed from this? If so, any special cable/amplifier?
Any advice would be very welcome.

['LIVEWIRE?']

If you run two receivers from the same aerial, you will, as you no doubt know, need a splitter to prevent one radio 'stealing' signal strength from th e other. You may also get losses due to the need for 120 feet of cable between your aerial and your shed.

[Hybrid tellies]

I would try a good quality low noise distribution aerial amp, one input two output, fitted in loft space of the house then a good quality low loss coax feed for the long run to your shed. Double screened satellite coax cable should do. This will also prevent any interaction between the two receivers and you can always attenuate the shorter feed from the distribution amp to the receiver in the house if its overloading the front end. Some of these multi way distribution amps have a preset gain control which can be adjusted to give the required signal levels and some have a high output which you can use for the long 120' run down to you shed.

[Nuvistor]

120 feet of RG59 75 ohm coax will give a loss of around 3.5db at 100MHz. Dependng on the type of splitter you use, a resistive splitter loss is around 6db and one using inductors around 3db, so there are quite high losses involved. Performance depends on how strong a signal the 5 element provides.

Beware of some splitters on sale, there are no matching components in some, all centre pins connected together, good for testing quarter wave stubs but useless for splitting the signal.

You could make a temporary dipole and put the on the shed and check results, that would give you an idea what is viable.

Frank
Edit, Simons suggestion is a good idea, too early in the morning for me to think of that.

[Scimitar]

Originally Posted by 'LIVEWIRE?'

If you run two receivers from the same aerial, you will, as you no doubt know, need a splitter to prevent one radio 'stealing' signal strength from th e other. You may also get losses due to the need for 120 feet of cable between your aerial and your shed.

The splitter is to keep the impedance match. If you split 2 ways, the theoretical minimum loss is 3dB. In practice the actual loss of the best splitters is 3.5dB and that applies whether you run both ports or not, it is a divider, not a switch.

I would probably use an Allrounder on a decent mast at the shed, unless the cable run is straightforward in which case that would also give you UHF. Use decent cable though, WF100 would be my choice, RG59 is not a good choice for VHF/UHF.

[PeterRoberts]

Hi,

Have you tried one of those dipoles made out of 300-ohm ribbon either inside or tacked to the outside of the workshop? Would one of those folded dipoles bent into a halo shape (All-rounder, as Scimitar suggested) do? Do you really need the performance of the big yagi? There are various small/discrete antennas you could use, but it depends on what sort of performance you are looking for (i.e. define what you mean by 'good signal') and what the signal levels are like in your location. I live on top of a hill and have a vertical DAB dipole that also brings in plenty of FM radio signals for general listening. You could even start by making your own dipole out of a piece of twin-cord wire and see how that works. Unfortunately, without being at your location and knowing exactly what you are looking for its difficult for us to provide a best-fit solution, but you have been getting plenty of suggestions!

Cheers,

Peter

[vidjoman]

I live in a poor reception area and tried one of those ribbon aerials pinned to the inside of my workshop. It basically worked for strong stations in mono but using a 10db booster gave a strong enough signal for noise free stereo reception. Also gave me an extra output for when I need a signal for something I'm working on.

[Nuvistor]

Originally Posted by Scimitar

WF100 would be my choice, RG59 is not a good choice for VHF/UHF.

Agreed the WF100 would be a better cable, I used the RG59 as an example of loss, the WF100 is around 1.5-2dB better at 100Mhz with better screening.

Frank

[winston_1]

I would have thought a 5 element on the roof in Chelmsford is going to give you plenty of signal. A simple passive splitter is the way to go. Any amplifier will add noise so avoid if possible.

[Linnovice]

Hi chaps, great stuff! Thanks very much for all the info, certainly plenty to think about and try. Logically I suppose the easiest thing to, try is the split twin wire scenario. I presume one core goes to hot pin the other to earth? Please excuse my ignorance of the theory. My listening choice is inevitably R3 or R4. At present I've jury rigged a length of coax to the roof of the shed and that picks up the local BBC station ok and an intermittent R3 on mono. Which, I presume, indicates a reasonable signal strength?

[Nuvistor]

Originally Posted by Linnovice

At present I've jury rigged a length of coax to the roof of the shed and that picks up the local BBC station ok and an intermittent R3 on mono. Which, I presume, indicates a reasonable signal strength?

Anything connected to the end of the coax or have you split the inner/outer to make a dipole?

Frank

[paulsherwin]

Like Frank, I think you should rig up a simple dipole and try that. You may be able to run it along the inside of the roof line if the shed alignment is right, or otherwise tape the elements to a garden cane and try moving it around. You just need 2 75cm lengths of wire connected to the screen and inner of the coax, though a 75:75 balun would help a bit.

Stereofetics aren't the most sensitive tuners and a bit of external amplification would probably help. You can build a simple one transistor broadband amp in a metal box in half an hour.

[Linnovice]

I've stripped the outer casing back around 18 inches and the inner around 6 inches but the cable is still intact. ie. the braided sleeve is still woven around the inner core.
So, should I remove the outer braid and arrange differently?

[G8HQP Dave]

Originally Posted by Scimitar

If you split 2 ways, the theoretical minimum loss is 3dB.

If you mean 3dB loss from input to each output (so the power is split equally) then it is actually slightly worse than that. A passive 3-port device cannot be both lossless and matched so you either have internal losses or mismatch losses or a bit of both. Off the top of my head I don't know what the theoretical minimum attenuation will be but it will be greater than 3dB.

Going back to the original question, an alternative to a dipole is a ground plane. For broadcast reception two 'radials' may be enough.

[ms660]

You could try a resonant feed line dipole, no extra metal, just coax! And maybe a bit of plastic (4 meter band shown in the video, adjust accordingly):

https://www.youtube.com/watch?v=SolE3M74Duw

Lawrence.

[AC/HL]

I've always used the rule of thumb one third to each port and the last one for losses, but I do live in a good reception area so squeezing the last dB isn't a consideration.

[Hartley118]

My workshop happens to have a steel roof and I get good results with my Quad FM3 tuner from a cheap 'low band' taxi whip (e.g. from eBay). It's attached by its magnetic base near the middle of the 'ground plane' roof. The whip is designed for 70-86 MHz, so I cut it down pro-rata to suit the broadcast FM band.

Subjectively, the signal strength and consistency is much better than the 'split feeder' indoor dipole approach.

With a wooden roof, I guess that you could fix a metallic sheet on the roof to act as a ground plane.

Martin

[Biggles]

You can buy through hole mounting antenna bases for fitting directly through the tin, just like you would in a vehicle. They perform reasonably well and are more weather resistant than a magmount. Try your local taxi firm radio fitters for a base and whip but it's likely to cost you twenty quid. Far easier to make a dipole from two stiff bits of wire cut to about 75cms and a bit of choc bloc electrical connector in the middle. Coax connects straight onto choc bloc too. Mount the whole thing on a T piece made of thin wood. Not elegant but functional.
Alan.

[Linnovice]

Y'no what? This thread has gone completely over my head now. Oh well. Back to the Floyd and Animals ��

[paulsherwin]

Just build the dipole and try it. We will then know what your reception conditions are like and whether you need anything more sophisticated.