Amateur radio - maintaining the technical standards

[T i m]

<snip>

That's the sort of thing I was thinking about.

Yup.

All that's needed / wanted in this case. ;-)

Yeah, that sounds familiar and was mentioned elsewhere.

Ok.

Yup, they are on eBay and the like.

That's the goal, just for R4 so mostly the spoken word etc.

And that was the rub and what I was trying to avoid with 'set' tuning jobby.

Well that would be ok, as long as it didn't also autotune, if it lost signal for a second (as I think the one I had did).

I nearly got there when Googling last night but was looking more for something that was a kit than just a component list, knowing how 'funny' RF can be around component layout.

That said, I was wondering if such a radio could be made stable enough to stay 'locked' on say 93.2 MHz (R4 off CP?) or would I still need some sort of user accessible trimmer if not tuner?

If it was locked on one frequency I'm guessing it could then be optimised for that (a nice high to our 'Q'?). ;-)

Cheers, T i m

[Gareth Evans]

What part of encouraging you to take an interest and to build on what you already have don't you get?

You said further that you have been an instructor and so you should understand exactly my intention for you.

From your original challenge and also the replies to you from other contributors and your responses to them, you do seem to be taking an interest in some electronic construction, so I am warmly encouraging you in your endeavours.

[Cursitor Doom]

Should they be connected:

a) Between the microphone and the mic input?

b) Between the mains socket and the mains input?

c) Between the low pass filter and the antenna?

d) At the far end of the antenna?

e) At the antenna output socket?

f) None of the above?

[Gareth Evans]

You'd be quite lucky to have an installation where there was no ATU after the LPF because of an extraordinarily well matched antenna, but if you were so equipped then the SWR bridge could be used as an emergency indication that something was at fault on the feeder or the antenna itself, otherwise a pretty pointless installation.

Usually between the TX and the ATU; ie the TX antenna output socket and not that of the ATU.

We all know that ATU is a misnomer because it does not tune the antenna but acts as an impedance transformer. The RSGB seems to prefer the name ASchew. (which seems medically undesirable :-) )

[Cursitor Doom]

You're wasting your time; the bloke's a MORON.

[Brian Reay]

Perhaps I wasn?t clear.

It had an ?auto tune? which worked surprisingly well. When you used it the first time, you pressed a button and it scanned for the first station and stopped. If that was the one you wanted, fine. If not you pressed the button again and it scanned for the next one and so on. The pain was you needed to cycle through a ?list? and there wasn?t a display. However, as I recall, it stored the last station listened to.

When I typed the first post we were on the A1, XYL was driving. I?m now home and have looked where I thought the radios where (well one of the places). I?ll keep looking and, if I find one, see if there is a part number on the IC.

[T i m]

<snip>

<snip>

No, I think you were.

Yup.

Yup, like my Yupiteru MVT-7100 scanner or my car radio come to that.

Yup ...

Yup ... and I said as long as that was the case, it wouldn't be a dealbreaker. ;-)

Thanks.

The problem will be if it turns out it re-scans (on it's own) if it loses sufficient signal strength to stay locked on (which is what I said I think the one I had did).

I assume all that sort of thing would be built into the IC itself as from what I've seen, they just have up / down (or just up) scan buttons but not much else that might influence the start of a re-scan, if the signal was lost (other than that's inside the IC etc).

If it still relied on an external tuning capacitor then we could still be in business. ;-)

Cheers, T i m

[T i m]

At least I'm a bloke, not a coward hiding behind a killfile [1] (and another country, name and email address).

Cheers, T i m

[1] You had better get that fixed as it seems you are *still* reading everything I type.

[manuel czech]

Would you consider the description Impedance Matcher rather than Impedance Transformer please ?

[manuel czech]

I was sent on a Re cross workplace first aider course many years ago and they said avoid sticking band aids and plasters of folks in case they allergic to the adhesive.

I seem to recall the best policy was put victims in the recovery position and call for an ambulance.

Do Raynet members and the similar organisations have compulsory first aid training ?

[Brian Reay]

You are, possibly, in luck.

I?ve found one of the radios. No earphones but I don?t think from where it was it was ever used.

Drop me an Email and I?ll pop it in the post.

Email on my website g8osn.net

It is a bit bigger than a match box, takes a couple of AAA batteries and by the looks of it a 3.5mm jack.

Vol, control (rotary), scan and reset button.

The clip to clip to your coat etc is broken.

[T i m]

<snip>

That would make a change. ;-)

Ok.

Thanks very much for your kind offer (for now at least) etc but 1) I've ordered a basic FM radio kit (with manual tuning) so I'd like to see how we get on with that first (and she might prefer (at least the option of) a small speaker rather than headphones etc) and 2) are we sure that the radio you have there a) will stay on a previously found frequency after a power cycle and b) won't start scanning again, if it looses signal for a bit? If it does either we will both be wasting our time. ;-(

That sounds like what I had before (I think it was a Capital Radio freebie).

Check.

Ok.

Cheers, T i m

[Ian Jackson]

In a 'traditional' HF station (which may require an ATU), the sequence should be: TX > SWR > LPF > ATU > (FEEDER) > ANT

The purpose of the ATU is to convert to 50 ohms resistive the impedance presented by the antenna (or the 'antenna system', ie the impedance seen looking into the feeder towards the antenna). This enables a 50 ohm LPF to be presented with a good 50 ohm termination.

The reason that the LPF should go AFTER the SWR meter is because there is a slight possibility that the rectifier diodes in the meter will generate harmonics (albeit usually at a very low level). Normally these are unlikely to go very far, but in the olden days, when we had VHF television, they are believed to have been responsible for a few mystery cases of TVI (especially on Band 1). It therefore follows that the best place for the SWR meter is BEFORE the LPF - and not after it.

An obvious slight flaw in this arrangement is that the SWR meter will see inevitable imperfections in the match of the LPF. In practice, these imperfections will usually be compensated for by a slight mis- (or re-) tuning of the ATU - but this will not matter provided that the input to the ATU, as 'seen' looking through the LPF, can be sensibly adjusted so that the SWR meter (and therefore the TX) sees 50 ohms.