For folk interested in weak signal VHF/UHF work, a 1.6dB improvement in S/N is significant!

73,
Steve G3TXQ

If you're not in a position to notice the difference the problem lies with you not with those who strive for the last 0.1dB improvement.

Under the right circumstances 1.6dB, in fact much less, can make the difference between confirmation and failure.

Cheers

Tony

You only have to look at the S/N performance charts for a weak-signal mode like JT65B to see what a difference 1.6dB could make; it takes you from about 18% of transmissions copied to 80% of transmissions copied:
http://physics.princeton.edu/pulsar/K1J ... me2006.pdf

Of course 1.6dB makes no noticeable difference at all if you are way below the decoding threshold, or way above it; but when you are at the threshold it makes a significant difference.

Steve G3TXQ

Hi Chris, the thread holds really good advice. May I add 3 practical points?

1. Nothing wrong with hearing better than you transmit! the other way round is very irritating!

2. Weak (audio) signals go in and out of the noise. Patience at both ends will complete a QSO as you get a bit less QSB, a bit more Aircraft reflection, a bit less local QRN. It will maybe happen quicker with a bigger beam, masthead preamp, more power etc..

3. Spectrum do a RF sensing preamp for about £50. Cheap enough to try (?), and see whether it helps and highlight whether the real problem is with local noise from TVs , street lights, or strong local signals. The amp of dxers choice is a couple of hundred quid....!

4. VHF can break your heart and wallet if you let it!

73

dave

Thanks for the advice.

I take tip one seriously now. In a past existance I was what was known as a crocodile. I had significant power but lousy ears. I soon gave that up.

I don't need another hobby to waste money on but I am starting to feel the love.

I think I'll go bigger beam first and then see whats what.

Some good advice from Dave.
I must admit one of my pet hates is to call a station, who is running 25W, to be told I'm 54 when he's S9 with me.
Fine if I was running 5W but very concerning when I'm using 100W.
The advantage of the bigger beam, as with better coax, is that both TX and RX are improved.
The big thing with the higher bands is patience and a willingness to learn and understand.
Listening, watching and relating what happens on one band that indicates what might happen on another, will produce much better long term results than just randomly calling CQ, or chatting to a local.

Hepburn is looking very good at the moment.
Early Thursday in particular.
But it can disappear just as easily.

Cheers

Tony

The small increase in dbd worked for me, after several failures on 2m over a 6 month period with ZL3TY and 5B8AD off the moon with a single (Commercial) 5WL yagi with a claimed gain of 14.7dbd
I replaced it with a stacked pair of 3WL homebrew yagi's with a combined claimed gain of 16.5dbd less phasing losses, after implementing I worked both stations with a week of getting them on the mast.
For terrestrial systems 1.6db increase I recon is difficult to differentiate but point the antenna system up to a quiet part of the sky and it's much easier to realise its potential.

Most of these mast head preamps seem far more useful overcoming the average to poor front end N.F. of shack in the box rigs which according to the figs can be 5-6db N.F. when compared to a good transverter at around 1.0db N.F.

For years I used 130ft run of hardline and no masthead preamp on 2m.
67 countries to the good without one, and with an estimated overall system N.F. of around 2.5db, it's nice to have the right balance of gain and the confidence that the system "hears well", what it won't do however is hear someone on the continent coming back at me when conditions are poor with 5 or 10w when I'm running qro.
I don't believe any mast head preamp can work that well, I sold an ssb electronics MHP145 recently those things are over £500 new.
I tried it for months and it never once made the difference between copy and no copy, again I guess that is the difference when a system has a good low N.F. figure to start with.

So with my 897 it isn't exactly a good start.

Currently I'm looking at spending money on different parts of the shack. I'll probably go with a bigger beam first and then see what I can do

Oh and Tony, my 897 OR 857 the s-meter readings on 2m SSB are WAY off what you'd expect. You can hear a signal really well but it isn't registering on the meter at all.
The same happens with my 857 on 10m, a signal can not be registering but is 100% workable.

I think the meters are just poorly set up, not just a crap receive.

S meters, on most radios are meaningless.
If switching in an internal pre-amp changes the reading it is obvious that the readings are meaningless.
Initial checks on the Perseus seem to indicate the levels shown are correct.

I was going to calibrate mine but, with so many radios, in the end, I decided that it was too much trouble s I use the guestimate method of assessing S/N.
No noise=S9, mainly noise but just readable=S1, interpolate in between.
If I can arrange things so that the 28MHz IF feed, from all transverters, is available at the Perseus, I might consider calibrating that.
Particularly for the higher bands.

In reality the signal strength is not as important as the S/N.

Cheers

Tony

Tony,

Don't go suggesting that: folk will be asking for advice on how to judge between S8 (S/N = 42dB) and S9 (S/N = 48dB)

73,
Steve G3TXQ

It's easy.
Just use your calibrated signal generator, along with a Sinad meter and do extensive listening tests whilst totally sober and alert.
Mentally picture the results and apply them to live signals, in real time.
Now which is the difficult bit?
1. Calibrated signal generator.
2. SINAD meter
Or.
3. Sober.


Cheers

Tony