My Regen Aerial

[pwdrive]

Hi again Al, first off I should mention that I do need a decent aerial & a AMU & a decent earth, it's time to do all this stuff that's the problem at the moment.

In reply to the questions:

We are approx 1.5 to 2 miles from the sea at the South coast (I can see the sea from the house)
We are approx 250 ft ASL.
How does the test regen receiver compare to my Hallicrafters SX 28 ?
Well I am not making any fantastic claims but it is working and resolving SSB very well as it stands. The SX28 has an Xtal filter so on that score no comparison, having said that a crystal filter does not generally increase the sensitivity of a receiver just its usabillity.
I always maintain this view on SWL and that is to say that if it's on the wire and above the noise then most receivers will receive it to the same degree as signals cannot be plucked from the noise of the ether as if by magic, well not with old technology at least, the only difference on that score that I can see is the different signal to noise ratios and thus noise added by any receiver concerned.
The regen by it's very nature generates it's own noise when pushed into oscillation for SSB reception, to a certain extent this can be filtered out in the audio stage with some decent L/C filtering (not got that far yet)
The SX 28 uses as does the regenerodyne a seperate local oscillator source and mixer, the mixer in both cases being a 6SA7, in the regenerodyne the 6SA7 is run with lower anode and screen potentials than are used in the SX38, that aside the mixer circuits are very similar.
I cannot run these two receivers side by side for a test as I only have one 6SA7 valve and no means of recording an output other than my ears. The SX 238 like many have two RF stages but to be honest so far as I can ascertain it's only for image ratio purposes, I have some receivers with only one RF stage and they seem just as receptive to weak signals as the two stage jobs.

My earth: I don't have a dedicated ground earth yet, I just use the mains earth, for safety reasons all my stuff on the bench is earthed to the mains, having said that most of my receivers including the regenerodyne have floating aerial primary input so I have the option to connect to a dedicated ground earth independant of the chassis/mains earth for signal purposes.
The natural earth situation here has two main points of note, first the ground is literaly rock hard, we live slap bang on top of an old metaliferous mine, and approx 6" to a foot below ground level the plot plot consists of all the "deads" these principally contain the then unwanted minerals principally iron pyrites, the depth of these deads vary from a couple of feet to many feet.
In a nutshell we have a very iron rich earth!! It is a sod to dig and/or drive anything into although driving some spikes in is not a total impossibilty...just a lot of effort.
From a reception point of view what do you make of it?
I have enough room to squeeze in an 80 meter halfwave or the equivilent length of wire.
When I copied the PY station (Brazil) the other night on the regenerodyne on 40 the band was quite noisy, yet last night when I copied the W2 from Long Island the band was really clear, sadly not a lot of DX though, out of those two copies the PY station was the stongest, the Grey Line to South America always seems to be quite good if you can catch it right.
I have a B40D perminantly on the bench (I wonder why that is then...) so maybe I will split the aerial feed and try and do some rough comparisons on reception.

Lawrence.

[Skywave]

Thank you Lawrence: very informative.

First, your understanding of the significance of what, in effect, is the importance of signal + noise to noise ratio is the same as mine.

Secondly, the value of having a s.w. receiver with two tunable R.F. stages is also the same as mine. Provided the noise generated by the first R.F. stage is substantially less than the noise generated by the mixer stage, then a second tuned R.F. stage - unless it really is exceptionally noisy - will add nothing by way of improvement to the overall S/N ratio. The real benefit of a second R.F. stage is the reduction of image reception on the higher freqs., typically above 10 ~ 12 MHz. Obviously particularly relevant with a receiver with an I.F. of about 450 kHz. {Of course, you know all this, but others reading this Post might benefit from those remarks}

Thirdly, an A.M.U. / A.T.U., the desirability of for a receiver, seems to be a subject that not everyone agrees on. All I can say is that yes, I will agree that the noise level on the HF bands below about 20 ~ 25 MHz is such that the extra apparent gain provided by such a device will only provide a very small improvement is the apparent sensitivity of any receiver. However, I can only report from my experience, based on many different locations, aerials and receivers - and that is for the simplicity of what an A.T.U. / A.M.U is & the ease of construction of one - it does provide a worthwhile benefit. One particular case is evident here. My 60 ft. horizontal 'T' aerial, if connected direct to my Eddystone 888A, gives horrendous spurious responses on Top Band, simply because the Z-matching is so bad that it completely throws out of alignment the tuning of the first R.F. stage. And I have known similar effects with other receivers over the years, too.

Fourthly: I have found that with all types on end-fed 'long-wires', below about 7 MHz (approx.), a really good earth connection is important for bringing up signal strength. And despite what you say about your 'ground' there, I suspect that that factor, with your location and height a.s.l., has a significant bearing on why your relatively small and close to the ground aerial is performing so well. If, one day, you can get up a half-wave dipole at, say 30 feet, I would not be surprised if you found that you need an attenuator between it and a receiver to remove cross-modulation taking place at the 'front end' of any receiver that you hang on it.
And finally, on that subject of earthing, all the comms. radios I use here are fed with isolated, filtered, balanced mains with no 'mains earth' connection. I run a separate low-resistance R.F. earth to each receiver. I have found that that arrangement improves the overall noise performance and is worthwhile.

And that little lot, from me, will do for now!

Al.

[pwdrive]

Thanks for the reply and comments Al, although no AMU at the moment it's on the list, I'm a naughty boy...no isolating transformer yet hence all my mains earth bonding to my gear. On the receiving side a decent long wire or whatever will be the first job, then a hammer through my wifes netbook, it just wipes out the whole spectrum when in use....

Lawrence.

[pwdrive]

Forgot to mention there is an 11 KV line that runs above the edge of our Southern boundary, not much I can do about that...they are replacing all the poles on that line, one is in the corner of our plot they are coming to replace that one on the 24th May so will be off air so to speak all day, at least I will get a pole out of it (aerial pole maybe?)

Lawrence.

[tiv48]

"then a hammer through my wifes netbook, it just wipes out the whole spectrum when in use...." tell her to try it on batterys no psu
rob t

[pwdrive]

Hello Rob, it's the smps, battery no good as the netbook is used most of every day!!

Lawrence

[Skywave]

If the SMPS is an external unit, it might be worth trying this. Fit the entire unit into a metal box. Fit chokes and capacitors to the I/P and O/P leads. Connect supply earth to the metal box.

Al.

[tiv48]

hi al i have come to the conclusion that the problems with some laptop psu is that they feed wide band interfirance back down the mains lead .most have no earth conection so im not shore how the filtering is ment to work,on bad examples i have tried ferrit rings ,x2 caps in the mains socket and enclosing the psu in an earthed tin all with no luck
on one bad exsample that that some one was trying to use as a disco juke box we solved the problem by useing a toshiba psu the laptop was a dell, this seems to be a problem thats getting more wide spread .you could i supose always build a linnier psu but it would be rather large
rob t

[pwdrive]

It's all a pain, those things should be banned, I switched on my Makita cordless drill battery charger today...same thing...there is no law aginst it apparently the manufactures only have to take reasonable precautions...it's a bl**dy disgrace.

Disgruntled.