HS Publications Band 2/UHF Antenna Phaser

My HS Publications antenna phasing device arrived a few days ago and I eagerly gave it a try to see what I could remove from the FM broadcast band. I will document the results, step by step below, in order to show the trial and error aspects when using such a device as the success of the ability to null an unwanted signal is based entirely on getting your antennas in just the right place, as opposed to the ability of the phasing it itself, which is a resonant 'parallel tuned rejector' circuit. In other words, using the wrong antennas, or having the antennas in the wrong place, will not allow you to create the nulls where you want them. It may be necessary to play with a few antenna types and try them in various locations in order to achieve the desired results.

In my case I have a rooftop antenna for the DX, a Korner 9.2, which picks unfortunately also receives varying degrees of electrical noise from neighbouring properties. To bring about a successful removal of this noise, I need a suitably placed second antenna, a 'noise' antenna which, ideally, only receives that noise and not the signal I want to hear. You then mix together the signals from both antennas in order to cancel the noise, leaving the wanted signal. 

The phaser consists of two controls, one to control the signal amplitude and the other to effect a 180 degree phase shift of the unwanted signal. The 'noise' antenna is fed into this and then out to a Triax signal splitter where the signal is mixed with the signal from the DX antenna. 

So, in my case, the 9.2 on the roof receives the DX signal but also receives some noise. The 'noise' antenna in the loft receives the noise and, ideally, no DX. Mix the two together and the noise, common to both antenas, is cancelled out, leaving the DX, which is only present on the 9.2. That's the theory. The practice may be different, but I must stress this will be entirely down to the correct placement of the 'noise' antenna. Be prepared for a fair bit of experimentation with the antennas, but the results will hopefully be worth it. 

So, beginning the trials: I had just hooked up the phaser and fed in a 10m length of coax which ran into the loft and had no antenna connected at this point. This is a useful test as it will only receive the strongest of local signals, in my case, Belmont. I fed this into the splitter with the 9.2 and then into my Sony XDR-F1HD. I found I was immediately able to completely remove ALL local Belmont frequencies with the greatest of ease. This did not remove weaker signals because the coax is barely capable of receiving anything and only 'saw' a very weak Belmont and nothing else. Since Belmont was common to both antennas it was possible to remove it completely. I was pointing south-east in this instance:

https://app.box.com/s/tfew0t7k5lcsqbk95igg

Next I installed a horizontal Triax FM5, placing it it in the middle of the loft one metre above the floor. Unfortunately this didn't receive much of the offending electrical noise so I didn't expect any real nulling of that noise, which was exactly as it turned out. The null was certainly there but it was minimal and there was a general nulling of everything as the FM5 was picking everything up reasonably well. It just wasn't receiving enough noise. 

I tried boosting the noise antenna with a Fringe Electronics 22dB pre-amp. This actually induced more noise, but I was still able to phase out a good deal of 'everything' I was hearing! Back to that board with the drawing on it. 

There was no an ever-increasing quantity of coax patch leads on my desk. These link the splitter to the phaser, then to the pre-amp, the psu for the pre-amp and ultimately the antenna. There is lots of coaxial spaghetti across my table and I can barely see my computer screen. Did I also mention the large number of Belling Lee / F Plug apapters and connectors? It's not good to have all these extra cables inline as, despite them being short, could still receive stray signal and potentially ruin the effects of the phasing so I have tried to keep the patch leads as short as possible, the longest being about 40cm although, typically, they are half that. I will shorten them more in due course.

The above trials were done with the 9.2 antenna pointing south-east and with the Triax FM5 noise antenna in the loft pointing anywhere between north-east and south-east, right where the noise is. Even so, the fact exists that the FM5 is not receiving enough noise and probably too much 'wanted' signal, hence the above results.

The final trial using the FM5 in the loft as the noise antenna involved me rotating it 180 degrees to so it pointed directly at Belmont. Once again, the phaser still did a fair job at nulling Belmont but this time did not affect any of my wanted continental signals to the south-east, so neighbouring Lille 88.7 and Dudelange 88.9 remained untouched. This was done without the pre-amp inline, so I repeated the nulling with the pre-amp and found the null was still present, perhaps slightly deeper, but was more 'precise' and fiddly to locate with the phaser controls.

It was also possible to rotate the FM5 and the 9.2 in order to deepen the nulls even more. With this test I was able to reduce local Belmont from three bars to a very noisy zero, leaving it open for potential DX. Lille 88.7 and Dudelange 88.9 remained unaffected. I tied the same with Belmont 93.1 and obtained the same results. 93.1 seems to be a little stronger that the other Belmont outlets, or at least it has always been the most difficult frequency to null or for the DX to breach. It is so refreshing to lift out this transmitter and leave 93.0 and 93.2 splatter free.

So far, the most successful nulling of Belmont was brought about when I only used the 10m coax feed as my noise antenna. The results with the Triax FM5 were different so I wondered if I might get better results if I used a simpler noise system. Here is a recording of Belmont being lifted out by a good 95% to leave a weak Langenberg mixing in. First you will hear the null being induced, then you will hear Langenberg struggling to compete, then I play a bit of WDR5's web stream to confirm to myself that it was genuinely Langenberg that I was receiving. Towards the end of the recording you will hear quick snippets of me tuning down to Lille on 88.7 and Dudelange on 88.9 to ensure I hadn't lifted them out too. This is another big step forward.

https://app.box.com/s/voezgqs7yk8btqloe582

Moving ahead another day ... it's now Sunday the 6th and I have been using only the driven element of the FM5 on a rotator in the loft. The phasing with this is pants. I decided to just DX with the 9.2 barefoot and immediately noticed an increase in noise. Hmm. Now then, does the simple fact of having the noise antenna connected in with the 9.2 reduce the noise? It seems it does! More experiments show that there is no 'obvious' loss of signal when the loft antenna and phaser are inline. But this actually cleans up some of the general noise and not to the detriment of the wanted signal. Very interesting indeed! Conditions are quite flat today, if not slightly less than flat, and I am hearing more continentals with these inline than without, so there is definitely a null on the general noise which is helping. The only concern is that the extra bits and pieces that are connected don't spoil the beam of the 9.2. It doesn't seem to be doing. Also, I no longer hear the rise in noise levels when I swing the 9.2 round from south to east. This is a big improvement.

As I understand it, there is supposed to be a 3dB loss when inserting the Triax signal splitter. In reality, I don't notice anything drastic, if at all, but I could always insert the Fringe pre-amp between the splitter and the XDR in order to boost any losses. It doesn't seem necessary though. This is a 'before and after' comparison with the phaser tuned in and tuned out again. I do this quite rapidly so hopefully you will hear the results easily. You can hear the noise levels lift up and out while I am tuned to a very weak BBC Radio 2 from Manningtree on 88.1.

https://app.box.com/s/dsc3zl8hyrwzck784pi1

It's not a great example as the noise antenna wasn't picking up much noise, but it was one of the first tests I did a couple of days ago and you might just appreciate how a very weak tropo signal could be buried in that little bit of noise but would otherwise get through. You can hear how the speech gets buried under that noise.

https://app.box.com/s/dsc3zl8hyrwzck784pi1

Ideally, I need that noise antenna in a better position, but with the noise now much quieter I think I would need another external 9.2 in order to hear it.

One really useful side-effect of the phaser is the ability to null the general background FM white noise. A small loss of treble can occur on the wanted signal sometimes, but this can be really useful for very weak, down-in-the-noise tropospheric DX.

So far, I am finding the phaser to be a VERY useful device for removing unwanted broadcasts as opposed to the ability to reduce the noise. It would therefore be very useful for me to leave a rotatable, directional aerial, such as a  loft-mounted FM5 so I can remove unwanted stations. A third aerial, designed to receive the noise, would still be very useful. I am seeing great potential in this device for DXers who live in areas where the FM bands are congested.

I will add more recordings below as I continue to experiment with this device. I can see there will be some very good results once the noise antenna is more suitably positioned.