I had a rare chance to visit the tx room in the top of Aucklands Skytower. This is where all of Aucklands FM stations broadcast from, they are all multiplexed into three different sets of antenna systems from what I found out, a least one antenna system is an 8 stack of circular's, one of the others a 4 stack vertical. They have a lot of heavy filtering up there also so they can feed a group of transmitters into the same antenna system. Most transmitters are EddyStone, the audio processing is Omnia from what I was told and are all down in the studios.

Nice, cheers for sharing.

I can't decide whether those copper pipes are for cooling or RF. They seem to be the only thing going in and out of those cavity filters where you'd expect the input and output to be, yet have a strange Jubilee clip arrangement on them and have sharp corners which are almost impossible to match to any single impedance.

I think those copper pipes are connecting all the filters together in series like a train and the combined signal passing through form the previous filter. I did notice some very thick coax going into the back of each filter seperately.

Here is a picture of another 88.6 filter, you can see the coax going in. 88.6 has multiple filters/cavities as they previously were not inside the official VHF-FM freq range allocated to commercial FM stations by the government. 88.6 used to be an LPFM freq, as the lower LPFM band used to go from 88.1 - 88.7 prior to 2010, beneath 88.0 was sensitive radio telephone stuff, police/fire etc... hence the multiple cavities 88.6 had to use. For many years Auckland had no use of the LPFM frequencies 88.5,88.6,88.7 but this changed in July 2010 when the government realigned the LPFM freqs in the lower band to 87.6-88.3 and increased the power to 1w. 88.6 has a lot to do with the Maori people hence the reason for this.

Nice pictures.

Nice images there.

On a completely different note, your website (NRG New Zealand) is down. Are you not in business any more?

The website is down, i'm still in business but only selling locally and to various trusted contacts overseas due to some people copying upgrades I had done to the PCB and selling them off as their own on ebay etc...

Some may disagree with this, however it was Albert H who originally gave me help regarding upgrades to Stevens pro3 design, pointed me in the right direction. I was the one who placed the components on the PCB using software, did some prototypes, tested them then had more PCB's made, a lot of time and effort. I started selling the kits and not long after cloned PCBs resempling the exact layout for modifications I had done started turning up on ebay under the name andrew_kits. Andrew could have at-least added his own modifications going on the info Albert has provided and not copied mine 1:1.

Christine sold me all the left over transistors (quite a lot of them) and gave her permission for me to start re-producing the NRG line of products again. I also have all the files from EasyPC which Steven used, these came from a source i'm not going to name on here.

I have since gone on to reproduce the 40w PA and now working on the higher power ones.

That Skytower install brings back some memories! When I was down there (for Tait) we had some PMR kit up there too.

nrgkits.nz wrote:The website is down, i'm still in business but only selling locally and to various trusted contacts overseas due to some people copying upgrades I had done to the PCB and selling them off as their own on ebay etc...

Some may disagree with this, however it was Albert H who originally gave me help regarding upgrades to Stevens pro3 design, pointed me in the right direction. I was the one who placed the components on the PCB using software, did some prototypes, tested them then had more PCB's made, a lot of time and effort. I started selling the kits and not long after cloned PCBs resempling the exact layout for modifications I had done started turning up on ebay under the name andrew_kits. Andrew could have at-least added his own modifications going on the info Albert has provided and not copied mine 1:1.

Christine sold me all the left over transistors (quite a lot of them) and gave her permission for me to start re-producing the NRG line of products again. I also have all the files from EasyPC which Steven used, these came from a source i'm not going to name on here.

I have since gone on to reproduce the 40w PA and now working on the higher power ones.

Probably a good idea if your designs are being copied.

Admittedly, I'm guilty of buying a Pro IV PCB off Andrew _ kits and I must say they're better quality than the originals (gold plated tracks) - if the originals are like the Pro III that is. Furthermore, I could source all legit' components over here for about £40 so it was a no brainer.

Well done on the design of the Pro IV as it brings a few improvements to the already decent venerable Pro III.

Good luck with the business.

Copper pipes are "cables", low loss and high power.


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That's what I was thinking, but they've made it really difficult for themselves by making the corners sharp.

Think co-ax made from copper pipe rather than waveguide...

thewisepranker wrote:That's what I was thinking, but they've made it really difficult for themselves by making the corners sharp.

Those corners are also joints. It would be much harder to keep same distance between inner and outer pipe if the corners were round. Inside of this copper pipes are smaller diameter copper pipes and narrow teflon holders which keep them in exact center of larger pipe.

What's the dielectric, air?

Dai Pole wrote:What's the dielectric, air?

Usually, yes.

pjeva wrote: It would be much harder to keep same distance between inner and outer pipe if the corners were round. Inside of this copper pipes are smaller diameter copper pipes and narrow teflon holders which keep them in exact center of larger pipe.

No it wouldn't. If you cut a piece of tube at any angle other than perpendicular or parallel, the end profile becomes an ellipse. Hence, you would require an elliptical centre conductor at the join of the two 45 degree tubes to keep the distance constant.

thewisepranker wrote:

pjeva wrote: It would be much harder to keep same distance between inner and outer pipe if the corners were round. Inside of this copper pipes are smaller diameter copper pipes and narrow teflon holders which keep them in exact center of larger pipe.

No it wouldn't. If you cut a piece of tube at any angle other than perpendicular or parallel, the end profile becomes an ellipse. Hence, you would require an elliptical centre conductor at the join of the two 45 degree tubes to keep the distance constant.

Right angles in transmission lines do create an impedance discontinuity, you're right, but it still works. It's the same as right angles on microstrip, not optimal but plenty of people do it.