Category Archives: Shack Stuff

Mar 21

Antenna switch project

Posted on by

In the weeks leading up to the ARRL DX Phone contest this year, Eric, WG3J and I did some extensive antenna planning at his QTH in Maryland in preparation for the upcoming contest. One of this biggest concerns was the amount of coax coming into the station. During a contest last year, we encountered a ton of RF affecting computers and audio causing an RF burn or two. Fun times.

How to resolve this? Reduce your coax run length and quantity by using antenna switches.

I reviewed a number of designs online and ended up designing my own, 2 position antenna switch which injects 12VDC onto the coax, so we didn’t require additional long lengths of control wire which could end up resonating RF.
[sthumbs=16|15|12|11|10|13|14|24|22|23|19|20|17|18|21|25,72,4,n,center,]
For the next 3 weeks part of my station would be turned into an assembly line, etching circuit boards, fabricating cases, etc.

A week before the contest, Eric and I put the switches through their paces by dumping 2.5kW at 100% duty cycle for about 10-20 seconds. This would help us assure that they would hold up to the contest pace.

I ended up building five switches, 2 rated at 10kW and 3 rated at 5kW. I’m happy to report success with the design with no smoke emissions. One thing we did find was a high SWR at 15m and above, which I believe I have a fix, that needs future testing.

Jan 13

2010: State of the shack.

Posted on by

I’m not sure if I had previously posted about my acquisition of a Yaesu FT-847 or not, but in case I didn’t…

Back in September/October 2010 timeframe, I was looking to start working satellites after making contact with the International Space Station (ISS) from the car. I would end up buying a Yaesu 5400B az/el rotor, Tracking system, M2 2m circular polarized antenna and sell my Icom 746 for a Yaesu FT-847. I was set, or so I thought.

I would go on to burn out the motor twice on the 5400B rotor, with the already $1200 investment I had in the project, I would need to add an additional $900 on a 440 circular polarized antenna, and pre-amps for both. Needless to say what’s left was the 847, 2m antenna and tracking system, which most likely would go on ebay.

Recently I started getting back into digital modes, RTTY, PSK and CW and found that the 847 was quite sloppy on the receive side when trying to get selective on the station you are trying to work. With some research, I found the 847 itself had a 2.7k receive filter which was used on both SSB and CW. Quite wide for work below 170hz wide and nearby stations would end up desensing the receive causing the intended station to merely disappear.

What to do? Add filters of course! I opted to go with a different radio instead, and I’ll tell you why.

I’ve read a number of reviews about filter options for the radio including this one, which gave me hope of increasing the receive performance of the 847, although there is a fairly major flaw with the way Yaesu designed this rig. The filter that is already in place is a 2.7k and it is on full time. If I were to replace that with a 2.1 or 1.8, that would be fine for SSB phone work. Same thing with CW, drop a 250hz INRAD in the second slot and CW performance would most likely be spectacular. But what about PSK and RTTY? Both as SSB modes. Unlike the 746, there is no menu setting that I can change that would use a CW filter for SSB digital modes.

If I were to then replace the 2.7k filter with a 250hz filter for use on RTTY or PSK, the radio would then be useless for SSB Phone, because that filter would be on full time. Not exactly flexible in that respect.

So the thought was to replace this rig with a Kenwood TS-480HX and have it serve in the shack on a temporary basis, until I acquire a Flex 3000. The 480 would then go in the mobile in place of the 706 which came into the shack on the YL’s desk during the last PA QSO party.
[flgallery id=11 /]

Jan 02

HNY and much DX in 2011!

Posted on by

First off, HNY or Happy New Year for those not sporting digital modes on HF.

Any New Year’s resolutions? At first I didn’t think I had but I guess mine would be the following:

-Actually learn code (CW) besides, CQ DE N3QO, 5NN and TU. A future post…
-Not spend as much money on the hobby as I have in last 2 years, although a Flex 3000 is in works.
-Timonium Hamfest, Timonium, MD.
-Dayton Hamvention. Enough said.
-Sussex Hamfest, I missed this one in 2010 because of work on-call.
-The 2011 antenna projects. See next post.
-..and finally, operate more, build less.

Writing the last post (year in review), I realized I did more station building than actual operation. I’m hoping we have better sunspot performance this year, but now I’m poised to hunker down and start working some DX.