Posts Tagged ‘432MHz’
I have a small Moonraker 7-element ZL-Special on the main antenna mast, purchased originally for monitoring satellites and was pressed into service for SSB when I got licensed. It has never wowed me performance wise and I have been intending to replace it for quite a while but since I only use it one day a month it hasn't been a priority. So the mast came down last night and I removed it so I can take it out with me to operate portable from some higher ground tonight.
|Using the 2m delta beam in June 2014
Last year I had a go at operating portable from the car and posted a write-up. It is my intention to repeat this exercise but with the 70cm antenna on top of my 'painters pole' mast. I have serviced the antenna and fitted a new short run of quality coax and spent a far amount of time with the AW07A analyser adjusting the antenna's tuning capacitor and have got the VSWR right down to 1.1:1 on 432.200MHz so things should be optimal.
I am looking forward to this evening, hoping it pays some dividends.
As I mentioned the 24 hour March 144/432MHz VHF Championship contest took place last weekend. I took part to give away some points just grabbing a few short sessions with the radio. I concentrated on the 2m band due to my issues on 70cm.
In my AW07A analyser review I mentioned some issues with my 2m LFA YAGI, thankfully these have been resolved. The use of some wire wool to remove some corrosion and a hacksaw to take 10mm from the long elements of the loop allowed the end elements to 'trombone' in sufficiently to get the antenna resonant and the VSWR is down to 1.2:1 on 144.300Mhz.
I only made 18 contacts, but was happy with the distances achieved with 30W, getting a lot further south than I normally do, given I am 18m ASL. There was also some local wideband noise (I captured a screenshot on the SDR) and the conditions gave some interesting fading.
|M0NRD QSO map March 144 VHF
|Noise across the band
Transmitting into a dummy load and monitoring on my FT857-D the FM transmission was fine, the SSB was okay, perhaps slightly over driven. I suspected that maybe the previous owner might have twiddled something to compensate for a failing Q1.
In the adjustments section of the service manual VR6 on the IF unit controls the SSB MIC gain. To check the settings it was a case of setting the transmitter to 432MHz and putting an audio frequency signals of 1.5kHz of amplitude 1mV and 10mV from my signal generator on to the microphone terminal, and observing the RF power output, which were the 5W and just over 10W as required. As this didn't need altering I left it alone and boxed it back up and returned it to the happy owner.
Last night was the RSGB 432MHz UKAC Contest and I was hoping to here it on the air, sadly I didn't. It now transpires that there maybe another issue with it, something I should have spotted.
I do remember something strange when doing the initial testing. Connected to a dummy load and in SSB mode the S-meter showed S9+ when in receive but with no audio, turning the RF gain control the meter dropped to S0 and normal white noise static could be heard. It received a SSB transmission from the FT857-D with no issue so I thought no more of it. Being over eager and not experienced with using different rigs I had mistakenly dismissed it and should really have read the operating manual more extensively.
The anomalous S9+ meter reading and no audio occured when the RF gain control was set to the maximum which is the normal recommended setting for operating, I'd simply turned the RF gain control to the minimum mitigating the issue.
Obviously the rigs owner had put the RF gain back to maximum and was now reporting it wasn't switching back to receive. In fact it is but nothing is being heard. Checking the service manual this morning and it appears there is an issue with the AGC circuit (description and block diagram below)
.... The signal is picked up from the last stage of the IF amplifier (Q23), then detected and amplified to generate the AGC voltage. The AGC time constant is automatically set according to the mode : FAST for CW; SLOW for SSB. The AGC voltage is applied to IF amplifiers Q21, Q22 and Q23 (3SK73(GR)) and RF amplifier Q51. It is also used to drive the S meter.
It seems the rig may well find itself back on the bench, however this repair could be more problematic!
As I mentioned it was the 432MHz UKAC last night and I had a decent night of search and pounce. Conditions were very strange, lots of fading and strangely some of the usual local operators were not heard. I was very pleased to catch some lift and made a couple of decent DX contacts in Northern Ireland, The Isle of Man, Northumberland as well as Essex and Cambridge.
Who needs a preamp on 432MHz with ears as good as mine? Well actually I do desperately! #ukac pic.twitter.com/WXnMBGY0uw In a few weekends it is the National Hamfest, which is held in my home town and I hoping to pick up some bargain gear to improve my UHF set up, however from past experience that may prove difficult.
— Andrew Garratt (@nerdsville) September 9, 2014
I rewired the 7-element ZL-Special on Monday night, and adjusted it to get an excellent VSWR of nearly 1:1 and mounted to the pole.
Setting up last night I raised up the pole around 19:30 and a quick check showed the VSWR was over 1:2!
Yesterday it rained and sleeted very heavily, as suspected the culprit was where I joined two pieces of coax. I had used plugs and a coupler but had run out of self-amalgamating tape to waterproof it, so had resorted to wrapping it in insulating tape... bad idea! Removing the tape it soon became evident that everything was very damp, I quickly dried all the connectors down and gave it a quick blast with a hot air gun. All sorted, the VSWR was back to just over 1:1 (must visit Screwfix for some more tape)
I was much more relaxed for this contest, it was an enjoyable but difficult evening and made just 8 contacts, claiming 762 points. I heard quite a few calls but just couldn't make myself heard. I kept popping out the shack to turn the antenna, listening to other QSOs I was able to use the locator to determine the optimum bearing.
One observation I made was the apparent poor front to back ratio, some calls coming in loudly despite the antenna being in the opposite direction which suggests the phasing isn't quite right.
The map below shows my results.
A night off next Tuesday as it's the 23cm contest, but hoping to be better set up for the following weeks 50MHz contest, hopefully getting better results than I did last time.
View UKAC 432MHz 11-Feb-2014 in a larger map