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Large plate capacitor

Over the past few weeks I have been very busy with work and not really anytime for radio or anything else really. I was on the radio for a very short time last week and the weather outside was very humid and HOT! The antenna I have is the MFJ 1788 loop and I have always been able to get a decent SWR on most bands the antenna was designed for. But for some reason I was not able to get an SWR under 2.1:1 on some bands the best I could do was 3.1:1. It turns out that the Humidity can affect the MFJ 1788 antenna and my guess is since the antenna has a large moving plate capacitor the humid air affects the air gap between the plates? The other day the weather was back to cooler non humid conditions and I tried the antenna again and the great SWR was back again. The antenna had not moved and nothing had changed other than the weather.
Mike Weir, VE9KK, is a regular contributor to AmateurRadio.com and writes from New Brunswick, Canada. Contact him at ve9kk@hotmail.com.

http://www.youtube.com/watch?v=pLOJXvkBbkg

FEMA Director Craig Fugate, KK4INZ, debunks the argument that Amateur Radio is no longer relevant in our hyper-connected smartphone, tablet, satellite phone, networked radio system world:

“If you really want to short-circuit your local or state emergency manager who says that Amateur Radio isn’t really viable anymore… ask them this,” said Fugate. “Can you communicate across your jurisdiction or across your state without touching the public switched network?”

Matt Thomas, W1MST, is the managing editor of AmateurRadio.com. Contact him at editor@amateurradio.com.

Over here in G (or M or 2) land echolink nodes need to have permissions from the grown ups. So I’ve sought permission from Ofcom, with the help of the RSGB. I applied for an MB7 node, which means it is can be unattended. In order to do this I needed a minimum of 4 people who are key holders so the node can be shut down quickly. Sounds reasonable? Sounds a bit British to me. Belt and braces and some more belts just for luck.

The node will hopefully be on 2m and I have been told that if it gets granted then I could expect around 2w ERP. I don’t want to sound selfish but I have only heard 2m simplex used in this area for the local net and once in a blue moon Dent gets activated by a SOTA or WOTA chap(ess). VHF in general is scarcely used and its a shame.  UKAC evenings and the normally quiet repeaters with their occasional skeds excepting mean that both 2m and 70cms are dead.

What can be done about it?

Making it appealing to use, perhaps? A bit of activity always helps.

Internet link may give some users an opportunity not only with existing amateurs but could make it appealing to those on the periphery of the hobby. Makers for example.

Anyway, let the waiting begin and we’ll see where we get to with Ofcom

Alex Hill, G7KSE, is a regular contributor to AmateurRadio.com and writes from Cumbria, UK. Contact him at g7kse@yahoo.co.uk.

AmateurLogic.TV Episode 70 is now available for download.

George builds a remote control antenna disconnect switch with an Arduino and a Servo. Tommy experiments with the MFJ Ultrasonic Noise Locator. Peter participates in the 2014 DATV QSO Party.

Details on our 9th Anniversary Sweepstakes giveaway of the Ultimate Mobile Station.

Upcoming personal appearance, events and more…

1:20:13 of ALTV Enjoyment.

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YouTube

George Thomas, W5JDX, is co-host of AmateurLogic.TV, an original amateur radio video program hosted by George Thomas (W5JDX), Tommy Martin (N5ZNO), Peter Berrett (VK3PB), and Emile Diodene (KE5QKR). Contact him at george@amateurlogic.tv.

AmateurRadio.com is offering a free prize drawing!

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Matt Thomas, W1MST, is the managing editor of AmateurRadio.com. Contact him at editor@amateurradio.com.

As I suspected the microphone amplifier Q1 in the Kenwood/Trio TR9500 was indeed faulty. The replacement arrived next day and within an hour I had successfully soldered in the new 2SC2240 transistor and it now had audio on transmit.

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)

RECEIVER CIRCUIT
.... 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
— Andrew Garratt (@nerdsville) September 9, 2014

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, MØNRD, is a regular contributor to AmateurRadio.com and writes from East Midlands, England. Contact him at nerdsville@gmail.com.

It's been over a month since my last post. The day job, busy weekends and yes even a little radio have kept me occupied. I won't bore you with the non radio stuff, but I'll try to hit the highlights of the last few weeks.

SOTA

I've been on a couple of SOTA excursions. The first was mid-August to the Davis Mountains in West Texas. If you have never been there, it is an oasis in the middle of a desert. With mountain elevations in the 6 -7,000 ft. ASL, the climate is much closer to a summer alpine climate than a desert climate. Afternoon showers keep the entire area lush and green. I partnered with Mike,  KD5KC on this trip and did three summits, Pine Peak W5T/DW-003, Summit 6641, W5T/DW-018 and Locke Mount, W5T/DE-003. Locke Mount is the home of the McDonald Observatory.

Pine Peak was a first activation for that summit. It is located within the Nature Conservancy boundary, It is open to the public a couple of weekends a year, so we made sure to be there that weekend. It is a pure bushwhack with no trails to the top, so we had fun making a path.


Mike Crownover, AD5A, is a regular contributor to AmateurRadio.com and writes from Texas, USA. Contact him at ad5a@gvtc.com.